Basics of DNA

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Chromosome: a long, thread-like molecule made of the chemical called DNA (deoxyribonucleic acid) that is held together with special proteins and is visible (with strong microscopes) during cell division... more

Molecule: a chemical structure that has two or more atoms held together by a chemical bond. Water is a molecule of two hydrogen atoms and one oxygen atom (H2O)... more

DNA Structure

Chemical stucture of DNA

Image by Madprime via Wikimedia Commons.

A closer look at the chemical structure of DNA includes the four nitrogenous bases Adenine (A), Thymine (T), Guanine (G), and Cytosine (C). DNA also includes sugars and phosphate groups that make the phosphate-deoxyribose backbone.

If you think of the structure of DNA as a twisted ladder, the rungs of the ladder are made from the nitrogenous bases. These bases pair up to make each step of the ladder. They also only pair up in a specific way. (A) always pairs with (T) and (G) always pairs with (C). This is very important when it is time to duplicate all or part of the DNA.

To make a copy, the DNA only needs to unzip the bases into single strands. Each single strand then pairs with the correct complimentary base to create a new double-stranded piece of DNA.

DNA Shape

Aritist representation of DNA

The most common DNA shape illustrated by artists and scientist looks a lot like a twisting ladder. Scientist call this a double helix.  DNA also folds and coils itself into more complex shapes. The coiled shape makes it very small. In fact, it is small enough to easily fit inside any of our cells. This is a pretty amazing feat when you find out that the DNA from one cell, if unfolded, would stretch out to a length of six feet.

DNA replication

DNA does more than store information. It is also able to make copies of itself. To do this it first has to unzip the nitrogenous bases. All the pairs of "AT" and "GC" are separated. The DNA then has two single strands. At this point new pairs are made along with a phosphate backbone to create two new copies of DNA. The copies will match because only "A" pairs with "T" and "G" pairs only with "C".


Additional images by NIH.

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Bibliographic details:

  • Article: DNA Structure and Shape
  • Author(s): Dr. Biology
  • Publisher: Arizona State University School of Life Sciences Ask A Biologist
  • Site name: ASU - Ask A Biologist
  • Date published: April 24, 2010
  • Date accessed: January 18, 2019
  • Link:

APA Style

Dr. Biology. (2010, April 24). DNA Structure and Shape. ASU - Ask A Biologist. Retrieved January 18, 2019 from

American Psychological Association. For more info, see

Chicago Manual of Style

Dr. Biology. "DNA Structure and Shape". ASU - Ask A Biologist. 24 April, 2010.

MLA 2017 Style

Dr. Biology. "DNA Structure and Shape". ASU - Ask A Biologist. 24 Apr 2010. ASU - Ask A Biologist, Web. 18 Jan 2019.

Modern Language Association, 7th Ed. For more info, see
Human spectral karyotype
Human chromosomes coiled into their compact shape. Each pair of chromosomes has been colored to make it easier to identify.


How can the environment affect DNA? Learn more at Ask An Anthropologist's story Controlling the Code.


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