Essential Cell Biology 5th edition

78
PANEL 2–7 A SURVEY OF THE NUCLEOTIDES
BASES
O
NH 2
HC
HC
NH 2
C
C
N
H
N
C
cytosine
O
H 3 C
C
HC
thymine
HC
HC
O
C
T
N
H
C
U
N
H
NH
C
NH
uracil
C
O
O
5
6
The bases are nitrogen-containing ring
compounds, either pyrimidines or purines.
4
1
N
3
N
2
PYRIMIDINE
8
N
7
9
N
5
4
PURINE
6
3
N
1
N
2
adenine
HC
HC
guanine
N
N
N
H
N
H
C
C
C
C
N
O
C
N
C
A
G
N
CH
NH
C
NH 2
PHOSPHATES
The phosphates are normally joined to
the C5 hydroxyl of the ribose or
deoxyribose sugar (designated 5'). Mono-,
di-, and triphosphates are common.
O
– O P O CH2
O –
O O
– O P O P O CH 2
O – O –
O O
– O P O P O
O – O –
as in
AMP
O
as in
ADP
P O CH 2
O –
The phosphate makes a nucleotide
negatively charged.
as in
ATP
NUCLEOTIDES
A nucleotide consists of a nitrogen-containing
base, a five-carbon sugar, and one or more
phosphate groups.
PHOSPHATE
BASE
NH 2
O
– N
O P O CH2
O – 5′ O
4′ 1′
3′ 2′
Nucleotides
are the
OH OH
subunits of
SUGAR
the nucleic acids.
N
O
BASE–SUGAR
LINKAGE
N-glycosidic
bond
4′
5′
3′
O
SUGAR
2′
BASE
N
C
1′
H
The base is linked to
the same carbon (C1)
used in sugar–sugar
bonds.
SUGARS
HOCH 2
O
OH
PENTOSE
a five-carbon sugar
C 5’
Each numbered carbon on the sugar of a nucleotide is
followed by a prime mark; therefore, one speaks of the
“5-prime carbon,” etc.
O
4’ 1’
3’ 2’
two kinds of
pentoses are used
H
HOCH 2
H
H
OH
H
OH
O
H
H
OH
OH
H
H
H
β-D-ribose
used in ribonucleic acid (RNA)
β-D-2-deoxyribose
used in deoxyribonucleic acid (DNA)
Panel 2.07a