:::JAAN's Science Class:::

Food poisoning/ Food intoxication

2014-01-03T08:39:00.001-08:00

Food intoxication is a health condition which caused by consuming contaminated food that contains certain toxins. It can be caused by

- Due to naturally occurring toxins in some foods. Ex: Endemic ascitis (Pyrrolizidine alkaloids)

- Due to toxins produced by certain bacteria. Ex: Botulism, Staphyloccal toxins

- Due to toxins produced by some fungi. Ex: Aflatoxin, Fusarium toxins

- Due to toxins produced by some algae like dinoflagellates, Diatoms, Cyanobacteria

- Due to food-borne chemical poisoning

However, most common food intoxication is caused by the toxins produced by certain bacteria. It involves food poisoning in which the organism grows in food and releases a toxin from the cells. The presence of organism in the food is irrelevant to disease production. It is the toxin that gives rise to the disease. Bacterial toxins that produce intoxications are exotoxins of either enterotoxin (affecting the gut) or neurotoxin (affecting the nervous system).

Type of food poisoning	Causative agent	Type of toxin	Mode of transmission	Food commonly involve
Staphylococcus food poisoning	Staphylococcus aureus	Enterotoxin	Sources from where microorganisms enter food	Meat, fish, milk, poultry, custards, cream
Botulism	Clostridium botulinum	Neurotoxin	Spores are transferred from soil into food	Damaged leaky and rusty cans or cans with broken seals
Bacillus cereus food poisoning	Bacillus cereus	Enterotoxin	Spores from soil to food such as cereals and grains	Chinese fried rice spices, reheated boiled rice, corn flour sauce
Perfringes	Clostridium perfringens	Enterotoxin	From human feces to food via hand, flies	Meat dishes, reshuffled dishes, reheated dishes, pie salads

Staphylococcus food poisoning

The causative agent Staphylococcus aureus is gram positive coccus that occurs in singles, pairs, chains, tetrads and irregular shaped clusters. It is present in all places in the environment. Only those strains that produce enterotoxin can cause food poisoning. Food is usually contaminated from infected food handler with an active lesion or carriage can contaminate food.

Pathogenesis: When the food is stored at room temperature for a considerable time period the organism may multiply in the food and produce toxins. S.aureus produces six serologically different types of enterotoxins (A, B, C, C2, D and E). Most food poisoning is caused by enterotoxin A. Isolates commonly belong to phage type III. These enterotoxins are known to be heat stable. The type B is the most heat resistant. Enterotoxins that are inactivated in low temperatures can undergo reactivation in some food. Ingestion of as little as 23 µg of enterotoxin can induce vomiting and diarrhoea. Staphylococcal enterotoxins act as super antigens, binding to MHC II molecules and stimulating T cells to divide and produce lymphokines such as IL-2 and TNF-alpha, which induces diarrhea. The toxin acts on the receptors in the gut and sensory stimulus is carried to the vomiting center in the brain.

Incubation period: Usually 1-6 hours as it’s a preformed toxin.

Clinical features: The onset is sudden and is characterized by vomiting and diarrhea but no fever. The illness lasts less than 12 hours. There are no complications and treatment is usually not necessary.

Botulism

The causative agent is a gram positive anaerobic spore bearing bacillus that is widely distributed in soil, sediments of lakes and ponds, and decaying vegetation.

Pathogenesis: There are seven toxigenic types of the organism exist, each producing an immunologically distinct form of botulinum toxin. These neurotoxins are designated A, B, C1, D, E, F, and G. The spores may germinate and produce botulinum toxin when contaminated food has been inadequately sterilized or canned improperly. The toxin is released only after the death and lysis of cells. The toxin resists digestion and is absorbed by the upper part of the GI tract and then into the blood. It then reaches the peripheral neuromuscular synapses where the toxin binds to the presynaptic stimulatory terminals and blocks the release of the neurotransmitter acetylcholine. This results in flaccid paralysis. Even 1-2 µg of toxin can be lethal to humans.

Clinical features: Vomiting, thirst, dryness of mouth, constipation, blurred-vision, difficulty in speaking, breathing and swallowing. Coma or delirium may occur in some cases. Death may occur due to respiratory paralysis within 7 days.

Bacillus cereus food poisoning

The causative agent Bacillus cereus is a gram positive aerobic spore bearing bacillus. It is found abundantly in environment and vegetation.

Pathogenesis: Sporulation is associated with toxin production. This bacterium causes two types of food-borne intoxications; the ‘emetic-type’ or the short incubation type and ‘diarrheal form’ or the long-incubation type. The short-incubation form is caused by a preformed heat-stable enterotoxin. This is most often associated with fried rice that has been cooked and then held at warm temperatures for several hours. The toxin is heat-stable, and can easily withstand the brief high temperatures used to cook fried rice. The longincubation form of illness is mediated by a heat-labile enterotoxin which activates intestinal adenylate cyclase and causes intestinal fluid secretion. This is frequently associated with meat or vegetable-containing foods after cooking.

Clinical features: The short incubation form has an incubation period of 1 to 6 hours. It is characterized by nausea, vomiting and abdominal cramps and resembles S. aureus food poisoning in its symptoms and incubation period. The second type is manifested primarily by abdominal cramps and diarrhea with an incubation period of 8 to 16 hours. Diarrhea may be a small volume or profuse and watery and it resembles food poisoning caused by Clostridium perfringens. In either type, the illness usually lasts less than 24 hours after onset.

Perfringes

The causative agent Clostridium perfringens is a gram positive anaerobic spore bearing bacilli that is present abundantly in the environment, vegetation, sewage and animal feces.

Pathogenesis: The bacterium is known to produce at least 12 different toxins. Food poisoning is mainly caused by Type A strains, which produces alpha and theta toxins. Spores in food may survive cooking and then germinate when they are improperly stored. When these vegetative cells form endospores in the intestine, they release enterotoxins. The toxins result in excessive fluid accumulation in the intestinal lumen.

Incubation period: 8-24 hours

Clinical features: Illness is characterized by acute abdominal pain, diarrhea, and vomiting. Illness is self-limiting and patient recovers in 18-24 hours.

Mushroom poisoning

2014-01-01T23:18:00.003-08:00

Ingestion of potentially poisonous mushrooms leads to the harmful health effect of mushroom poisoning which is also known as Mycetism. Previous experience and observation make it possible to discriminate between poisonous and non-poisonous mushrooms. Depending on the type of mushroom, the adverse effects range from mild gastrointestinal (GI) symptoms to major cytotoxic effects resulting in organ failure and death. Toxicity may also vary depending on the amount and age of the mushroom, the season, the geographic location and the way in which the mushroom was prepared prior to ingestion. Consumption of poisonous mushrooms can cause various types of reactions, such as allergic gastroenteritis, psychological relaxation and fatal liver intoxication. Mushroom poisoning occurs among four main groups of individuals: young children who ingest mushrooms inadvertently, wild-mushroom foragers, individuals attempting suicide or homicide and individuals looking for a hallucinatory high. Mushroom poisoning cannot be made nontoxic by cooking, freezing or any other way other than avoiding the consumption of the poisonous species.

i. Protoplasmic poisoning

Poisoning by the poisonous mushrooms can severely affect the protoplasm of cell resulting disturbances in the essential life functions of a cell. Chemical toxins such as Amatoxins, Hydrazines and Orelanine in mushrooms cause the protoplasmic poisoning.

Amatoxins

Amatoxins (cyclic octapeptides) represent 1 of the 3 major groups of cyclopeptides (in addition to phallotoxins and virotoxins); they are heat-stable, insoluble in water, and not destroyed by drying. The most significant of these are the alpha and beta subtypes of amanitin. Currently 10 types of amatoxins are recognized.

