MadSci Network: Cell Biology

Re: How do cells 'know' not to use genes that do not apply to them?

Date: Fri Apr 16 14:18:42 1999
Posted By: Pamela Norton, faculty, Dept. of Medicine, Thomas Jefferson Univ.
Area of science: Cell Biology
ID: 916580427.Cb

As you might expect, it's rather complicated and the process is not 
understood completely. However, turning a gene on involves recruiting a lot 
of proteins (called transcription factors) to a small region of DNA at one 
end of the gene. Some genes can only be turned on when a specific 
combination of factors is present, and this combination only occurs in 
certain cell types. These genes are "off" in all other cells.  

There are other aspects to turning genes on and off, however. DNA normally 
is packaged up with a lot of proteins inside of the cell's nucleus. The way 
the DNA is packaged can prevent the transcription factors from finding a 
gene. The organization of genes along the DNA strand can determine whether 
a given gene is wrapped up and hidden away (off), or whether it remains 
accessible to transcription factors (on). Thus, genes are controlled by 
more than one mechanism.

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