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200

3 Information: genes and genomes

H H

N

N

N

A

O

2’-deoxyribose

Unbonded hydroxyl (–OH) groups of phosphoric acid are negatively charged (–O – ) at cellular pH

N N

5’

O

–O

HO CH 2

OH

H

OH

P

Base

4’

1’

3’ 2’

H

H H

H

O–

H

HO

Phosphoric acid

H H N

2H 2 O

N

N

O

A

O

N N

–O

P

OCH 2

H

H H

H

O–

H

HO

Nucleotide (dAMP)

Glycosidic bond

Phosphoester bond

Figure 3.4 Bonding of the phosphate and base to 2 ′ -deoxyribose to form a nucleotide, deoxyadenosine monophosphate (dAMP). Note that while this figure gives useful information on nucleotide structure, simple condensation reactions with loss of water are not used to synthesize nucleotides in the cell. The figure also shows that nucleotides are negatively charged through loss of protons from the phosphates. Source : adapted from Watson et al. Molecular Biology of the Gene , 7th edn. Pearson. 2014.

Figure 3.5 The structures of the purine and pyrimidine bases found in DNA and RNA. The numbering of atoms making up the rings is shown. For each base the dotted line indicates the position at which formation of a glycosidic bond links the base to carbon 1 ′ of ribose or deoxyribose. Note that the only difference between the structure of thymine (found in DNA) and uracil (found in RNA) is the addition of a methyl group to carbon 5 in thymine. Adenine, guanine, and cytosine are found in both DNA and RNA. Source : adapted from Watson et al. Molecular Biology of the Gene , 7th edn. Pearson. 2014.

Purines

O C 6

C NH 2

N

N

6

NH

N

C

C

7

7

1 2

5 4

5 4

1 2

HC

HC

8

8

9

9

C

C

C

CH

3 N

3

N

N

NH 2

N

Adenine (A)

Guanine (G)

Pyrimidines

C O

C O 4

C NH 2

H 3 C

4

4

N

NH

NH

HC

C

HC

5 6

3 2

5 6

3 2

5 6

3 2

C

C

HC

HC

HC

1 N O C

N 1

N 1

O

O

Cytosine (C)

Thymine (T)

Uracil (U)

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