Chemical Composition of the Body
37
N
N
O
NH
2
C
O
H
C
C
OH
H
C
H
P
H
N
O
O
N
CH
2
O
Phosphate
Base (cytosine)
Sugar (ribose)
Typical ribonucleotide
NH
2
C
O
H
C
C
OH
H
C
H
P
H
H
O
O
CH
2
O
Phosphate
Base (cytosine)
Sugar (deoxyribose)
Typical deoxyribonucleotide
OH
O
O
O
(a)
(b)
Figure 2–22
Nucleotide subunits of DNA and RNA. Nucleotides are composed of a sugar, a base, and a phosphate group. (a) Deoxyribonucleotides present
in DNA contain the sugar deoxyribose. (b) The sugar in ribonucleotides, present in RNA, is ribose, which has an OH at a position in which
deoxyribose has only a hydrogen atom.
NH
2
N
N
N
N
CH
3
NH
2
N
N
O
O
NH
N
O
NH
N
NH
2
O
O
Uracil (RNA only)
Phosphate
Sugar
Nucleotide
Adenine (DNA and RNA)
Guanine (DNA and RNA)
Cytosine (DNA and RNA)
Thymine (DNA only)
O
N
HN
N
N
O
O
O
OPO
CH
2
O
O
OPO
CH
2
O
O
O
O
OPO
CH
2
O
O
O
O
OPO
CH
2
O
O
O
O
OPO
CH
2
O
Figure 2–23
Phosphate-sugar bonds link nucleotides in sequence to form nucleic acids. Note that the pyrimidine base thymine is only found in DNA, and
uracil is only present in RNA.
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