The Foundations of Chemistry

The two carbohydrates in nucleic acids are ribose (contained in RNA) and 2-deoxyribose
(contained in DNA); these carbohydrates differ in the presence or absence of an oxygen
atom on carbon 2.

The bases found in nucleic acids are shown in Figure 28-17. Each type of nucleic acid
contains two pyrimidine bases and two purine bases. The two purine bases adenine (A)
and guanine (G) and the pyrimidine base cytosine (C) are found in both RNA and DNA.

O OH

HO

H

H

H

H

H

2

4

3

1

HOCH 2

5

2-deoxyribose

O OH

HO OH

H

H

H

H

HOCH 2

5

2

4

3

1

ribose

28-10 Nucleic Acids 1135

• O

O

P

O–

OCH 2 O

C

H

C

H

H

C

OH

H

C

H

H

H

N

N N

N

NH 2

base

carbohydrate group

phosphate group

HO P O

O

CH 2

C

H

H

O

C

O

H

C

C

H

H

P

O

CH 2

C

HO O

O

C

H

C

H C

HH

O H

P

O

HO O

Base

Repeating

unit along

DNA

chain

Base

N

N

N

N

H

NH 2

NH 2 N N

H

HN N

O

N

H

HN

O

O

NH 2

O N

H

N

O

N

H

O

CH 3

HN

Purine bases Pyrimidine bases

adenine (A)

DNA

RNA

guanine (G)

DNA

RNA

uracil (U)

RNA

cytosine (C)

DNA

RNA

thymine (T)

DNA

Figure 28-16 A short segment of

DNA (deoxyribonucleic acid).

Figure 28-15 The three kinds of units that are polymerized to form nucleic acids.

Figure 28-17 The bases found in DNA and RNA.