Flow of Information
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Flow of Information
Structure of Cell of Class 11
Cells require information for regulating their activities. There are two types of information:
(a) Intrinsic Information : Contained in each and every cell as genetic information coded inside DNA molecules. The code consists of sequence of nitrogen base in triplets called genetic code. One base triplet determines one amino acid of a polypeptide chain.
Depending upon specific triggers, DNA molecules open at specific points and transcribe the information to mRNA molecules in the form of complementary base triplets. mRNA molecules pass into the
cytoplasm and get associated with ribosomes where, they translate the information by directing the amino acids to join in a particular sequence according to base triplets. Thus, an intrinsic polypeptide is
synthesised.
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Fig. Flow of information into a cell
The flow of intrinsic information from DNA to mRNA and then to polypeptide is often called central dogma of molecular biology.
Polypeptides get transformed into particular proteins and enzymes.
(b) Extrinsic Information : Comes from outside in the form of specific stimuli and information molecules. Stimuli are commonly brought by nerves. The nerves secrete specific chemicals that stimulate
particular systems of the cells. Information molecules are commonly hormones, which act in two ways:
(i) Within the Cell : Some of the hormones are able to pass into the cells, where they combine with specific intracellular receptors. The latter carry the hormones to the nucleus where they function as an inducer
by removing the repressor of particular genes. The activated genes transcribe specific mRNAs for synthesis of particular proteins and enzymes inside the cytoplasm.
(ii) Cell Surface : The hormones do not enter the cells, instead, they combine with membrane receptors. The hormone-receptor complex can function in two ways
(a) It may change the membrane permeability e.g. opening of calcium channels. On entering a cell, calcium combines with protein calmodulin. The activated protein has multiple effects.
(b) Through the formation of second chemical messenger like cyclic AMP. cAMP activates an enzyme system already present in the cell.