α-Amanitin Amanullin

Amanullinic acid Proamanullin

Amaninamide Amanin

β-Amanitin γ-Amanitin ε-Amanitin

Mushrooms that contain amatoxins;

- Death cap: Amanita phalloides

Native to Europe. The smell has been described as initially faint and honey-sweet, but strengthening with time. Introduced to Africa, North America and Australia by importation of hardwoods and conifers especially Oak which the mushroom is associated with.

- Destroying angel: Amanita bisporigera, A. ocreata, A. virosa

Amanita bisporigera and A. ocreata can be found in North America while A. virosa is native to Europe. Can be mistaken to button and horse mushrooms.

- Fool’s mushroom: Amanita verna

Found in Europe.

- Autumn skullcap: Galerina autumnalis

Found throughout the world but especially in America. Commonly grows on wood, and when on the ground when it has preference to mossy habbitats.

Hydrazines

False morel mushrooms contains a carcinogenic hydrazine, gyromitrin. It is unstable and is easily hydrolyzed to the toxic compound monomethylhydrazine. Consuming a large amount of gyromitrin can in worst case cause liver damage leading to death. Most of this toxin is removed when the mushroom is double boiled and rinsed, rendering it relatively safe for consumption. Main species of false morel is Gyromitra esculenta which is widely distributed in Europe in North America.

Orellalnine

A mycotoxin which is a pyridine N-oxide. An intense, burning thirst (polydipsia) and excessive urination (polyuria) are the first symptoms. This may be followed by nausea, headache, muscular pains, chills, spasms, and loss of consciousness. In severe cases, severe renal tubular necrosis and kidney failure may result in death (15%) several weeks after the poisoning. Caused by the Sorrel Webcap mushroom (Cortinarius orellanus) and some of its relatives.

ii. Neurotoxins

Poisonings by mushrooms that cause neurological problems are divided into three groups, based on the type of symptoms produced, and named for the substances responsible for these symptoms.

Muscarine Poisoning

This is due to the substance Muscarine which is particularly found in Inocybe and Clitocybe mushroom species. It is a highly toxic alkaloid related to the cholines and nonselective agonist of the muscarinic acetylcholine receptor. Within 15 to 30 minutes after ingestion of the mushroom increased salivation, perspiration, and lacrimation occur. Abdominal pain, severe nausea, diarrhea, blurred vision and breathing difficulties occur with large doses.

Ibotenic acid/Muscimol Poisoning

Ibotenic acid is a powerful neurotoxic isoxazole substance and Muscimol is a psychoactive alkaloid. Both substances cause the same effects, but muscimol is approximately 5 times more effective than ibotenic acid. Naturally occurring in Fly Agaric (Amanita muscaria) and Panthercap (Amanita pantherina) mushrooms Drowsiness and dizziness are the main symptoms of this type of poisoning.

Psilocybin Poisoning

Psilocybin is a tryptamine compound with a chemical structure containing an indole ring linked to an ethylamine substituent. It is structurally similar to the neurotransmitter serotonin. This is a naturally occurring toxin in mushrooms known as Psilocybin mushrooms. When consumed this cause a syndrome similar to alcohol intoxication.

iii. Gastro-Intestinal irritants

The gastrointestinal irritants are the least defined and most widespread of the mushroom toxins. Symptoms are mild, short-lived stomach discomfort to vomiting and diarrhea. The specific responsible toxins are generally unknown, but can be due to mushrooms of unusual sugars, amino acids, peptides, resins, and other compounds. Ex: Green Gill (Chlorophyllum molybdites), Tigertop (Tricholoma pardinum), Jack O'Lantern (Omphalotus illudens), Naked Brimcap (Paxillus involutus), Sickener (Russula emetica)

iv. Disulfiram-like poisoning

The disulfiram-like compound coprine, an amino acid produced by mushrooms of the genus Coprinus, notably C. atramenarius, the Alcohol Inky causes this type of poisoning. Coprine is converted to cyclopropanone hydrate in the human body. This compound interferes with the breakdown of alcohol. The symptoms are generally mild, consisting of flushing of the head and neck, tingling of the extremities, heart palpitations, headache and nausea. It is regarded as edible, with caution as it has no adverse side effects if alcohol is not consumed for about three days.

v. Miscellaneous poisoning

Young fruiting bodies of the sulfur shelf fungus Laetiporus sulphureus are regarded as edible but ingestion of it has caused digestive problems and allergies in some people. It is recommended not to it in raw form.

Aflatoxins

Aflatoxin belongs to a group of fungal toxins known as mycotoxins, and is widespread in agricultural products and food.

Toxin producing agent: Produced primarily by the fungi Aspergillus;

· Aspegillus flavus

· parasiticus

· nomius and A. niger

Associated food: Corn, figs, nuts, cereals, milk and milk products, peanuts, cottonseed, spices.

Characteristics and chemical mechanism of the toxin:

·
Classified into a number of subtypes. The most important ones are B1, B2, G1 and G2, distinguished by their fluorescent colour under ultraviolet light. In addition, aflatoxin M1 and M2 are hydroxylated metabolites of aflatoxin B1 and B2.

· Odourless, tasteless and colourless.

· Chemically stable in foods and resistant to degradation under normal cooking procedures.

· Accumulation is dependent upon weather conditions. Before harvest, the risk for the development of aflatoxin is greatest during major droughts as the number of Aspergillus spores in the air increases. These spores infect crops through areas of damage caused by insects, and inclement weather. Once infected, plant stress occurs; the production of aflatoxin is favoured. During post-harvest stage, production of aflatoxin can be worsened under storage conditions such as hot and humid storage atmosphere.

Natural occurrence:

· Aspergillus sp infect agricultural supplies either before harvest or at post-harvest stages under favourable conditions of temperature and humidity.

· The aflatoxigenic moulds are mainly found in soils and decaying vegetation.

· Occur in warmer parts of the world such as tropical/sub-tropical regions where temperature and moisture are high.

· Milk, eggs, and meat products can be contaminated because of the animal consumption of aflatoxin-contaminated feed.

Impact:

· Associated with both acute and chronic toxicity in animals and humans.

· Include acute liver damage, liver cirrhosis, and liver cancers. Symptoms may include fever, vomiting and jaundice.

· Chronic toxicity associated with consumption of low dose aflatoxin mainly in peanuts and grains.

· Epidemiologically implicated as a carcinogen in humans and an environmental contaminant which is widespread in nature.

· Recent medical research indicates that a regular diet including apiaceous vegetables such as carrots, parsnips and parsley, may reduce the carcinogenic effects of aflatoxin.

· Aflatoxin B1 can permeate through the skin. Dermal exposure to these aflatoxin in particular environmental conditions can lead to serious health risks.

· As aflatoxin B1 can cause immune suppression, exposure is associated with an increased viral load in HIV positive individuals.

Biology of two common phyto-pathogenic Oomycetes

2012-09-20T06:55:00.000-07:00

Phytophthora infestans

Obligate parasite.

Infect potatoes and tomatoes with late blight disease.

Life cycle

Mycelium: Non septate, coenocytic

Asexual reproduction

In the host tissue inter-cellular somatic hyphae colonizes and club shaped haustorias penetrate the tissues, feeding the parasite.

Sporangiophores are produced from the hyphae and emerge through stomata.

Sporangiophores produce lemon-shaped sporangia laterally and at the terminal end/apex of the sporangiphore. A Sporangium possesses a papilla on its tip.

Outcome of the sporangium depends on the temperature and humidity.

Low humidity or high temperature: Sporangium germinates by a germ tube that later results the somatic hapha.

High humidity (when raining) or low temperature (12⁰C or below: Cytoplasm of the sporangium divides and gives rise to biflagellate Zoospores. Either by dissolution of papilla or through its opening tip, zoospores are released to outside. Zoospores directly penetrate host tissue and undergo encystment in cells. They develop into germ tubes that later result the hyphae.

