Green Chemistry and the Ten Commandments

Chap. 5. The Wonderful World of Carbon: Organic Chemistry and Biochemicals 129

several levels of protein structure. The first of these is determined by the order of amino
acids in the protein macromolecule. Folding of protein molecules and pairing of two
different protein molecules further determine structure. The loss of protein structure,
called denaturation, can be very damaging to proteins and to the organism in which
they are contained.

C OH

O

C

H

H

H 2 N

Glycine                                                                                                                                 Cysteine                                                                                                                                Tyrosine

C OH

O

C

H

H 2 N

SH

H C H

C OH

O

C

H

H 2 N

OH

H C H

C

O

C

H

N

OH

H C H

H

C

O

C

H

H

N

H C H

SH

N

H

C

O

C

H H

Figure 5.8. Three amino acids. Glycine is the simplest amino acid. All others have the basic glycine
structure except that different groups are substituted for the H designated in glycine by an arrow. The
lower structure shows these three amino acids linked together in a macromolecule chain composing a
protein. For each linkage, one molecule of H 2 O is lost. The peptide linkages holding amino acids together
in proteins is outlined by a dashed rectangle.

Two major kinds of proteins are tough fibrous proteins that compose hair, tendons,
muscles, feathers, and silk, and spherical or oblong-shaped globular proteins, such
as hemoglobin in blood or the proteins that comprise enzymes. Proteins serve many
functions. These include nutrient proteins, such as casein in milk, structural proteins,
such as collagen in tendons, contractile proteins, such as those in muscle, and regulatory

proteins, such as insulin, that regulate biochemical processes.

5.9. Lipids: Fats, Oils, and Hormones

Lipids differ from most other kinds of biomolecules in that they are repelled by
water. Lipids can be extracted from biological matter by organic solvents, such as
diethyl ether or toluene. Recall that proteins and carbohydrates are distinguished largely
by chemically similar characteristics and structures. However, lipids have a variety of
chemical structures that share the common physical characteristic of solubility in organic
solvents. Many of the commonly encountered lipid fats and oils are esters of glycerol
alcohol, CH 2 (OH)CH(OH)CH 2 (OH), and long-chain carboxylic acids (fatty acids), such