Organic Chemistry

Section 27.1 Nucleosides and Nucleotides 035

CH 3

H 2 N

2 ′-deoxyadenosine

N N

1 ′

3 ′ 2 ′

4 ′

5 ′

N N

NH 2

2 ′-deoxyguanosine

N N

HN N

O

2 ′-deoxycytidine

N

N

NH 2

O O

thymidine

N

HN

O

O

HO

O

HO

O

HO

O

HO

HO HO HO HO

3-D Molecules:

Bases; Nucleosides;

Nucleotides

Table 27.1 The Names of the Bases, the Nucleosides, and the Nucleotides

Base Nucleoside Ribonucleotide Deoxyribonucleotide

Adenine Adenosine Adenosine

Guanine Guanosine Guanosine

Cytosine Cytidine Cytidine

Thymine — Thymidine — Thymidine

Uracil Uridine — Uridine 5 ¿-phosphate

5 ¿-phosphate

2 ¿-Deoxycytidine 5 ¿-phosphate 2 ¿-Deoxycytidine 5 ¿-phosphate

2 ¿-Deoxyguanosine 5 ¿-phosphate 2 ¿-Deoxyguanosine 5 ¿-phosphate

2 ¿-Deoxyadenosine 5 ¿-phosphate 2 ¿-Deoxyadenosine 5 ¿-phosphate

PROBLEM 1

In acidic solutions, nucleosides are hydrolyzed to a sugar and a heterocyclic base. Propose

a mechanism for this reaction.

A nucleotideis a nucleoside with either the or the -OH group bonded in an
ester linkage to phosphoric acid. The nucleotides of RNA—where the sugar is
D-ribose—are more precisely called ribonucleotides, whereas the nucleotides of
DNA—where the sugar is 2-deoxy-D-ribose—are called deoxyribonucleotides.

When phosphoric acid is heated with it loses water, forming a phosphoanhy-
dride called pyrophosphoric acid. Its name comes from pyr, the Greek word for “fire.”
Thus, pyrophosphoric acid is prepared by “fire”—that is, by heating. Triphosphoric
acid and higher polyphosphoric acids are also formed.

P 2 O 5

nucleotides

adenosine 5′-monophosphate

a ribonucleotide

NH 2

N

N N

N

−O

O

O

O

HO OH

O−

P

2 ′-deoxycytidine 3′-monophosphate

a deoxyribonucleotide

NH 2

N

N

O

O

O

O−

O

O−

P

HO

5 ′-position

phosphate

group

3 ′-position

5 ¿- 3 ¿ nucleotide = base + sugar + phosphate