Sexual reproduction

Plasmogamy occurs as oogonium punches the antheridium, going through that antheridium, oogonium grows above it. The antheridium therefore appears as a funnel at the base around the oogonium. Karyogamy and meiosis occurs respectively. Oospore is spherical and adapted to adverse environmental conditions. It results out a sporangiophore that again develops into a sporangium.

via www.apsnet.org

Plasmopara viticola

Obligate parasite.

Infect grape vines with Downy mildews.

Life Cycle

Mycelium is non septate and coenocytic.

Life cycle is much similar to Phytophthora infestans as both are oomycites.

Asexual reproduction

Somatic hyphae develops in inter cellular space host tissue penetrating with haustoria.

Hyphae give rise to sporangiophores that emerge through stomata, branching and producing sporangia at each apex of the branches.

Sporangia may either germinate directly into mycelium or produce kidney shaped, biflagellate zoospores, depending on humidity and temperature just like the Phytophthora infestans. Zoospores encyst in cells, germinate and result the somatic hyphae.

Sexual reproduction

Sexual phase is taken place at unfavorable conditions. Plasmogamy occurs by gametangial copulation as oogonium and anthredium come close together. Karyogamy results zygote that later gives the spherical oospore. Oospore divides by meiosis and undergoes germination producing a sporangium.

More about downy mildew http://fruit.cfans.umn.edu/grape/IPM/downy.pdf

Insect Abdomen: Appendages found on the abdomen

2012-07-13T02:09:00.001-07:00

Insect abdomen is the third functional region of insect body. It is located behind the thorax and contains 6-10 segments. There are various types of appendages arise from the abdomen.

Cerci

Located close to anus.

-Blattodea: simple and jointed cerci

Via ediacaran.mech.northwestern.edu

-Orthoptera: simple and not jointed cerci

-Dermaptera: Sclerotized, forceps like cerci

Dermaptera forcep like cerci via gallurapestcontrol.com

-Thysanura: Long filamentous cerci

Long filamentous cerci of Thysanura

-Ephemeroptera larvae: Wing like cerci that helps to move forward in water.

Wing like cerci -Ephemeroptera larva

Styles

Can be seen in Cockroach and Lepisma. It is regarded as the vestige of the walking limb.

via microscopy-uk.org.uk

Median caudal filament

This is a thread like projection arising from he center of the last abdominal segment between the cerci.

Abdominal Prolegs

Can be seen in Lepidopera.

via entomology.umn.edu

Abdominal Gills

These are respiratory organs and found in nymphs of some aquatic insects.

Cornicles

These are located dorsally on the abdomen as paired secretory structures.

Female External Genitalia

Ovipositors are used for oviposition and it is formed by the modification of 8-9 abdominal segments. Thysanura, Orthoptera, Thysanoptera and some Hymenoptera insects contain true ovipositors.

Ovipositor places egg inside caterpillar

Egg is released (naturecloseups.com)

-The ovipositor is modified as a poison injecting sting ( Wasps, bees..etc)

via amazingnature.us

-Hind end of the abdomen is extended to work as an ovipositor

Male genitalia

Modification of 9^th abdominal segment makes the copulatory organ of males which is consist of aedeagus and pair of lateral claspers to grasp and hold the abdomen of the female during mating.

Special reactions/tests for Urea, Formamide, Oxamide, Salicylamide, Succinimide, Phthalimide

2012-07-09T08:31:00.001-07:00

Urea

Urea nitrate and oxalate: Take a concentrated solution of urea, to one portion, add a few drops of con. HNO₃: the white crystalline urea nitrate (m.p. is 163°) is precipitated; to another portion, add con. Oxalic acid solution and scratch with a glass rod. White crystals of urea oxalate (m.p. is 171°) are separated. In an excess of water both salts dissolve.

Biurate reaction: Take 0-2 g of urea into a dry test-tube and heat gently above the melting point. NH₃ is evolved. After 2 minutes the liquid rapidly solidifies with the formation of biuret.

2NH₂CONH₂à NH₂CONHCONH₂ + NH₃

Dissolve the solid residue in a few ml. of warm 10% NaOH solution. Stand it to cool and add 1 drop of dil. CuSO₄ solution. A purple coloration is obtained. A pink/purple coloration is due to containing two -CONH- groups attached to one another, or to the same carbon atom or nitrogen atom. Therefore the same colouration is also given by malonamide, oxamide and by proteins/peptides.

Urease test: Urease enzymes can hydrolys Urea to Ammonium carbonate. The reaction is specific. It is used for solutions of urea to which the biuret test cannot be applied.

Action of hypobromite: Add sodium hypobromite solution to a solution of urea. The brisk effervescence is given.

NH₂CONH₂ + 3NaOBr à N₂ + CO2 + 3NaBr + 2H₂O

Formamide

Boil 1 ml of formamide in a test-tube. NH₃is evolved from it. CO is produced, but cannot be ignited in the presence of the NH₃.

Oxamide

Biuret test: Oxamide does not need any preliminary treatment to proceed with the test. Shake 1 g of oxamide with 1ml of 10% NaOH solution. Add 1 drop of very dilute CuSO₄ solution to it and mix well. A pink coloration is produced.

Sulphuric acid test: Heat 0-3 g of Oxamide with con. H₂SO₄. CO and CO₂ are evolved.

Salicylamide

FeCl₃coloration: Take the solid into a test tube. Add FeCl₃ solution and shake. An intense violet coloration is produced as the Phenolic groups are present.

Succinimide

Reduction: Take about 1 g of succinimide and an equal amount of Zn dust into a dry hard-glass test tube and mix well. Heat strongly. Soak a pinewood splinter in con.HCl and place it in the mouth of the tube. The splinter is turned red by the vapour of pyrrole which is formed by reduction.

Fluorescein reaction: Take about 1 g of Succinimide, 1 g of resorcinol and 2 drops of con. H₂SO₄into a dry test tube and fuse all of it together. Cool and add water. Then add NaOH solution in excess. A green fluorescent solution is produced.

Phthalimide

Phthalein reaction: Take about 1 g of Phthalimide, 1 g of phenol and 2 drops of con. H₂SO₄into a dry test-tube and fuse all together very gently. Let it cool and add water. Then add NaOH solution in excess. A red coloration is produced which is decolorized by acids.

Fluorescein reaction: Repeat the above test, using resorcinol instead of phenol. A green fluorescent solution is produced on the addition of NaOH solution.

Physical properties of common organic compounds (In brief)

2012-07-07T08:49:00.001-07:00

One of the easiest ways to get an idea about an unknown organic substance is to check for its physical properties first. Physical properties are appearance, state, odour, colour, solubility in water etc. Below are some general physical properties of common organic substances.

Odour

Fruity odour: Esters, ethers.

Odour of almonds: Benzaldehyde, Nitrobenzene, Benzonitrile,

Pungent odour: Pyridine, Formic acid, Acetic acid, Benzoyl chloride, Benzyl chloride, Acetyl chloride.

Many phenols give a unique Phenolic odour. Also some derivatives of salicylic acid such as Salicylaldehyde.

Colour

Orange: Ortho-Nitro-aniline, Alizarin.

Yellow: Quinones, m-nitroaniline, o-nitrophenol, and many other nitro-compounds. Also Iodoform.

Red: i,2-Naphthoquinone.

Blue: Commonly Copper salts.

Solubility in water

Soluble in cold water: Lower aliphatic alcohols, lower aliphatic aldehydes & ketones, lower aliphatic nitriles, lower aliphatic acid chlorides, aliphatic amines, pyridine, salts of amines, glycine, some phenols, aliphatic acids, sulphonic acids, ammonium salts and alkali salts of all acids, methyl esters of certain acids such as formic, oxalic, succinic and tartaric. Also some aliphatic amides and imides, such as succinimide.

