218

15

The Molecules of Life

Table 15.1 Atomic composition (selected elements) of a typical dried microbial cell

Element

Rel. atomic fraction

H

100 000100 000

C

5300

O

1600

N

1300

P

130

K, Na

80

S

40

Fe

5

Cu

1

Table 15.2 Molecular composition of a typical microbial cellSuperscript normal a^a

Molecule

wt (%)

mol (%)

upper M Subscript normal rMr Superscript normal b^b

No types

No molecules

DNA

1

–

3 times 10 Superscript 93 × 10⁹

1

1

RNA

6

–

(10 Superscript 510⁵)

500

250 000

Protein

15

–

5 times 10 Superscript 45 × 10⁴

1000

2 times 10 Superscript 62 × 10⁶

Saccharide

3

–

(10 Superscript 410⁴)

50

5000

LipidSuperscript normal c^c

2

0.1

10 cubed10³

40

2 times 10 Superscript 72 × 10⁷

SmallSuperscript normal d^d

2

1.0

10 squared10²

500

10 Superscript 710⁷

Water

70

98.9

18

1

2 times 10 Superscript 102 × 10¹⁰

Superscript normal a^aThe components are not uniformly dispersed in the cell

Superscript normal b^bParentheses indicate approximate means of very broad ranges

Superscript normal c^cIncluding liposaccharides

Superscript normal d^dMetabolic intermediates, inorganic ions, and so forth

Table 15.3 Some characteristics of the macromolecules of a cell

Polymer

Monomer

Monomer variety

Typical length

Bond varietySuperscript normal a^a

DNA

NucleotideSuperscript normal b^b

4

2000

1

RNA

NucleotideSuperscript normal b^b

4

2000

1

Protein

Amino acidSuperscript normal c^c

20

200

2

Polysaccharide

Monosaccharide

tilde 10∼10

20

tilde 3∼3

Superscript normal a^aThat is, the type of bonding between monomers

Superscript normal b^bA nucleotide consists of a base, a sugar, and one or more phosphate groups. The variety resides

solely in the bases

Superscript normal c^cAn amino acid consists of a backbone part, identical for all except proline, and a side chain (residue)

in which the variety resides