Base pairs hold the actual
information in
DNA and
RNA -- somewhat analogous to pits on a
CD, or the magnetic coating on a
hard disk. Each
DNA nucleotide is made up of a
sugar molecule, (
S, below) a molecule of
phosphoric acid (
P), and another molecule (technically either a
purine or
pyrimidine) called the
base. DNA bases are
Adenine,
Guanine,
Thymine, or
Cytosine; in
RNA uracil replaces thymine. Each base pairs up with its opposite in a
DNA molecule,
guanine with
cytosine,
adenine with
thymine, to form base pairs. Guanine-cytosine base pairs have two
hydrogen bonds, while adenine-thymine pairs have three -- an excellent picture of this is available in
jafuser's writeup under
DNA.
Here is what each base pair would look like on a flattened strand of DNA:
base pair
_|_
P / \ P
- /
S--A T--S
/ -
P P
- /
S--G C--S
/ -
P P
- /
S--T A--S
/ -
P P
- / _
S--C G--S \
/ - } nucleotide
P P _/
Insertion of the wrong base in a piece of DNA while it is being replicated is a mutation referred to as a base pair substitution. In most cases this causes there to be an incorrect amino acid to be inserted into the protein coded for by the effected gene, which may or may not hinder the function of the protein. Every once in a while, a base pair substitution will change the effected codon from coding for an amino acid to being a stop codon. When this happens, the protein that would've been made by the gene is only partially complete, and is most likely useless.