Almost insoluble in cold water: Higher ketones, most esters, ethers, higher alcohols, higher phenols, Benzyl alcohol, metaformaldehyde, Aromatic aldehydes, aromatic acids, aromatic amides, aromatic imides, aromatic amines, aromatic nitriles, aromatic acid anhydrides, aromatic acid chlorides, sulphonamides, sulphonyl chlorides, starch, anilides, uric acid, hydrocarbons.

Hydrolysed with water: Acids, esters can hydrolyse easily. Acid anhydrides, acid chlorides, salts of amines and nitrophenols.

Using litmus-paper on a solution

Weakly acidic: Phenols. Except for nitrated phenols, phenols do not liberate CO₂ from Na₂CO₃ solution.

Weakly alkaline: Alkali salts of some weak acids and pyridine.

Polymerase Chain Reaction ( PCR )

2012-06-25T01:00:00.000-07:00

This is a method to produce very large numbers of copies of specific DNA sequences without cloning. Therefore PCR can amplify specific sequences or add sequences such as endonuclease recognition sequences as primers to cloned DNA.

PCR consists of 5 main components.

-Target DNA

-Single stranded Oligonucleotides (primers)

-d NTPs (dATP, dCTP, dTTP, dGTP)

-Taq DNA polymerase

-Termocycler

There are three main steps in PCR.

Step1: Denaturation. The mixture of excess primer and DNA fragment is heated to about 95° C causing the double strands of target DNA to be denatured into single strands.

Step 2: Annealing of Primers. The temperature is dropped down between about 35⁰- 65°C

As the temperature decreases the single strands of DNA reassociate into double strands. Large excess of primer allows two primers anneal or bind to their complementary sequences on the target DNA leaving the rest of the fragment single-stranded.

Step 3: Primer Extension. The temperature is raised to 70⁰- 75°C Taq polymerase is added. Taq polymerase extends the primer into a complementary copy of the entire single-stranded fragment, in the 5’-3’ direction. As both the DNA strands are replicated, two copies of the original fragment are gained.

This process is repeated many times. At each time, the number of DNA copies doubles. This is continued until enough copies are gained for the analysis.

Differences between physisorption and chemisorption

2012-06-24T00:58:00.001-07:00

Different kinds of bacteriophages (phages)

2012-06-23T10:00:00.000-07:00

M13

Filamentous.

About 870nm in length and 6nm in width.

Consists of single stranded DND (ssDNA).

Three kinds of capsomeres build the capside.

Infects E. coli by adsorbing to the cell and entering through F pilli. Therefore only infect F⁺ and HFr cells. Also male specific.

Does not kill the host. Particles are released by budding, therefore when the particles are released, the host cell is alive.

An efficient vector in gene cloning as it can hold longer pieces of foreign DNA.

T phage

Structure is composed of icosahedral head, double stranded DNA and a tail.

Infects E.coli

Main types of T phages are T2, T4 and T12.

In the infection linear DNA of the phage is released to the host cell and becomes circular by replicating that later produces a long DNA chain known as ‘Concatamen’. This coils into the phage’s head by headfull mechanism while packaging.

Infection kills the host cell as the new particles are released outside by bursting the host cell.

Lambda (λ)

Composed of head and tail.

Head is consisting of double stranded linear DNA.

At both 5’ ends of the DNA strand, 12 complementary base pair, single stranded segments are present. These two ends are known as “cos ends”.

Because of the cos ends, phage chromosome circularizes before replication. Concatamen is produced during the replication and during the packaging, Terminase enzyme cuts off the cos ends.

Host cell is E.coli.

MS2

Contains the smallest known genome.

Super coiled single stranded DNA.

Infect only through sex pilli. Therefore male specific.

Infect E.coli.

Phi×174(ΦX174)

Contains a single stranded circular DNA.

After adsorption, synthesizes the complementary strand and becomes double stranded.

Use as a positive control in DNA sequencing.

Structurally similar to ΦX174 phage.

Can infect susceptible E.coli cells.

Serotonin the neurotransmitter

2012-05-06T01:02:00.001-07:00

Serotonin i.e. 5-hydroxytryptamine (5-HT) is a monoamine neurotransmitter that is said to be helping to relay signals from one area of the brain to another. However its primary functions are found in gastrointestinal tract as 90% of total serotonin is located in the enterochromaffin cells in the gut.

Serotonin is made via a unique biochemical conversion process that begins with Tryptophan. Tryptophan is a building block to proteins. In the synthesis of serotonin, Tryptophan hydroxylase the enzyme combines with tryptophan to form 5-hydroxytryptophan metabolite that later converts to Serotonin.

Via wikipedia.org

As mentioned earlier serotonin helps to distribute messages across the brain. Brain cells related to mood, appetite, sleep, memory, learning, temperature regulation, sexual desire and some social behaviour are influenced either directly or indirectly by serotonin due to the widespread distribution in the brain.

It can also affect the functioning of the cardiovascular system, muscles, and various elements in the endocrine system.

When it comes to mental health, it is widely believed that a serotonin deficiency plays a role in depression but there is no way to measure its levels in the living brain. Therefore, there have not been any studies proving that brain levels of this or any neurotransmitter are in short supply when depression or any mental illness develops. People who suffer from depression shows lower serotonin levels in blood levels but still it is not revealed that whether the blood levels reflect the brain's level of serotonin.

Antidepressant medications such as SSRIs (selective serotonin reuptake inhibitors) and SNRIs (serotonin and norepinephrine reuptake inhibitors) that work on serotonin levels are believed to lower the symptoms of depression, but their exact function is not fully understood.

Recent studies show that when the Mycobacterium vaccae, which occurs naturally in soil and is often breathed in when spending much time nature, is injected into mice, it stimulates neuron growth and causes serotonin levels in blood to increase. So that the bacteria could have antidepressant benefits but it is not yet revealed whether it has an effect on human.

Simple facts about Betalain

2012-05-02T07:56:00.000-07:00

Betalains are alkaloid pigments which are found in some families of plants belonging to the order Caryophyllales, but in no other plants.

They are named after the Beet family of plants (Beta).

Betalains are not found in plants containing anthocyanin pigments. Structurally they are unrelated. Unlike anthocyanins, they are not pH indicators as their colour is stable over a wide range of pH. They are oxidised over time going brown in colour. This can be prevented by 0.1% ascorbic acid.

They have also been found in some fungi too e.g. Fly Agaric (mushroom)

Betalains can be divided into two types as betacyanins and betaxanthins; based upon their molecular structure.

Betacyanins

Usually appear red to red violet in colour (absorbance in 535-550nm)

Betaxanthins

Usually appear yellow in colour (absorbance in 475-480nm)

Betalains are found in the vacuole and they are water-soluble.

Also they cause colour in both flowers, fruits and sometimes vegetative organs



Beetroot contains 2 Betacyanins. Thay are Betanin and a derivative.

Not much is known about the role of betalains. Commercially they are sometimes used as food colourants. As a food dye it’s cheap and no all allergic side effects are figured out yet.

Basic structure of betalain

Use of colorimeter for the determination of the concentration of a solution

2012-04-27T07:32:00.000-07:00

Absorbance is important in determining concentration of a substance in a sample through colorimeter analysis. Colorimeter measures the intensity of colour and light transmittance by the sample to achieve the concentration. When a beam of light passes through a coloured solution, the amount of light absorbed depends on the nature of the molecules absorbing the light, their concentration and thickness (path length) of the solution. The ratio of transmitted intensity to original intensity s known as the “transmittance”, T.

