Essentials of Anatomy and Physiology

compounds such as proteins and carbohydrates are
complex and precise arrangements of these atoms
covalently bonded to one another. Covalent bonds are
relatively strong and are not weakened in an aqueous
solution. This is important because the proteins pro-
duced by the body, for example, must remain intact in
order to function properly in the water of our cells and
blood. The functions of organic compounds will be
considered later in this chapter.

DISULFIDE BONDS AND
HYDROGEN BONDS

Two other types of bonds that are important to
the chemistry of the body are disulfide bonds and

hydrogen bonds. Disulfide bonds are found in some

proteins. Hydrogen bonds are part of many different

molecules.

A disulfide bond(also called a disulfide bridge) is a

covalent bond formed between two atoms of sulfur,

usually within the same large protein molecule. The

hormone insulin, for example, is a protein that must

have a very specific three-dimensional shape in order

to function properly to regulate the blood glucose

level. Each molecule of insulin has two disulfide bonds

that help maintain its proper shape and function (see

Box Fig. 10–A). Other proteins with shapes that

depend upon disulfide bonds are antibodies of the

immune system (see Fig. 14–8) and keratin of the skin

and hair.

Some Basic Chemistry 27

Figure 2–3. Formation of covalent bonds. (A) Two atoms of oxygen share two electrons

each, forming a molecule of oxygen gas. (B) An atom of oxygen shares one electron with

each of two hydrogen atoms, each sharing its electron. A molecule of water is formed.

QUESTION:Which of the bonds shown here is a double covalent bond?

O + O = O 2 O=O

8+ + 8+ = 8+ 8+

A

O + H+H = H 2 O O

H H

8+ + =

1+

1+

1+ 1+

8+

B