Only 1 of 24 DNA strands used?

Bill_A_Nussbaumer at bd.com Bill_A_Nussbaumer at bd.com
Tue Jul 24 15:06:52 EST 2001


Despite the slightly condescending tone of the reply, Dr. Farrell is right
that your question seems to be using terminology incorrectly and is
probably thus confusing most "would be respondents".  The other explanation
is that you just haven't given us enough information in context to make
sense of your question.

I'm curious where you heard the statement.  ????

Perhaps, in addition to the information already given, you might be making
reference to what is commonly referred to as "junk DNA".  In short, junk
DNA refers to those areas of the genome that do not contain protein coding
genes.  These regions are estimated to make up some 97 - 99 percent of the
total DNA sequence in humans.  Keep in mind though that the term "junk DNA"
is quite possibly a misnomer.  A more accurate description would probably
be "DNA of unknown function". (Leaving open the possibility that some may
have no function at all.)

Regarding the number of chromosomes:  Although there are 23 pairs of
chromosomes in the cell, there are actually 24 different chromosomes in all
(22 autosomes plus 2 sex chromosomes -  X and Y).  Only males would carry
all 24 since females have no copy of the Y chromosome.

Regarding your use of the terminology "strand".  A DNA molecule consists of
two "strands", each strand is a linear series of nucleotide bases paired
with the opposite strand.  Therefore, each individual chromosome could be
said to contain two strands.  If you use this definition there would be 2
strands X 2 matching chromosomes (because, as described by Dr. Farrell,
humans are diploid and contain 2 copies of each chromosome) x 23
chromosomes = 92 strands comprised from 46 DNA molecules.  It's all
semantics really, but correct terminology is important for clear
communication.

By the way, all 24 of the chromosomes are actively used.

It might be interesting for you to see a representation of the genes
contained on the 24 different chromosomes here:
http://www.ncbi.nlm.nih.gov/cgi-bin/Entrez/maps.cgi?ORG=hum&MAPS=ideogr,loc&CHR=1

- Bill Nussbaumer



Sent by:  owner-microbio at hgmp.mrc.ac.uk


To:   microbio at hgmp.mrc.ac.uk
cc:
Subject:  Re: Only 1 of 24 DNA strands used?


Ron Newman wrote:

> I recently heard the statement "only 1 of  24 'strands' of  human DNA
> actively used".
>
> a)  Is this accurate?
> b) Is there a good reference on it?
> c) If true, are the 23 unused portions simply redundant systems, are they
> mutated, or do they
> have other potential function?

You have posted this question several times without receiving any replies.
In my opinion, the reason for the lack of response is related to a major
lack
of understanding of biology (human and otherwise) indicated in your post,
on
both the part of the person who made the statement to you and on your part.
A complete reply would (apparently) require a complete course in biology,
which no one is willing to provide.  Let me hit only the highest of the
high
points related to your question, leaving filling in of the details to you,
either by studying some basic biology texts or by asking questions of your
local high school or college biology teacher.

Human cells, except for germ (reproductive) cells, contain 23 pairs of
chromosome, with each chromosome consisting of 2 strands of DNA, thus there
are not 24 strands of DNA in a human cell but 46.  For each gene in each
chromosome, only one strand of the DNA comprising the gene is expressed,
with
the other strand being used primarily to dictate what sequence of bases
should be linked together to make a new "active" strand when the DNA is
replicated.  The active strand is not the same strand throughout a given
chromosome.  That is, for adjacent genes, opposite strands may be
expressed.

In a very small nutshell, then, the original statement made to you makes
absolutely no sense at all, for the reasons cited above and explained in
much
greater detail in a huge number of basic biology books available in any
library.

--
Larry D. Farrell, Ph.D.
Professor of Microbiology
Idaho State University





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