biology question #1657



Diana, a 20 year old female from Tucson asks on October 26, 2003,

Q:

How large is a human genome? What percentage of the DNA in the Human Genome actually codes for genes?

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the answer

Barry Shell answered on October 26, 2003, A:

According to an article in Salon, from 2001, there are 3.2 Billion base pairs in DNA. In other words, over three billion "letters" make up the "document" that describe the genetic makeup of a human being. Scientists used to think that these would code for over 100,000 genes, but after the human genome was decoded and published in February of 2001, it turns out there are only about 30,000 to 40,000 genes. Most of the rest of the genetic material in DNA is so called "junk DNA" or "jumping DNA" that does not appear to code for any sort of protein. Only about 1 - 1.5% of our DNA holds the instructions for making proteins. We normally think of genes as coding for proteins, molecules which then go on to form membranes, cells, and organs. A big outstanding mystery in genetics concerns the purpose of the other 99% of our DNA that does not seem to code for any particular thing.

Barry Shell answered on June 3, 2008, A:
In the five years since this question was first answered much more has been learned about so-called "Junk DNA". In particular it codes for small molecules of RNA that regulate the transcription of DNA that codes for genes. This regulation occurs in numerous ways. In fact, more DNA codes for this regulatory RNA than for genes themselves.
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