M3

Question 1

Which of the following statements is correct?

Answer 1

peptide bonds are essentially planar, with no rotation about the C—N axis.

Question 2

Which of the following pairs of bonds within a peptide backbone show free rotation around both bonds?

Answer 2

Cα—C and N—Cα

Question 3

In the alpha helix the hydrogen bonds:

Answer 3

are roughly parallel to the axis of the helix.

Question 4

A naturally occurring hindrance to the formation of α helix is the presence of:

Answer 4

a Pro residue.

Question 5

Amino acid residues commonly found in the middle of beta turn are:

Answer 5

Pro and Gly.

Question 6

Experiments on denaturation and renaturation of the enzyme ribonuclease (RNase) have shown that:

Answer 6

the primary sequence of RNase is sufficient to determine its specific secondary and tertiary structure.

Question 7

Of the 20 standard amino acids, only ______ is not optically active. The reason is that its side chain _____.

Answer 7

glycine; is a hydrogen atom

Question 8

Two amino acids of the standard 20 contain sulfur atoms. They are:

Answer 8

methionine and cysteine.

Question 9

The peptide alanylglutamylglycylalanylleucine has:

Answer 9

four peptide bonds.

Question 10

By adding SDS (sodium dodecyl sulfate) during the electrophoresis of proteins, it is possible to:

Answer 10

separate proteins exclusively on the basis of molecular weight.

Question 11

To determine the isoelectric point of a protein, first establish that a gel:

Answer 11

exhibits a stable pH gradient when ampholytes become distributed in an electric field.

Question 12

Which amino acids contain aliphatic hydroxyl groups?

Answer 12

serine and threonine

Question 13

The term “proteome” has been used to describe:

Answer 13

the complement of proteins encoded by an organism’s DNA.

Question 14

Which of the following plays a role in the degradation of proteins?

Answer 14

ubiquitin, proteasome

Question 15

An allosteric interaction between a ligand and a protein is one in which:

Answer 15

binding of a molecule to a binding site affects binding properties of another site on the protein.

Question 16

Hydrophobic interactions make important energetic contributions to:

Answer 16

binding of a hormone to its receptor protein, enzyme-substrate interactions, membrane structure, three-dimensional folding of a polypeptide chain

Question 17

Misfolding of polypeptides is a serious problem in cells. Which of the following diseases are associated with an accumulation of misfolded polypeptides?

Answer 17

Alzheimer’s and Parkinson’s only

Question 18

In sickle-cell disease, as a result of a single amino acid change, the mutant hemoglobin tetramers associate with each other and assemble into large fibers. Based on this information alone, we can conclude that sickle-cell hemoglobin exhibits:

Answer 18

altered primary structure and altered quaternary structure; the secondary and tertiary structures may or may not be altered.

Question 19

What aspects of protein structure are stabilized or assisted by hydrogen bonds?

Answer 19

secondary, tertiary, and quaternary structures, but not primary structure