Page 223 - The Manga Guide to Biochemistry

Base complementarity and DNA structure

Nucleic acid consists of nucleotides connected in a long, linear chain. The car-
bons at the 3´ position and the 5´ position of each pentose link to a phosphate,
forming a bridge between individual nucleotides. This is called a polynucleotide.

NH2 N Looks kind of
N
A A like a comb!
P P P 5´

-O -O -O N N 4´ 1´
3´ 2´
-O P O P O P O CH2 O 5´ end
P 5´
OOO H H O CH3 4´
H H HN 5´
5´ end T 3´
H T or U
3´ P
(since it's O O N 1´
the end of O H 2´
the 5´ side) -O P O CH2
H 5´
O HH NH2
5´ N

H C

C

3´ O ON 4´ 1´
2´
-O P O CH2 O 3´

O H P
H
The five carbons are H 5´ G
numbered 1´ to 5´.* H

HO

5´ O HN N 4´ 1´
3´ 2´
4´ 1´ G
O H2N OH
N N

3´ 2´ -O P O CH2 O 3´ end
Deoxyribose
O H
* For the nucleotide saccharides, ´ (prime)
is appended to the numbers given to each HH H

OH H

carbon—for example, 1´, 2´, and so on—to

distinguish them from the numbers assigned

to the carbons in the nucleotide base. 3´ end (since it's the end of the 3´ side)

Polynucleotide

The bases form shapes that protrude like the teeth of a comb on one side of
the polynucleotide. For DNA, two polynucleotide strands form a double strand
by connecting these bases, which creates a helix structure.

Molecular Biology and the Biochemistry of Nucleic Acids 209