Biomolecules-IV

Synthesis of proteins - Transcription and Translation Transcription This is a process in which RNA is synthesized from DNA. Among the two strands of DNA one strand serves as template and is called as coding strand where as the other strand is called as non-coding strand as it does not participate in transcription. Transcription involves three different stages. Genetic Code Genetic code is the dictionary of nucleotide bases, which determines the sequence of amino acids in proteins. The genetic code (or) codons have triplet base sequences in m RNA, which act as code words for amino acids. The DNA sequence that code for a specific protein(or) polypeptide is called a gene. There are 4 different bases in m RNA - A, G, C and U. They produce 64 different triplets (43). Out of 64 codons 61 codons code for 20 amino acids. The 3 codons UAA, UAG and UGA do not code for amino acids and they are called non-sense codons. The codons AUG and GUG are called initiating codons. Mutation Mutation is defined as a chemical change in the DNA structure of a gene. A difference of a single base in the DNA molecule or a single error in the reading of the code can cause a change in the amino acid sequence which leads to mutation. Lipids Lipids are organic substances present in all living organisms. They include fats, oils, waxes and other related compounds. They are insoluble in water and hydrophobic, and soluble in organic solvents. They are related to fatty acids and are not polymers. They are esters of long chain fatty acids and alcohols. Hormones Hormones are the chemical messengers of the body. They are defined as organic substances secreted into blood stream to control the metabolic and biological activities. These hormones are involved in transmission of information from one tissue to another and from cell to cell. These substances are produced in small amounts by various endocrine (ductless) glands in the body. They are delivered directly to the blood in minute quantities and are carried by the blood to various target organs where these exert physiological effect and control metabolic activities. Thus frequently their site of action is away from their origin. Hormonesare required in trace amounts and are highly specific in their functions. The deficiency of any hormones leads to a particular disease, which can be cured by administration of that hormone. Introduction Vitamins are the organic compounds required for the normal maintenance and health of an organism in minute quantities and their absence cause specific deficiency diseases. These are required in diet in order to perform specific biological functions. There are about 15 vitamins essential for humans. Plants can synthesize cell vitamins whereas only a few are synthesized in animals and hence need to be supplied in the foods. Classification of Vitamins Fat soluble vitamins These vitamins are soluble in fats, oils and in fat solvents like alcohol, etc. There are four fat soluble vitamins. They are: Vitamin A, Vitamin D, Vitamin E and Vitamin K. Some Important Vitamins Vitamin A This is a fat soluble vitamin which is present mostly in animals. Its provitamins carotenes are found in plants. Vitamin A is necessary for vision and proper growth. It is necessary for maintenance of proper immune system to fight various infections. Cholesterol synthesis requires vitamin A. The carotenoids act as antioxidants and reduce risk of cancers. Functions of Vitamins in Biosystems Vitamins are the important food factors required in diet. Different vitamins are involved in different biochemical functions. They are required in very low concentration, the daily requirement of any vitamin for any individual is extremely smell. The daily dose of any vitamin is not a fixed quantity but varies according to size, age and rate of metabolism of the individual. Youngsters need higher quantity of vitamins then elders and their requirement increases when a person performs exercise. Growing children and pregnant mothers need more quantity of vitamins in their diet.