messenger RNA,Formation of structural and enzymatic proteins

Formation of structural and enzymatic proteins from messenger RNA (translation) which themselves are coded from genes by the process of transcription is the central feature of life releasing the information stored in the genome. Depending on the organismic complexity, the scheme varies and is regulated at various phases of execution by several proteins and short RNA molecules. In prokaryotes, where no separate compartment exists; for storing genome, transcription and translation is a coupled process and many a times common

regulatory meclianisnis are adopted by cell to coordinate the processes. In eukaryotic cellular environment genome is protected in separate envelope called nucleus where transcription takes place to generate mRNA. After import into cytoplasmic environment and several modifications, the processed mRNA is used as template for translation of polypeptides.

         Fourth and perhaps the most intriguing question relates to copying the information contained in the genome. Every organism, from single cell to complex multicellular animal or plant multiplies for propagation. When a cell multiplies through mitosis or produces gametes for sexual reproduction through meiotic

divisions, the genome is copied and distributed evenly in the progeny cells. Considering the linear nature of gene, there are about 30,000 genes in human genome which occupies only about 5% of the total genome. Each of the genes being several kilobases in size, the linear length of total genome would be more than one

meter. Being supercoiled as 24 (22 + X + Y) chromosomes in a nucleus of diameter of few micrometer only. the task of replicating the genome by untangling each of the chromosome and repacking them again in the form of chromosomes seems to be an Herculean task. The cell accomplishes this by exploiting the unique secondarij double helical structure of DNA, where two linear strands of polynucleotide (combination of pentose sugar, nitrogenous base and phosphate group) twist around each other and form hydrogen

bonding by complementary base pairing. Using the complementary nature, new DNA strands are synthesized and packed with one old strand so each new chromosome contains one old and one new strand in the double helix.