Biochemistry 501 Unit 1

What is the maximum number of hydrogen bonds that water may form?

4

The strongest hydrogen bonds have angles of ________.

180°

The spontaneous clustering of lipids is driven by an energetically favorable increase in the _______ of water.

Entropy

Phosphoric acid has a pKa of 2.1. At what pH will 75% of phosphoric acid be in the conjugate base form?

2.6

All of the amino acids are chiral except:

Glycine

Which amino acids are negatively charged at neutral pH?

Glutamate, aspartate

Which of the following statements regarding amino acid chemistry is CORRECT?

The pKa values of most carboxylic acid groups are above 2. At pH 7, the majority of the carboxylic acid groups will have a negative charge. The pKa values of most amino groups are above 9. At pH 7, the majority of the amino groups will have a +1 charge.

How many ionizable groups are in the following peptide? (Leucine-Valine-Aspartate-Tryptophan-Lysine)

4

Which of the following techniques separates proteins based on size?

Size exclusion chromatography

Which of the following is generally used for protein analysis but not protein purification?

SDS-PAGE

Which of the following amino acids absorbs UV light?

Tryptophan

Which of the following techniques is used to sequence a protein?

Edman degradation

Which of the following bonds in a protein does not rotate?

Peptide

How many hydrogen bonds will be found within an alpha helix that is 18 amino acids long?

14

Beta Sheets are flat.

False

Which of the following contributes the most to protein stability?

Hydrophobic effect

Myoglobin does not have a quaternary structure.

True

Which of the following is stabilized by oxygen binding?

R state hemoglobin

What amino acid(s) in hemoglobin is/are carbamylated at low pH?

The first amino acid of each subunit

The oxygen-binding curve for hemoglobin in the absence of BPG is sigmoidal.

False

Which of the following statements best describes KM?

It is the concentration of substrate required to achieve 1/2Vmax.

Which of the rate constants can be ignored at the initial stages of the reaction given below, when substrate is in large excess over the amount of product formed?

k-2 which was the second step

Which of the following statements regarding enzymes is CORRECT?

Some enzymes require cofactors; Enzymes have evolved to bind most; tightly to the transition state; Some enzymes are comprised of RNA instead of protein; Enzymes may increase the rate of reaction by 105-1017 fold.

Which of the following terms is the best measure of catalytic efficiency?

Kcat/KM

Which of the following located in the active site of the enzyme chymotrypsin participates in covalent catalysis?

The side chain of oxygen of serine

Which of the following located in the active site of the enzyme chymotrypsin participates in acid-base chemistry?

Histidine

Which of the following stabilizes the transition state oxyanion that forms during chymotrypsin catalysis?

Hydrogen bonds from N-H groups

A series of enzymes perform a multiple-step reaction pathway to produce the nucleotide cytidine triphosphate (CTP). CTP allosterically inhibits the first enzyme in the pathway. This is an example of:

Feedback inhibition

Competitive inhibitors bind to the active site of an enzyme.

True

Uncompetitive inhibitors bind to the active site of an enzyme.

False

Which of these plots represents a competitive inhibitor?

The one where they all have the same Vmax.

Which of the following statements regarding enzyme inhibitors is CORRECT?

Enzymes can still achieve Vmax in the presence of a competitive inhibitor. Vmax decrease in the presence of an uncompetitive inhibitor. KM decreases in the presence of an uncompetitive inhibitor. Both Vmax and KM change in the presence of a mixed inhibitor.

Steroids are derived from arachidonic acid.

False

Vitamin D is derived from cholesterol.

True

The percentage of the glycerophospholipid phosphatidylserine is the same in the inner layer of the phospholipid bilayer as in the outer layer of the phospholipid bilayer.

False

Which of the following statements is CORRECT of E.coli?

An E. coli cell grown at 30 degrees will have a lower percentage of unsaturated fatty acids in its membrane than one grown at 20 degrees C.