Gene Regulation - 1 Regulating Genes We have been discussing the structure of DNA and that the information stored in DNA is used to direct protein synthesis. We've studied how RNA molecules are used to transcribe and translate DNA information to direct the synthesis of specific proteins. We have also discussed briefly how mutations alter DNA sequences and can affect gene expression. We also know that each cell of an organism has exactly the same DNA, yet we have many different types of cells and tissues within a multicellular organism. For example, more than 20,000 genes have been identified in the human genome, but only a small portion of those genes are expressed in any given cell. The process of cell differentiation, in which cells become specialized for their specific function, involves selectively activating some genes and repressing others. Many genes in multicellular organisms are activated only at one stage of development, do their job, and function no more. The effects of these genes are not reversible. How does a cell " "know" what DNA is needed and when?
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