Transmittance (T) = I/I₀

I = intensity of the transmitted light

I₀= intensity of incident light

The Beer- Lambert law states that there is a logarithmic dependence between the transmittance and the absorbance. Therefore the transmittance is expressed in terms of absorbance;

Absorbance (A) = -log₁₀ T

= -log₁₀ (I/I₀)

According to this, the absorbance becomes linear with concentration considering;

A = ℰ ℓ C

ℰ = Molar absorbance coefficient

ℓ = path length

C = concentration of the solution

Therefore in dilute solution,

A = -log₁₀ (I/I₀) = ℰ ℓ C

Molar absorbance coefficient indicates the absorbance under a standard set of conditions, i.e. the light travelling 1cm through a solution of 1moldm^-3. In a material with a low absorption coefficient, light is poorly absorbed and vise versa. This depends on the material and on the wave length of the light.

When using the colorimeter the path length i.e. the width of the glass cell is constant. Also the concentration of one solution used at one specific wave length. Therefore ℰ is also constant through the measurements. This shows out clear relationship between the absorbance and the concentration.

A ∝ C as ℓ and ℰ are constant

The glass cell/ container with plane parallel faces are transverse by monochromatic radiation in the colorimeter. If the glass cell is filled with non absorbing solution, there is 100% transmittance; therefore the absorption would be zero.

Colorimeter applies only in relation to the visible region. Also Beer- Lambert law is applicable for 0.800-0.200 absorbances.

In the experiment, firstly the absorbance reading of the colorimeter should be zeroed using distilled water as distilled water is used to prepare the solutions.

Also before taking the measurements of the absorbance value in each solution, the glass cell should be washed with distilled water in order to prevent interferences to the reading. It is important not to touch the two smooth surfaces of the glass cell and wipe out the additional drops remain on the surfaces of the glass cell, using a tissue. Otherwise the beam of the radiation would be scattered incorrectly and interfere the accuracy of the reading.

When filling the cell, air bubbles should not be remained inside the cell as it would decrease the absorbance value.

When refilling a glass cell with a different solution, small amount of the new solution should be used to rinse the cell before filing as it would give more accurate results.

Spectrophotometer also uses a monochromatic light to pass though a solution and measure its absorbance. The principle of spectrophotometer and colorimeter is same but a colorimeter can only use one wavelength at a time and have a fixed number of wavelengths that can be used. Also they have to be in visible range only.

A spectrophotometer on the other hand can not function like a colorimeter but take a spectrum of a solution across the entire wave spectrum especially in UV – IR. Therefore use of spectrophotometer is beneficial than a colorimeter and useful to determine concentration of unknown solutions.

Applications of conductivity measurements: Calculating the solubility product of a partially soluble salt (Lab report)

2012-03-28T08:50:00.000-07:00

Theory

The solubility of poorly soluble salts is expressed as the solubility product. That is the product of the concentration of ions in the solution which are in equilibrium with the solid ion. These concentrations can be determined via conductivity measurements. In this practical PbSO₄ is used.

PbSO₄⇌ Pb²⁺ + SO₄^2-

Assume concentration of solid is a constant.

Concentration of Pb²⁺= concentration of SO₄^2- = C

\ Ksp = [Pb²⁺_aq] [SO₄^2-_aq]

Ksp = C²

The measurement of the specific conductivity, K of the saturated solution leads to a value of the concentration.

i.e. C = K/ Λ₀

As, Ksp = C²

Ksp = (K/ Λ₀)²

Λ₀for PbSO₄ = 3.02 × 10^-2 m²Smol^-

Λ₀= Molar conductivity at infinite dilution

Procedure

About 2g of finely powdered PbSO₄was measured using the electric balance into a clean, dry watch glass.

It was added to a clean beaker. The watch glass was washed with distilled water and that washed water was also added to the beaker.

To remove impurities it was shaken by adding distilled water. It was kept aside for a while, for the salt to be collected at the bottom of the beaker. Then the upper layer was decanted and repeated this step for several times.

An empty reagent bottle was kept in a water bath at 24⁰C in order to maintain the temperature of the reagent bottle at 25⁰C.

Then the well- washed salt was added to the reagent bottle and added 100mL of distilled water.

After awhile without disturbing the solid, the clear upper solution was decanted into a clean beaker and the conductivity was measured.

Results

K of distilled water at 25⁰C = 4.2 µS/cm

K of PbSO₄ at 25⁰C = 39.2 µS/cm

Calculations

Corrected conductivity of PbSO₄ = (39.2 – 4.2) µS/cm

= 35.0 µS/cm

= 35.0 × 10^-2 Sm^-

C = K/ Λ₀

C = 35.0 × 10^-2 Sm^- / 3.02 × 10^-2 m²Smol^-

C = 0.11589 molm^-3

C = 0.11589 × 10^-3moldm^-3

PbSO₄⇌ Pb²⁺ + SO₄^2-

Ksp = [Pb²⁺_aq] [SO₄^2-_aq]

Ksp = C²

Ksp = (0.11589 × 10^-3moldm^-3)²

= 1.3430 × 10^-8mol² dm^-6

Conclusion

Exact given Ksp at 25⁰C is 1.6 × 10^-8mol² dm^-6. Practically obtained Ksp at 25⁰C is 1.3430× 10^-8mol² dm^-6

As the both values are closer we can use conductivity measurements in order to calculated KSP.

Discussion

The precipitate was washed in order to remove impurities that may affect the results. It should be washed several times to obtain a well- washed precipitate. During this process, precipitate can be also removed. Therefore all 2g of the sample wouldn’t be left.

When maintaining the temperature of 25⁰C, the water bath was kept at a temperature about 24⁰C. this is because we measure the temperature of the water bath assuming the temperature inside the reagent bottle is at 25⁰C. But actually the temperature of the solution inside would be slightly higher than the temperature of the water bath as the glass of the reagent bottle separates both. Therefore the temperature of the water bath was kept at lower temperature to obtain the required temperature for the solution.

Reagent bottle should be shaken time to time when it was kept in the water bath. This is to increase the dissociation and reach the equilibrium. If not, we might have not measured the conductivity at the equilibrium and that will alter the true Ksp value.

The calculated Ksp value is slightly smaller than the exact given Ksp value due to errors occurred during the experiment. Mainly the personal errors. Such as temperature maintaining errors, measuring errors and personal carelessness.

When preparing the solutions, the distilled water was added. Distilled water also contains ions it self. Therefore additional conductivity from the distilled water would be raised in the solution. For this reason the conductivity of the solution is corrected by deducting the conductivity of water.

Physiology of Synapse:- Excitatory synapses and Inhibitory synapses

2012-03-21T08:54:00.000-07:00

Synapse is simply a junction between two neurons. There are two types of synapses in central nervous system.

· Excitatory synapses

· Inhibitory synapses

Excitatory synapses

Pre synaptic knob secretes as excitatory substance. (Ex: Acetyl choline, Noradrinalin, Gutamic acid)

Transmission:

Nerve impulse à pre synaptic knob releases acetyl choline (Ach)àAch diffuse across synaptic cleftàAch combine with receptor sites of post synaptic membraneàpermeability of post synaptic membrane changesà permeability to Na⁺ increases and Na⁺ enter the post synaptic knobà Excitatory post synaptic potential (EPSP) is obtainedàthreshold potential is reachedà action potential is formedà distribution of action potential

A combined EPSP depolarize the membrane to a threshold value to generate an action potential is known as summation. Summation can occur in two ways as temporal summation which is obtained by repeat discharge of single pre synaptic knob and spatial summation which is obtained by numerous pre synaptic knobs.

Inhibitory synapses

Pre synaptic knob secretes an inhibitory substance. (Ex: alpha butric acid and glycine)

This inhibitory synapses function in two ways as post synaptic inhibition and pre synaptic inhibition.

