ZINC

The enzyme RNA polymerase, which is required for transcription, contains zinc and it is essential for protein bio synthesis.

Deficiency in Zinc leads to poor wound healing, lesions of skin impaired spermatogenesis, hyperkeratosis, dermatitis and alopecia

Enzymes are protein catalyst produced by a cell and responsible ‘for the high rate’ and specificity of one or more intracellular or extracellular biochemical reactions.

Enzymes are biological catalysts responsible for supporting almost all of the chemical reactions that maintain animal homeostasis. Enzyme reactions are always reversible.

The substance, upon which an enzyme acts, is called as substrate. Enzymes are involved in conversion of substrate into product.

Almost all enzymes are globular proteins consisting either of a single polypeptide or of two or more polypeptides held together (in quaternary structure) by non-covalent bonds. Enzymes do nothing but speed up the rates at which the equilibrium positions of reversible reactions are attained.

 In terms of thermodynamics, enzymes reduce the activation energies of reactions, enabling them to occur much more readily at low temperatures - essential for biological systems.

PROPERTIES OF TRIACYLGTYCEROLS

1. Hydrolysis : Triacylglycerols undergo stepwise enzymatic hydrolysis to finally liberate free fatty acids and glycerol.

The process of hydrolysis, catalysed by lipases is important for digestion of fat in the gastrointestinal tract and fat mobilization from the adipose tissues.

2. Saponification : The hydrolysis of triacylglycerols by alkali to produce glycerol and soaps is known as saponification.

3.Rancidity: Rancidity is the term used to represent the deterioration of fats and oils resulting in an unpleasant taste. Fats containing unsaturated fatty acids are more susceptible to rancidity.

Hydrolytic rancidity occurs due to partial hydrolysis of triacylglycerols by bacterial enzymes.

Oxidative rancidity is due to oxidation of unsaturated fatty acids.

This results in the formation of unpleasant products such as dicarboxylic acids, aldehydes, ketones etc.

Antioxidants : The substances which can prevent the occurrence of oxidative rancidity are known as antioxidants.

Trace amounts of antioxidants such as tocopherols  (vitamin E), hydroquinone, gallic acid and c,-naphthol are added to the commercial preparations of fats and oils to prevent rancidity. Propylgallate, butylatedhydroxyanisole (BHA)  and butylated hydroxytoluene (BHT) are the antioxidants used in food preservation.

Lipid peroxidation in vivo: In the living cells, lipids undergo oxidation to produce peroxides and free radicals which can damage the tissue. .

The free radicals are believed to cause inflammatory diseases, ageing, cancer , atherosclerosis etc

Iodine number : lt is defined as the grams (number)  of iodine absorbed by 100 g of fat or oil. lodine number is useful to know the relative

unsaturation of fats, and is directly proportional to the content of unsaturated fatty acids

Determination of iodine number will help to know the degree of adulteration of a given oil

Saponification number : lt is defined as the mg  (number) of KOH required to hydrolyse (saponify) one gram of fat or oiL

Reichert-Meissl (RM)  number: lt is defined as the number of ml 0.1 N KOH required to completely neutralize the soluble volatile fatty acids distilled from 5 g fat. RM number is useful in testing the purity of butter since it contains a good concentration of volatile fatty acids (butyric acid, caproic acid and caprylic acid).

Acid number : lt is defined as the number of mg of KOH required to completely neutralize free fatty acids present in one gram fat or oil. In normal circumstances, refined oils should be free from any free fatty acids.

IONIZATION OF WATER, WEAK ACIDS AND WEAK BASES

The ionization of water can be described by an equilibrium constant. When weak acids or weak bases are dissolved in water, they can contribute H+ by ionizing (if acids) or consume H+ by being protonated (if bases). These processes are also governed by equilibrium constants

Water molecules have a slight tendency to undergo reversible ionization to yield a hydrogen ion and a hydroxide ion :

H₂O = H⁺ + OH⁻

The position of equilibrium of any chemical reaction is given by its equilibrium constant. For the general reaction,

A+B = C + D

Ampholytes, Polyampholytes, pI and Zwitterion

Many substances in nature contain both acidic and basic groups as well as many different types of these groups in the same molecule. (e.g. proteins). These are called ampholytes (one acidic and one basic group) or polyampholytes (many acidic and basic groups). Proteins contains many different amino acids some of which contain ionizable side groups, both acidic and basic. Therefore, a useful term for dealing with the titration of ampholytes and polyampholytes (e.g. proteins) is the isoelectric point, pI. This is described as the pH at which the effective net charge on a molecule is zero.

For the case of a simple ampholyte like the amino acid glycine the pI, when calculated from the Henderson-Hasselbalch equation, is shown to be the average of the pK for the a-COOH group and the pK for the a-NH₂ group:

pI = [pK_a-(COOH) + pK_a-(NH3⁺₎]/2

For more complex molecules such as polyampholytes the pI is the average of the pK_a values that represent the boundaries of the zwitterionic form of the molecule. The pI value, like that of pK, is very informative as to the nature of different molecules. A molecule with a low pI would contain a predominance of acidic groups, whereas a high pI indicates predominance of basic groups.

IRON

The normal limit for iron consumption is 20 mg/day for adults, 20-30 mg/day for children and 40 mg/day for pregnant women.

Milk is considered as a poor source of iron.

Factors influencing absorption of iron Iron is absorbed by upper part of duodenum and is affected by various factors

(a) Only reduced form of iron (ferrous) is absorbed and ferric form are not absorbed

 (b) Ascorbic acid (Vitamin C) increases the absorption of iron (c) The interfering substances such as phytic acid and oxalic acid decreases absorption of iron

Regulation of absorption of Iron

Absorption of iron is regulated by three main mechanisms, which includes

(a) Mucosal Regulation

(b) Storer regulation

(c) Erythropoietic regulation

In mucosal regulation absorption of iron requires DM-1 and ferroportin. Both the proteins are down regulated by hepcidin secreted by liver. The above regulation occurs when the body irons reserves are adequate. When the body iron content gets felled, storer regulation takes place. In storer regulation the mucosal is signaled for increase in iron absorption. The erythropoietic regulation occurs in response to anemia. Here the erythroid cells will signal the mucosa to increase the iron absorption.

Iron transport in blood

The transport form of iron in blood is transferin. Transferin are glycoprotein secreted by liver. In blood, the ceruloplasmin is the ferroxidase which oxidizes ferrous to ferric state.

Storage form of iron is ferritin. Almost no iron is excreted through urine.

Anemia

Anemia is the most common nutritional deficiency disease. The microscopic appearance of anemia is characterized by microcytic hypochromic anemia

The abnormal gene responsible for hemosiderosis is located on the short arm of chromosome No.6.

The main causes of iron deficiency or anemia are

(a) Nutritional deficiency of iron (b) Lack of iron absorption (c) Hook worm infection (d) Repeated pregnancy (e) Chronic blood loss (f) Nephrosis (g) Lead poisoning