Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne DNA Structure
Name: Brianna 
Status: Student
Age: 13
Location: N/A
Country: N/A
Date: March 2004

What is the sugar phosphate supporting structure that holds up the double helix of dna?

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 and click on images, and search for DNA structure or DNA nucleotides. You will find many pictures of what you are looking for.


Click here to return to the Molecular Biology Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (, or at Argonne's Educational Programs

Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory