Ask A Scientist Molecular Biology Archive

name        Dana
status       student
age          14

Question -   
1.In which direction is the DNA molecule spiralled?
2. How many bases are included in each twist of the DNA molecule?
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The Watson and Crick structure of DNA  sometimes called B-DNA...yes there
are different forms of DNA...the real story in biology is always more
complex...this is the most recognized form of DNA, partly because the
pattern it produces in images using x-rays resembles the DNA we find in
sperm. This being said, here are some of the dimensions of B-DNA


*         It is considered right handed...its helix is right handed..no arms
, no legs

*         Its diameter across the helix is about 20 angstroms

*         It has ten base pairs for every complete twist of the double helix

Which if you do your simple 8th grade math that between each set of base
pairs on the helix there are 36 degrees of rise per turn ...10 time 360
equals a complet twist...get it?

*         The helix has a rise of 34 angstroms for every complete 360
degrees of turn

*         Since the helix is not the simplest twist that is often shown in
secondary school books of cheap models, but what I think of as a helix upon
a helix, the indentations of the helix are unequal and there is a deep or
major groove and a shallow or minor groove.  For a decent model go to
http://www.biochem.uwo.ca/meds/medna/doublehelix.html
 

pf
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Actually, DNA can form two right-handed helix shapes (called A and B)
and one left-handed helix shape (called Z).  In cells, the B-form is the
most common.  It is a right-handed helix that has approximately 10 bases
per turn of the helix.  

Christopher Perkins
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The DNA molecule is more specifically called a helix which is a spiral 
with a constant diameter. It is a right handed helix which means the helix 
rotates in a clockwise direction as it moves away from your eye. There are 
exactly 10 base pairs for each turn of the helix. For examples of left 
handed helices that were printed by mistake, go to 

www.lecb.ncifcrf.gov/~toms/Leftwhole.html 

Ron Baker, Ph.D.
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The DNA is double stranded.  One strand spirals one way and the other  strand 
spirals the opposite way.  The strands are said to be  antiparallel.  There 
are 10 bases in each turn of the helix.
 
vanhoeck
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