What enables these cells to perform specialized activities

Cellular function is determined by gene regulation. For example, a skeletal muscle cell has a set of genes turned on that are specific for that cell type. Each cell type has a unique set of genes involved in producing that type of cell. One can think of development as a system of gene switching, some on, some off, some up, some down. Up and down refer to the amount of the specific RNA being synthesized. In the past decade, we have had to broaden our concept of a gene since we sequenced the entire genome. We discovered that we have much more RNA molecules being involved with gene regulation than we originally imagined.

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