Post synaptic inhibition

Nerve impulseà pre synaptic knob release an inhibitory substance (GABA)àGABA diffuse across synaptic cleftà GABA binds with receptor sites on post synaptic membraneà permeability of post synaptic membrane changesà permeability to K⁺ and Cl^- ions increaseà K⁺ leaves and Cl^- ions enteràInhibitory post synaptic potential (IPSP) is obtainedà membrane hyperpolarizedà no action potential initiated

Pre synaptic inhibition

Nerve impulseà pre synaptic knob release inhibitory substancesàhyperpolarize the pre synaptic excitatory membraneà prevent excitatory substances releasingà no excitation occurs on post synaptic membrane

Sequence of events take place during action potential in brief

2012-03-21T07:45:00.000-07:00

>In resting state, membrane is permeable to K⁺ and relatively impermeable to Na⁺.

>When a stimulus depolarize the membrane into the threshold value the voltage gated Na⁺ channels open, vastly increasing the membrane’s permeability to Na⁺.

>Na⁺ enters the cell across the membrane under the influence of both concentration gradient and the electric gradient.

>Na⁺ makes the membrane more depolarized and that makes more voltage gated sodium channels to open.

>As the membrane potential approaches equilibrium potential of Na⁺ the driving force of Na⁺ is reduced. Therefore less number of Na⁺ reach into the cell.

>After a short time the voltage gated Na⁺ channels are inactivated and stop the taken in of the Na⁺. Here the membrane potential rise to +45mV.

>As this occurs, the voltage gated K⁺ channels open and greatly increases the permeability to K⁺ ions. Therefore K⁺ leaves the cell under the influence of concentration gradient and electric gradient.

>As K⁺ leaves, the positive charge inside the cell is reduced. After awhile the equilibrium potential of K⁺ is obtained and the membrane is hyperpolarized. Now the membrane potential is -75mV. Hyperpolarization is due to the delay of closing the K⁺ channels compared to Na⁺ channels.

>The voltage gated K⁺ channels close and by then the Na⁺ channels recovered by inactivation.

Basics of electroplating

2012-03-12T07:17:00.001-07:00

Electroplating is the process of depositing a layer of metal electrolytically on to a surface.The articles to be plated make the cathode of an electrolytic cell and a rod of the plating metal makes the anode.

Normally pure metals are used. E.g. Cu, Ni, Cr, Au, Ag, Pt, Zn

But there are exceptions such as Alloys (Cu-Zn, Ni-Cr) and metal with polymers or ceramics (metal-PTEF, metal- Ceramic)

Requirements for electroplating

-Proper bonding between the plating material and the surface.

-Evenness of the plating.

-Cleanliness

-Leak holes must not be left.

-Texture: should have high brightness.

-Resistant to chemicals in the environment that can cause damage.

Essential parts of electroplating

Difference between Mⁿ⁺ and complex ions

Complex ions release metal ions slowly. Therefore its concentration is low. It’s important to obtain a smooth ending.

Additional electrolyte can be used to increase the conductivity of the system but it will not effect the solution’s ions. Sodium sulphate is an additional electrolyte.

Additives

Additives increase the quality of the electroplating.

-Brighteners: Saccaric acid, Thiourea

-Levelers: Formaldehydes

-stress relievers: organic substances

-wetting agents: Sodium lauryl suphate

Factors affecting the quality of the electroplating

-Nature of the electrolyte

-Concentration of the electrolyte

-Purity of the electrolyte

-Nature of the additives

-Concentration of the additives (should be low)

-pH of the solution

-Temperature

-Current density

-Geometry of the electrode(whether it’s round or flat)

-Shape of the bath

-Flow conditions (stirring is good)

Hull cell
To study the quality of electroplating dependence on the current density.

Haring-Blum cell

To determine the throwing power of the electroplating process.

Biosynthesis and function of aromatic amino acids in plants

2012-03-12T01:26:00.000-07:00

Most aromatic amino acids in plants are formed by three main types of aromatic acids;

Phenylalanine
Tyrosine
Tryptophan

These three important aromatic amino acids are exclusively synthesized by Shikimic acid pathway that is unique to plants and microbes. This pathway got its name by an important intermediate forms,called Shikimic acid.

Shikimic acid pathway starts from the condensation of Erythrose-4-phosphate with Phosphoenolpyruvate (PEP). PEP is provided by the glycolysis while Erythrose-4-P comes from either oxidative pentose phosphate pathway or Calvin cycle. Therefore Shikimic acid pathway is combined with other important metabolic pathways of the cell.

The condensation produces 3-deoxy-D-arabinoheptulosonic acid-7-phosphate (DAHP). DAHP undergoes another series of reactions including condensation with another molecule of PEP to give out Chorismic acid. Shikimic acid forms as an intermediate in this reaction and regarded as the key intermediate.

Chorismate is a central intermediate giving rise to two products; Prephenate and Anthranillic acid. Shikimic acid pathway is shown simply as below.

The synthesis of aromatic amino acids is important as these amino acids are the precursors for the synthesis of defense and repair compounds.

Phenylalanine

· Flavonoids: in plant pigments (eg: Anthocyanine), act against pathogens. Antioxidants.

· Coumarins: Has appetite-suppressing properties.

· Liginin: In lignicolous fungi

Tyrosine

· Tocopherol: Antioxidant in cornifers.

· Plastoquinone: Important in photosynthesis.

· Cyanogenic glucosides: Phytoanticipants. Important in plant defense against herbivores due to bitter taste and release of toxic hydrogen cyanide upon tissue disruption.

Tryptophan

· Alkaloides: provides protection as it prevents insects and herbivores eating the plant.

· Plant growth regulators

Diversity of bacteria according to nutritional requirments, temperature, Oxygen conditions and water activity

2012-01-18T07:52:00.000-08:00

Nutritional type	Energy source	Carbon source	Examples
Photoautotroph	Light	Inorganic carbon, i.e. CO₂	Some purple and green bacteria (Chromatium)
Photoheterotroph	Light	Organic compounds	Some purple and green bacteria (Rhodospirillum)
Chemoautotroph (Lithotroph, Lithoautotroph)	Inorganic compounds; H₂, H₂S, NH₃	CO₂	Many Archaea and few bacteria (Nitrosomanas)
Chemoheterotroph (Heterotroph)	Organic compounds	Organic compounds	Few Arcaea and many bacteria (Pseudomonas)

Type	Minimum (⁰C)	Optimum (⁰C)	Maximum (⁰C)
Psychrophile	Below 0	10-15	Below 20	Contain unsaturated fatty acids in plasma membrane to tolerate.
psychrotroph	0	15-30	Above 25	Able to grow at low T but prefer moderate T
Mesophile	10-15	30-40	Below 45	Most bacteria especially the ones associated with warm-blooded animals.
Thermophile	45	45-70	Above 100	Contain Saturated fatty acids in plasma membrane. High glucose and carbon content as well as high melting point for DNA.
Hyperthermophile	80	80-115	Above 115	Contain phytane and modified proteins in plasma membrane. High glucose and carbon content as well as high melting point for DNA.

Type	Aerobic condition	Anaerobic condition
Obligate aerobe	Growth	No growth
Microaerophiles	Growth; when the O₂ is at very low level	No growth
Obligate anaerobe	No growth; O₂is toxic	Growth
Facultative anaerobe/ facultative aerobe	Growth; Not essential to grow but utilized when available	Growth
Aerotolerant anaerobe	Growth; neither essential nor utilized	Growth

Type	Speciality
Halophile	Require NaCl for growth
Halo tolerant	Able to grow at moderate salt concentrations but grow best in the absence of NaCl
Osmophile	Able to grow in high levels of suger
Xerophile	Able to grow in dry conditions

Bonding in transition metal complexes:- Valence bond theory, Crystal field theory, Molecular orbital theory

2012-01-10T07:23:00.000-08:00

There are three theories of metal to ligand bonding in complexes.

