Histone modification: a. can change over time in response to environmental cues, but this has no effect on gene expression. b. is fixed; once a histone is modified, it stays that way and the genes with which it is associated are turned on or off permanently. c. is random; sometimes the lysines are are modified and sometimes they're not, but the state is independent of the environment or cell type. d. is fixed, but this has no effect on whether genes are expressed. e. can change over time in response to environmental cues, allowing genes to be turned on or off as needed.

The best answer to the question: Histone modification:___, would be: E: Can change over time in response to environmental cues, allowing genes to be turned on or off as needed.

Explanation:

Unlike what it would be believed, that cells are always in a constant state of gene expression, differentiation and cell modification, research has shown that this process is highly dependent on the environment on which a cell may be, even stem cells, and the availability of nutrients. This means that whenever a cell is in an environment that does not motivate proliferation, or differentiation, gene expression can be halted, and the entire process can be halted as well, until better conditions are reached. Science, however, cannot yet explain exactly how, when an environment becomes positive for genetic expression, and cell proliferation, the cell activates its gene expression. What is known is that the process begins by the acetylation of histones thanks to an incrase in acetyl-CoA when nutrients become available again.

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