What is DNA? - Genetics Home Reference

Skip Navigation

Genetics Home Reference: your guide to understanding genetic
conditions About   Site Map   Contact Us

Search [INPUT] 

Home A service of the *U.S. National Library of Medicine®*
· Home
· Conditions
· Genes
· Chromosomes
· Handbook
· Glossary
· Resources


· Table of Contents

· Cells and DNA
· How Genes Work
· Mutations and Health
· Inheritance
· Consultation
· Testing
· Therapy
· Human Genome Project
· Genomic Research

Turn PageNext
Handbook > Cells and DNA >

** What is DNA? **

DNA, or deoxyribonucleic acid, is the hereditary material in humans and
almost all other organisms. Nearly every cell in a person’s body has the
same DNA. Most DNA is located in the cell nucleus (where it is called
nuclear DNA), but a small amount of DNA can also be found in the
mitochondria (where it is called mitochondrial DNA or mtDNA).

The information in DNA is stored as a code made up of four chemical bases:
adenine (A), guanine (G), cytosine (C), and thymine (T). Human DNA consists
of about 3 billion bases, and more than 99 percent of those bases are the
same in all people. The order, or sequence, of these bases determines the
information available for building and maintaining an organism, similar to
the way in which letters of the alphabet appear in a certain order to form
words and sentences.

DNA bases pair up with each other, A with T and C with G, to form units
called base pairs. Each base is also attached to a sugar molecule and a
phosphate molecule. Together, a base, sugar, and phosphate are called a
nucleotide. Nucleotides are arranged in two long strands that form a spiral
called a double

Source: ghr.nlm.nih.gov/handbook/basics/dna

what is dna

DNA - Wikipedia, the free encyclopedia


** DNA **

From Wikipedia, the free encyclopedia
Jump to: navigation, search
For a non-technical introduction to the topic, see Introduction to
For other uses, see DNA (disambiguation).
Page semi-protected
The structure of the DNA double helix. The atoms in the structure are
colour-coded by element and the detailed structure of two base pairs are
shown in the bottom right.
The structure of part of a DNA double helix

*Deoxyribonucleic acid* (*DNA*) is a molecule that encodes the genetic
instructions used in the development and functioning of all known living
organisms and many viruses. Along with RNA and proteins, DNA is one of the
three major macromolecules essential for all known forms of life. Most DNA
molecules are double-stranded helices, consisting of two long biopolymers
of simpler units called nucleotides—each nucleotide is composed of a
nucleobase (guanine, adenine, thymine, and cytosine), recorded using the
letters G, A, T, and C, as well as a backbone made of alternating sugars
(deoxyribose) and phosphate groups (related to phosphoric acid), with the
nucleobases (G, A, T, C) attached to the sugars. DNA is well-suited for
biological information storage, since the DNA backbone is resistant to
cleavage and the double-stranded structure provides the molecule with a
built-in duplicate of the encoded information.

The two strands of DNA run in opposite directions to each other and are
therefore anti-parallel, one backbone being 3′ (three prime) and the
other 5′ (five prime). This refers to the direction the 3rd and 5th
carbon on the sugar molecule is facing. Attached to each sugar is one of
four types of molecules called nucleobases (informally, /bases/). It is the
sequence of these four nucleobases along the backbone that encodes genetic
information. This information is read using the genetic code, which

Source: en.wikipedia.org/wiki/DNA

© 2005-2018 HaveYourSay.org