Valence bond theory

Coordination compounds contain complex ions, in which ligands form coordinate bonds to the metal. Thus the ligand must have a lone pair of electrons, and the metal must have an empty orbital of suitable energy available for bonding. The theory considers which atomic orbitals on the metal are used for bonding. From this the shape and the stability of the complexes are predicted. The theory has two main limitations. Most transition metal complexes are coloured, but the theory provides no explanation for their electronic spectra. Further, the theory does not explain why the magnetic properties vary with temperature. For these reasons it has largely been superseded by the crystal field theory. However it is of interest for study as it shows the continuity of the development of modern ideas from Werner’s theory.

Crystal field theory

The attraction between the central metal and ligands in the complex is considered to be purely electrostatic. Thus bonding in the complex may be ion-ion attraction (between positive and negative ions such as Co³⁺and Cl^-). Alternatively, ion-dipole attractions may give rise to bonding (if the ligand is a neutral molecule such as NH₃ or CO). This theory has been remarkably successful in explaining the electronic spectra and magnetism of transition metal complexes. Particularly when allowance is made for the possibility of some covalent interaction between the orbitals on the metal and ligand. When some allowance is made for covelencey, the theory is often renamed as the ligand field theory. Three types of interaction are possible. The σ overlap of orbitals, π overlap of orbitals, or dπ – pπ bonding (back bonding) due to π overlap of full d orbitals on the metal with empty p orbitals on the ligands.

Molecular orbital theory

Both covalent and ionic contributions are fully allowed for in this theory. Though this theory is the probably the most important approach to chemical bonding, it has not displaced on the other theories. This is because the quantitative calculations involved are difficult and lengthy, involving the use of extensive computer time. Much of the qualitative description can be obtained by other approaches using symmetry and group theory.

Reference: Inorganic chemistry, J.D Lee

Preparation of solid derivatives of Carbonyl compounds (aldehydes & ketones) :- 2, 4- Dintrophenylhydrazones, Semicarbazones

2012-01-09T21:19:00.000-08:00

The systematic procedure that involves several steps and preparations is carried out to identify unknown compounds to some extent. The preparation of derivatives usually establishes the identification of the unknown with certainty. Here the term derivative is simply referred to a compound prepared from an unknown, in order to identify the unknown compound. An ideal derivative should be a crystalline, easily purified solid with a sharp melting point, which can be prepared readily from the unknown in one direct and unambiguous step.

Many carbonyl compounds can be synthesized from the esterification reaction. There are excellent and conveniently prepared derivatives which use to identify carbonyl compounds. Oximes, Phenyl hydrazones, 2, 4-dinitrophenylhydrazones and semicarbazones are some of the best derivatives of aldehydes and ketones. In the preparation of each of these types of derivatives, the elimination of a water molecule between a molecule of the carbonyl compound and a molecule of the reagent is involved.

Dinitrophenylhydrazine is relatively sensitive to shock and friction. It is a red to orange solid usually supplied wet to reduce its explosive hazard. This is often used as a qualitative test for carbonyl groups, associated with aldehydes and ketones. The hydrazone derivatives can be used as evidence toward the identity of the original compound. These are usually yellow-red colour crystals. Crystals of different hydrazones have characteristic melting and boiling points allowing the identification of the unknown substance.

Semicarbazone is one of the most commonly used derivatives to identify aldehydes and ketones. It is a derivative of an aldehyde or ketone formed by a condensation reaction between a ketone or aldehyde and the reagent; semicarbazide. As semicarbazides are not very stable in the free form, they are usually stored in the laboratory in the form of their hydrochloride salts. Many semicarbazones are off white, crystalline solids, useful for the identification of the parent carbonyl group by melting point analysis.

conductometric titrations

2012-01-08T03:58:00.000-08:00

In conductometric titrations, the electrical conductivity of an electrical solution is continuously monitored as one reactant is added. The accurate endpoint of can be determined by detecting a sudden change in the conductivity of the solution. It is particularly useful in titrating weak acids against weak bases. According to Ohm’s law;

I = E/R

Also,

R ∝ l

R ∝ 1/A

Therefore;

R = ρ l/A

ρ = RA/l

I = Current, E= electromotive force, R= Resistance, l = Length, A= cross section area, ρ= Resistivity

The reciprocal of resistivity is conductivity. It can be expressed as K.

K = 1/ ρ

= 1l / RA

= G l/A

G is the conductance.

In the titration, the conducting material is the solution. So the conductance depends on the type of ions in the solution and their concentration. If the solution is located between two electrodes at constant distance and cross section area, conductance will increase when the concentration of the solution decreases.

Also when l and A are constant it is clear that,

K ∝ G

These conditions can be obtained by using a conductivity cell that consisting a pair of platinum electrodes connected to the conductivity bridge which provides current to the cell. The meter will give out the calculated conductivity of the solution.

Nitration of acetanilide (Lab report)

2012-01-01T00:27:00.000-08:00

Introduction

Nitration is a type of chemical reaction which a nitro group is added to/substituted in a molecule. Basically it can be carried out by a mixture of concentrated nitric acid and sulphuric acid. Mixture is useful to obtain the active nitronium ion. Electrophilic aromatic substitution is a method used when a functional group is needed to be substituted on to an aromatic compound. In the nitration, nitronium ion acts as the electrophile that involves the attack of the electron-rich Benzene ring. In this experiment nitration is carried out using acetanilide.

Theory

Acetanilide displays moderately reactivity in electrophilic aromatic substitution. Also another advantage is, it’s not oxidized by nitric acid. Principally, acetanilide gives Ortho and Para mono nitroacetanilides. This position of nitronium ion is directed by the –NHCOCH₃ group attached to the benzene ring. This is due to the resonance delocalizing the benzene ring by nitrogen lone pair. Therefore Ortho and Para positions are more resonance stabilized than the Meta. Acetanilide undergoes ready nitration giving mainly the colourless P-nitroacetanilide, mixed with much smaller proportion of the yellow colour O-nitroacetanilide.

Procedure

· About 2g of powdered acetanilide and 2mL of Glacial acetic acid were mixed well in a 100mL beaker. 4mL of con.H₂SO₄ was added to the mixture.

· The beaker was placed in crushed ice until the temperature of the mixture was dropped down to 0-5⁰C.

· 4mL of con.H₂SO₄was added drop wisely while stirring the viscous mixture continuously keeping the temperature below 10⁰C.

· Afterwards the beaker was removed from the freezing conditions and allowed to stand 30 minutes at room temperature.

· The mixture was poured onto about 20g of crushed ice and stirred to obtain crystals. The beaker was rinsed with 10mL of water containing few fragments of ice and the solution was added to the main bulk of the product.

· It was allowed to stand for about 20minutes.

· Later it was filtered at the pump and washed thoroughly with cold water.

· Afterwards the crude product was recrystalized with water.

· Finally the melting point of the product was determined.

Observations

· Acetanilide powder was white in colour.

· Glacial acitic acid, H₂SO₄and acetanilide mixture was initially in pale yellow colour.

· In cold condition, white colour crystals were formed.

· Final purified crystals were also white.

· The determined melting point range was 150-152⁰C.

Conclusion

The initial compounds used were known. Therefore according to those the final product should be nitroacetanilide. As the colour of the product was white, it should be Para nitroacetanilide.

