Name: Tyler M.
Date: March 2004
Why doesn't DNA take genetic information into the cytosol? Why
does it have to transfer it to mRNA?
Answer: Think of the DNA as a reference book or encyclopedia that may not be
taken out of the library - partly because it is too big and heavy, and
partly because other users will need to refer to the encyclopedia. They may
need to consult the same article you are interested in or another article.
When you find an article in the encyclopedia that you need to make use of,
you make a photocopy of just the pages you need or you sit in the library
and write your own notes to take with you.
DNA molecules are extremely large, too large to travel into the cytoplasm.
Each chromosome contains just one long, long molecule of DNA. Many genes are
found along the length of this one DNA molecule. When one of these genes
exerts its genetic control by producing a gene product, it does so by making
a copy of its genetic message in the form of mRNA. Some genes are constantly
making mRNA, in order to produce a constant supply of the protein gene
product. Other genes are transcribed into mRNA only occasionally or only in
certain cells of the body.
The mRNA is a small molecule, representing just one gene, not a whole
chromosome. The mRNA travels through the nuclear membrane to the cytoplasm,
where it is used to manufacture the protein product. Meanwhile the huge DNA
molecule remains behind in the nucleus and is available for making more mRNA
copies of the same gene and of the many other genes along its length.
Sarina Kopinsky, MSc, H.Dip.Ed.
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Update: June 2012