Internal State and Gene Expression
A gene is a segment of the long thin molecule of DNA. Each gene encodes a protein or part of a protein. The proteins perform all the numerous activities of life. They are directly or indirectly responsible for all the cell’s structures, its organisation, its metabolism, its transport processes, and the co-ordination of these: in short, its internal state. Genes themselves do nothing except encode proteins. To make any given protein, the appropriate gene is copied on to a messenger RNA and then this copy is read by ribosomes, which translate the coded instructions. When a cell reproduces, the replicating machinery has to ensure that each of the two daughter cells receives an exactly identical copy of the parent cell’s DNA. Both daughter cells must have all and only the same genes as the parent cell so that they are potentially capable of making all (and only) the same proteins as the parent cell.
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