The Foundations of Chemistry

NUCLEIC ACIDS

We have seen that polysaccharides are polymers composed of a single type of monomer

(carbohydrates), as are proteins (amino acids). The third type of biopolymer is more

complex. Nucleic acids use three very different types of monomers: the phosphate group,

one of two simple carbohydrate units (deoxyribose or ribose), and selected organic bases

(Figure 28-15). A typical segment of the resulting polymer is shown in Figure 28-16.

There are two types of nucleic acids: ribonucleic acid (RNA) and deoxyribonucleic acid

(DNA). One of the ways in which they differ is in the carbohydrate that they contain.

28-10

1134 CHAPTER 28: Organic Chemistry II: Shapes, Selected Reactions, and Biopolymers

TABLE 28-7 Some Functions of Proteins

Example Function

Enzymes

amylase converts starch to glucose

DNA polymerase I repairs DNA molecule

trans aminase transfers amino group from one amino acid to another

Structural Proteins

viral coat proteins outer covering of virus

keratin hair, nails, horns, hoofs

collagen tendons, cartilage

Hormones

insulin, glucagon regulate glucose metabolism

oxytocin regulates milk production in female mammals

vasopressin increases retention of water by kidney

Contractile Proteins

actin thin contractile filaments in muscle

myosin thick filaments in muscle

Storage Proteins

casein a nutrient protein in milk

ferritin stores iron in spleen and egg yolk

Transport Proteins

hemoglobin carries O 2 in blood

myoglobin carries O 2 in muscle

serum albumin carries fatty acids in blood

cytochrome c transfers electrons

Immunological Proteins

-globulins form complexes with foreign proteins

Toxins

neurotoxin blocker of nerve function in cobra venom

ricin nerve toxin in South American frog (most toxic substance

known—0.000005 g is fatal to humans)