Genes don’t simply produce their products at a steady, incessant pace, like a 24-hour nonstop manufacturing plant. They are turned on and off from day to day, even hour to hour,

as their products are needed or not, and many genes are permanently turned off in any given cell. The genes for hemoglobin and digestive enzymes, for example, are present but inactive in liver cells and skin cells.

There are several ways to turn genes on or off. We can’t consider all of them here, but an example can convey the general principle. Consider a woman who has just given birth to her first baby

In the ensuing days, the hormone prolactin stimulates cells of her mammary glands to synthesize the various components of breast milk, including the protein casein—something her body has never synthesized before.

This binding enables RNA polymerase to bind to the gene and transcribe it, producing the mRNA for casein.

At step 4, there are multiple ways that regulatory proteins can activate gene transcription.

Some of them attract and position RNA polymerase so it can begin transcribing the gene.

Others modify the coiling of DNA in a nucleosome in a way that makes specific genes more accessible to RNA polymerase.

To turn off a gene, a regulatory protein or ncRNA can coil the chromatin in a different way that makes the gene less accessible,

thus preventing transcription. Moving the chromatin over to the nuclear lamina is another way of silencing some of its genes.

There are several additional ways, beyond the scope of this book, for inducing or halting the production of a gene product but the casein example shows how a certain gene may lie dormant in a person until,

only a few times in one's life (and only if one bears children), it is activated by a stimulus such as a hormonal signal. Section 4.4h describes a further aspect of gene regulation called epigenetics.

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4.2e

Question	Answer
Genes don’t simply produce their products at a steady, incessant pace, like a 24-hour nonstop manufacturing plant. They are turned on and off from day to day, even hour to hour,	as their products are needed or not, and many genes are permanently turned off in any given cell. The genes for hemoglobin and digestive enzymes, for example, are present but inactive in liver cells and skin cells.
There are several ways to turn genes on or off. We can’t consider all of them here, but an example can convey the general principle. Consider a woman who has just given birth to her first baby	In the ensuing days, the hormone prolactin stimulates cells of her mammary glands to synthesize the various components of breast milk, including the protein casein—something her body has never synthesized before.
This binding enables RNA polymerase to bind to the gene and transcribe it, producing the mRNA for casein.	At step 4, there are multiple ways that regulatory proteins can activate gene transcription.
Some of them attract and position RNA polymerase so it can begin transcribing the gene.	Others modify the coiling of DNA in a nucleosome in a way that makes specific genes more accessible to RNA polymerase.
To turn off a gene, a regulatory protein or ncRNA can coil the chromatin in a different way that makes the gene less accessible,	thus preventing transcription. Moving the chromatin over to the nuclear lamina is another way of silencing some of its genes.
There are several additional ways, beyond the scope of this book, for inducing or halting the production of a gene product but the casein example shows how a certain gene may lie dormant in a person until,	only a few times in one's life (and only if one bears children), it is activated by a stimulus such as a hormonal signal. Section 4.4h describes a further aspect of gene regulation called epigenetics.

Created by: Russells3709

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