DIAMSAY, ELISHA GRACE B.
MENDOZA, LINETTE M.
to help visualize
the structure of
James D. Watson and Francis
Crick, co-originators of the double-
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.
Where is it located?
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
DNA stores an organism's genetic
information and controls the
production of proteins and is thus
responsible for the biochemistry of
• The structure of DNA is
illustrated by a right
handed double helix, with
about 10 nucleotide pairs
per helical turn
• Each spiral
strand, composed of a
backbone and attached
bases, is connected to a
complementary strand by
hydrogen bonding (non-
covalent) between paired
bases, adenine (A) with
thymine (T) and guanine
(G) with cytosine (C).
Adenine forms 2
Guanine forms 3
Sugar - Either ribose or deoxyribose (in RNA or DNA).
Purines consist of a six-membered and a five-
membered nitrogen-containing ring, fused together
Pyridmidines have only a six-membered nitrogen-
– Uracil (RNA)
Phosphates - One to three, two of which are usually
hydrolyzed to provide the energy to attach the
nucleotide and form the phosphodiester bond.
Base Pairing of DNA
• In a DNA double helix, each type of
nucleobase on one strand normally interacts
with just one type of nucleobase on the other
strand. This is called complementary base
• Purines form hydrogen bonds to
pyrimidines, with A bonding only to T, and C
bonding only to G.