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 helix. The structure of the
double helix is somewhat like a ladder, with the base pairs forming the
ladder’s rungs and the sugar and phosphate molecules forming the vertical
sidepieces of the ladder.
An important
property of DNA is that it can replicate, or make copies of itself. Each strand
of DNA in the double helix can serve as a pattern for duplicating the sequence
of bases. This is critical when cells divide because each new cell needs to
have an exact copy of the DNA present in the old cell.
No comments:
Post a Comment