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Name: Tyler M.
Status: Student
Age: 16
Location: N/A
Country: N/A
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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