DNA basics

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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 shows four main building blocks. We call these nitrogenous bases: Adenine (A), Thymine (T), Guanine (G), and Cytosine (C). DNA also includes sugars and phosphate groups (made of phosphorus and oxygen). These make the phosphate-deoxyribose backbone.

If you think of the structure of DNA as a ladder, the rungs of the ladder (where you would put your hands) 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 copy all or part of the DNA.

DNA Shape

Aritist representation of DNA

The most common DNA shape illustrated by artists and scientists looks a lot like a twisting ladder. Scientists 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 (almost two meters).

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 new phosphate backbone, to create two new copies of DNA. Each single strand then pairs with a correct complementary base to create a new double-stranded piece of DNA. The copies will match because only "A" pairs with "T" and only "G" pairs 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: June 12, 2024
  • Link: https://askabiologist.asu.edu/dna-shape-and-structure

APA Style

Dr. Biology. (2010, April 24). DNA Structure and Shape. ASU - Ask A Biologist. Retrieved June 12, 2024 from https://askabiologist.asu.edu/dna-shape-and-structure

American Psychological Association. For more info, see http://owl.english.purdue.edu/owl/resource/560/10/

Chicago Manual of Style

Dr. Biology. "DNA Structure and Shape". ASU - Ask A Biologist. 24 April, 2010. https://askabiologist.asu.edu/dna-shape-and-structure

MLA 2017 Style

Dr. Biology. "DNA Structure and Shape". ASU - Ask A Biologist. 24 Apr 2010. ASU - Ask A Biologist, Web. 12 Jun 2024. https://askabiologist.asu.edu/dna-shape-and-structure

Modern Language Association, 7th Ed. For more info, see http://owl.english.purdue.edu/owl/resource/747/08/
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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