Ganong's Review of Medical Physiology, 23rd Edition

12 SECTION ICellular & Molecular Basis of Medical Physiology

FIGURE 1–10 Basic structure of nucleotides and nucleic acids. A) At left, the nucleotide cytosine is shown with deoxyribose and at right
with ribose as the principal sugar. B) Purine bases adenine and guanine are bound to each other or to pyrimidine bases, cytosine, thymine, or uracil
via a phosphodiester backbone between 2'-deoxyribosyl moieties attached to the nucleobases by an N-glycosidic bond. Note that the backbone
has a polarity (ie, a 5' and a 3' direction). Thymine is only found in DNA, while the uracil is only found in RNA.

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–

OPOCH 2

OO

O–

OPOCH 2

O

O

O

O–

OPOCH 2

O

O

O

O–

OPOCH 2

O

O

O

O–

OPOCH 2

O

A

B

N

N –O

NH 2

C

O

H

C

C

OH

H

C

H

P

H

N

O CH 2 N O

O

Phosphate

Base (cytosine)

Sugar (ribose)

Typical ribonucleotide

NH 2

C

O

H

C

C

OH

H

H C

P

H

H

O CH 2 O

O

Phosphate

Base (cytosine)

Sugar (deoxyribose)

Typical deoxyribonucleotide

OH

O–

–O

O–