18. Amino Acids and Proteins

Give an example of a protein containing primarily alpha-helices. Is this a fibrous or globular protein?

Globular proteins are water-soluble, whereas fibrous proteins are insoluble in water. Indicate whether you expect the following amino acids to be on the surface of a globular protein or on the surface of a fibrous protein.

a. Ala

What is meant by the following terms as they apply to protein structure, and what bonds or molecular interactions stabilize that level of structure?

b. Secondary structure

Complete the following two sentences with either globular or fibrous:

a. Proteins with secondary structure composed primarily of alpha-helix are___________ proteins.

How many hydrogen bonding pairs are possible when the following two peptides interact?

Which of the following statements is true in regard to the peptide strand shown?

Examine the α-helix in Figure 18.1 and determine how many backbone C and N atoms are included in the loop between an amide hydrogen atom and the carbonyl oxygen to which it is hydrogen bonded.

Consult the β-sheet in Figure 18.2 and (a) name the bonding responsible for the sheet formation and (b) identify the specific atoms responsible for this bonding.

Draw the hexapeptide Asp-Gly-Phe-Leu-Glu-Ala in linear form showing all of the atoms, and show (using dotted lines) the hydrogen bonding that stabilizes this structure if it is part of an α-helix.

Compare and contrast the characteristics of fibrous and globular proteins. Consider biological function, water solubility, amino acid composition, secondary structure, and tertiary structure. Give examples of three fibrous and three globular proteins. (Hint: Make a table.)

Bradykinin, a peptide that helps to regulate blood pressure, has the primary structure Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg.

b. Bradykinin has a very kinked secondary structure. Why?

What happens when a primary structure forms a secondary structure?

What is the difference in hydrogen bonding between an α helix and a β−pleated sheet?

What are some differences between each of the following pairs? (16.1, 16.2, 16.3)

b. an α helix and collagen

Name the stabilizing attractive force found in secondary structures of proteins.

Describe the differences in the shape of an α helix and a β-pleated sheet.

For each of the following proteins, note whether the main secondary structure feature is α helix, β-pleated sheet, or both.

a. collagen

For each of the following proteins, note whether the main secondary structure feature is α helix, β-pleated sheet, or both.

c. hemoglobin

For each of the following proteins, note whether the main secondary structure feature is α helix, β-pleated sheet, or both.

e. hexokinase