5 Steps to a 5 AP Biology, 2014-2015 Edition

of the compound, which provides an amino acid’s unique personal characteristics. For instance,

acidic amino acids have acidic R groups, basic amino acids have basic R groups, and so forth.

Many students preparing for the AP exam wonder if they need to memorize the 20 amino

acids and their structures and whether they are polar, nonpolar, or charged. This is a lot of

effort for perhaps one multiple-choice question that you might encounter on the exam. We

think that this time would be better spent studying other potential exam questions. If this is

of any comfort to you, we have yet to see an AP Biology question that asks something to the

effect of “Which of these 5 amino acids is nonpolar?” (Disclaimer:This does not mean that it

will never happen ☺.) It is more important for you to identify the general structure of an

amino acid and know the process of protein synthesis, which we discuss in Chapter 15.

A protein consists of amino acids linked together as shown in Figure 5.8. They are most

often much larger than that depicted here. Figure 5.8 is included to enable you to identify

a peptide linkage on the exam. Most proteins have many more amino acids in the chain.

The AP exam may expect you to know about the structure of proteins:

Primary structure.The order of the amino acids that make up the protein.

Secondary structure.Three-dimensional arrangement of a protein caused by hydrogen

bonding at regular intervals along the polypeptide backbone.

Tertiary structure.Three-dimensional arrangement of a protein caused by interaction

among the various R groups of the amino acids involved.

Quaternary structure.The arrangement of separate polypeptide “subunits” into a single pro-

tein. Not all proteins have quaternary structure; many consist of a single polypeptide chain.

Proteins with only primary and secondary structure are called fibrousproteins. Proteins

with only primary, secondary, and tertiary structures are called globularproteins. Either

fibrous or globular proteins may contain a quaternary structure if there is more than one

polypeptide chain.

Enzymes

Enzymesare proteins that act as organic catalysts and will be encountered often in your

review for this exam. Catalysts speed up reactions by lowering the energy (activation

energy) needed for the reaction to take place, but are not used up in the reaction. The sub-

stances that enzymes act on are known as substrates.

Enzymes are selective; they interact only with particular substrates. It is the shape of the

enzyme that provides the specificity. The part of the enzyme that interacts with the sub-

strate is called the active site.Theinduced-fit modelof enzyme-substrate interaction

Chemistry ❮ 45

Figure 5.8 Amino acid structure exhibiting peptide linkage.

R H R H

H

Peptide bonds

H OH

R

OH O

H 2 N CCNNCC C CO

CT teacher:
“The topic of
enzymes is full
of essay
material. Know
it well.”

KEY IDEA

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