Discussion

Through the use of electrophilic aromatic substitution, acetanilide is nitrated to nitroacetanilide. There are several key steps involved in the nitration. The first step of the reaction involved in the donation of an electron pair by the acetanilide to the eletrophile, the nitronium ion. This nitronium ion was formed by the reaction of sulfuric and nitric acids. Basically the whole mechanism undergoes as below; (Benzene is shown here instead of acetanilide )

Image via en.wikipedia.org

To prevent dinitration of the acetanilide, the nitrating mixture of concentratred nitric acid and sulfuric acids were added in small portions to the acetanilide solution, so that the concentration of the nitrating agent is kept at minimum.

Also the addition of nitric acid is exothermic. Therefore the mixture would get too hot exceeding the temperature range suitable for the nitration. To avoid this, the addition of HNO₃ acid should be done very slowly, dropwisely.

Cold temperatures were used to slowdown the reaction rate and help to avoid over nitration.

Glacial acetic acid is used because it is a polar solvent capable of dissolving acetanilide and the acetate ion is a poor nucleophile, so no substitution is possible.

At the end, traces of acid should be removed because hydrogen ions catalyze the hydrolysis of the amide to p-nitroaniline. Acid is removed by pouring the mixture onto ice and water and filtering.

The melting point is determined to characterize the product. Theoretical melting point of the Para nitroacetanilide is found to be 214-216⁰C. The observed value was 150-152⁰C and it is much lower than the theoretical values and can be accounted for impurities in the product. Some impurities might be Ortho and Meta directing substances. Also there can be some experimental errors occurred during the experiment such as not controlling the exact temperatures mentioned for the reactions.

Controlling metabolism at cellular level: Compartmentation

2011-12-16T08:13:00.000-08:00

Metabolism is composed of reaction sequences termed as metabolic pathways. The changes at each step in a metabolic pathway are regulated in order to maintain the stability and survival of the organism. Mainly there are four ways of controlling metabolism. Such one important way of controlling metabolism at cellular level is compartmentation.

When considering a eukaryotic cell; it’s composed of many different compartments known as sub cellular organelles in contrast to a prokaryotic cell. Each organelle contributes a specific metabolic function with different enzymatic activities under different conditions. These metabolic pathways needed to be interconnected to maintain the metabolism. Therefore compartmentation allows the distribution of metabolites and enzymes between the membranes bounded organelles. It’s the method that enables the cell to obtain different metabolic activities at the same time for more energy efficiency. For an example, glycolysis occurs in the cytoplasm and provides the mitochondria substrates such as pyruvates from carbohydrate oxidation. TCA cycle occurs within the mitochondrion matrix while oxidative phosphorylation occurs in mitochondria inner membrane. However, altogether all these three processes are included in one metabolism called ‘cell respiration’. Enzymes of each process are found where the processes take place.

Fat metabolism is another one good example for compartmentation. Fatty acids synthesis takes place in cytoplasm. Cytoplasm contains the required enzymes for the anabolism of fatty acid synthesis. But these fatty acids are degregaded in mitochondria supplying Acetyl Co A for TCA cycle. Mitochondria also contain the enzymes require for the catabolism of fat.

RNA polymerase allows RNA synthesis by using a template of DNA strand. It catalyzes the synthesis of RNA. RNA synthesis takes place in nucleus. DNA transcription also occurs in nucleus. Therefore both the RNA polymerase and DNA templates are available, so that the RNA synthesis is favorable. When considering protein synthesis, all the organelles used for it are close to one another. The nucleolus makes ribosome which synthesizes proteins. Endoplasmic reticulum is near the nucleus to receive Ribosomes and synthesized proteins. The Golgi apparatus is also near the endoplasmic reticulum for storing, packaging and distribution. Therefore all the activities within a cell are cooperated with one another.

Hence, compartmentation helps metabolic controlling by maintaining substrates, regulators and enzymes in separate locations with only favoured access between them.

General facts of parasitic nematodes:- Pin worm, giant round worm, whip worm, pork worm, hook worm

2011-11-21T04:25:00.001-08:00

Enterobius sp.

image via human-healths.com

Common name: Pin worm/thread worm/ seat worm

Disease: Enterobiasis (symptoms:- itching in the preanal area)

Host: Human

Habitat: Small intestine

Infective stage: Eggs

Transmission: Ingesting eggs

Parasitic adaptations: Small, sticky, translucent eggs, cuticle

Enterobiu sp -Life cycle

Trichuris trichuira

image via plpnemweb.ucdavis.edu

Common name: Whip worm/tap wrom

Disease: Trichuriasis ( Symptoms: Diarrhea, anemia)

Host: Human

Habitat: Colon

Infective Stage: Embryonated eggs

Transmission: Ingesting eggs

Parasitic adaptations: Long slender tapered body, cuticle

Trichinella sp

image via human-healths.com

Common name: Pork worm

Disease: Trichinosis (Symptoms: nausea, diarrhea, vomiting, fever)

Host: Human, pig, bear, rat

Habitat: Intestine

Infective stage: Cysts (larva)

Transmission: Eating uncooked pork,

Parasitic adaptations: Long slender body, cuticle

image via dpd.cdc.gov

Ascaris sp

image via e-cleansing.com

Common name: Giant round worm

Disease: Ascariasis (Symptoms: Diarrhea, cough, nausea)

Host: Human

Habitat: Intestine

Infective stage: Embryonated eggs ( containing larva)

Transmission: Ingesting eggs

Parasitic adaptations: Long slender body, cuticle, lipid cover around the eggs which is resistant to abrasion and chemicals

Ancylostoma sp

image via plpnemweb.ucdavis.edu

Common name: Hook worm

Disease: Protein deficiency, anemia, cough

Host: Human, cat

Habitat: Intestine

Infective stage: Filari form larva

Transmission: Penetrating the intact skin of the host

Parasitic adaptations: Dental plates in mouth, slender body, cuticle

Plant senescence in brief

2011-08-12T08:49:00.000-07:00

Senescence

Senescence is an important program in which the function of a cell/tissue/whole plant naturally leads to its death.

Senescence involves in plant aging.

When tissues senesce they produce enzymes which can recycle the “expensive” materials and reroute the sub-units to somewhere else that growth takes place.

Overall senescence

· Occurs in the whole plant.

· Death takes place right after flower and setting.

· When the flower dies the whole plant dies too.

· Ex: Asteraceae ( Sun flower)

image via Wikipedia

Top senescence

· After the growth season the part above the ground dies remaining the underground part that can grow for several years.

· Therefore a rhizome is present.

· Ex: Weed, Grass

Deciduous senescence

· In dry seasons like winter and summer, the leaves falls and trunk remains.

· Leaves fall due to avoid the heavy transpiration occurs in the dry season.

· Ex: Deciduous plants

image via ehow.co.uk

Progressive senescence

· Older parts die due to the senescence and the new organs and tissues continue their development.

· Ex: Green trees

image via clasohm.com

As above mentioned, senescence can occur in cells as well as tissues.

Cell senescence

· Can be described according to the senescence in cell membrane and organelle level.

Senescence in cell membrane

Lipid phase change

· Plasma membrane has the fluid mosaic structure.

· This structure changes as the liquid crystalline state changes into the solid-gel state.

· Therefore the membrane gets inflexible and hard.

Degradation and preoxidation of lipids

· Lipid content gets decreased.

· It occurs as the lipid synthesis decreases and lipase content increases.

· Phospholipase, lipoxygenase, MDA and active O₂ content increase.

Increase in Phospholipase activity

· Mainly the activity of Phospholipase D takes place in plants.

Biomembrane degradation and leakage

· The equilibrium of ions breaks down.

· Metabolisms get disordered.

Senescence in organelle level

· Ribosomes and RER break down.

· Chloroplasts collapse and mitochondrion cristae are swollen.

· As the vacuoles break down, all the toxics inside them is released to the cell plasma.

· Therefore the autophagy takes place and the senescence of organelles activates.