Lipids, Carbohydrates, and Proteins for AP Biology (page 2)

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By — McGraw-Hill Professional
Updated on Oct 24, 2011


A protein is a compound composed of chains of amino acids. Proteins have many functions in the body—they serve as structural components, transport aids, enzymes, and cell signals, to name only a few. You should be able to identify a protein or an amino acid by sight if asked to do so on the test.

An amino acid consists of a carbon center surrounded by an amino group, a carboxyl group, a hydrogen, and an R group (See Figure 5.7.) Remember that the R stands for "rest" 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.

Lipids, Carbohydrates, and Proteins

Lipids, Carbohydrates, and Proteins

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. I think that this time would be better spent studying other potential exam questions. If this is of any comfort to you, I 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.

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

Proteins with only primary and secondary structure are called fibrous proteins. Proteins with only primary, secondary, and tertiary structures are called globular proteins. Either fibrous or globular proteins may contain a quaternary structure if there is more than one polypeptide chain.


Practice problems for these concepts can be found at:  Chemistry Review Questions for AP Biology

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