Carbon and the Molecular Diversity of Life

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5

5-Methyl cytidine is a

component of DNA that has

been modified by addition of

the methyl group.

In addition to taking part in

many important chemical

reactions in cells, glycerol

phosphate provides the

backbone for phospholipids,

the most prevalent molecules in

cell membranes.

Glycerol phosphate

Cysteine

Cysteine is an important

sulfur-containing amino

acid.

Glycine

Because it also has a

carboxyl group, glycine

is both an amine and

a carboxylic acid;

compounds with both

groups are called

amino acids.

Addition of a methyl group

to DNA, or to molecules

bound to DNA, affects

expression of genes.

Arrangement of methyl

groups in male and female

sex hormones affects

their shape and function.

Contributes negative charge

to the molecule of which it is

a part (2– when at the end of

a molecule; 1– when located

internally in a chain of

phosphates).

Has the potential to react

with water, releasing energy.

Two sulfhydryl groups

can react, forming a

covalent bond. This

“cross-linking” helps

stabilize protein

structure.

Cross-linking of

cysteines in hair

proteins maintains the

curliness or straightness

of hair. Straight hair can

be “permanently” curled

by shaping it around

curlers, then breaking

and re-forming the

cross-linking bonds.

Acts as a base; can

pick up an H+ from

the surrounding

solution (water, in

living organisms).

Ionized, with a

charge of 1+, under

cellular conditions.

(nonionized)

(ionized)

Slide 34

Fig. 4-10c

STRUCTURE

EXAMPLE

NAME OF

COMPOUND

FUNCTIONAL

PROPERTIES

Carboxyl

Acetic acid, which gives vinegar its sour taste

Carboxylic acids, or organic acids

Has acidic properties

because the covalent bond between oxygen and hydrogen is so polar; for example,

Found in cells in the ionized form with a charge of 1– and called a carboxylate ion (here, specifically, the acetate ion).

Acetic acid

Acetate ion

Slide 35

Fig. 4-10d

STRUCTURE

EXAMPLE

NAME OF

COMPOUND

FUNCTIONAL

PROPERTIES

Amino

Because it also has a carboxyl group, glycine is both an amine and

a carboxylic acid; compounds with both groups are called amino acids.

Amines

Acts as a base; can pick up an H+ from the surrounding solution (water, in living organisms).

Ionized, with a charge of 1+, under cellular conditions.

(ionized)

(nonionized)

Glycine

Slide 36

Fig. 4-10e

STRUCTURE

EXAMPLE

NAME OF

COMPOUND

FUNCTIONAL