Ask A Scientist Molecular Biology Archive

name         Brianna
status       student
age          13

Question -   
What is the sugar phosphate supporting structure that holds up the double helix of dna?
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DNA is a polymer, or a molecule that is made of repeating units called monomers.  "Poly-" means 
"many", and "mono-" means "one". The suffix "-mer" means "part".  The monomer or single repeating 
unit of DNA is called a nucleotide.  Each nucleotide is made up of 3 subparts:  a sugar called 
deoxyribose, a phosphate group and a nitrogen base.  All nucleotides have the same sugar and 
phosphate, but there are 4 nitrogen bases:  adenine, guanine, cytosine and thymine.  So there 
are four different types of nucleotides.  The nucleotides are stacked one on top of the other with 
the phosphate and sugar groups alternating on the outside with the bases pointing at right angles 
from the sugar.  DNA is actually made of two strands of repeating nucleotides that are held together 
in the middle by hydrogen bonds.  So it kind of looks like a ladder with the steps of the ladder made 
up of a pair of nitrogen bases and the sides of the ladder made of alternating sugar and phosphate.  
Go to google.com and click on images, and search for DNA structure or DNA nucleotides.  You will 
find many pictures of what you are looking for.
 
vanhoeck
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