10Regulation of Gene Expression

The bacterium Escherichia coli has approximately 4300 genes, while human cells possess approximately 25,000 genes. Every gene is not always expressed, and gene expression is regulated. Genes required for a cell to survive and proliferate are called house-keeping genes, and both unicellular prokaryotes such as E. coli and multicellular eukaryotes such as humans share a similar mechanism of gene expression regulation. In addition, multicellular eukaryotes such as humans also possess genes involved in cell differentiation. A structure called chromatin, which is only found in eukaryotes, is involved in the regulation of gene expression associated with cell differentiation. Heterochromatin is a tightly packed form of chromatin in which gene expression is inactive, while euchromatin is a loosely packed form of chromatin that contains active genes capable of expression. Gene expression is affected by changes in chromatin structure and by binding of transcriptional regulatory factors according to the variable cell environment.

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