MCAT Biochemistry Practice Test 1: Amino Acids, Peptides, and Proteins

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1. In a neutral solution, most amino acids exist as:

  • A. positively charged compounds.
  • B. zwitterions.
  • C. negatively charged compounds.
  • D. hydrophobic molecules.

2. At pH 7, the charge on a glutamic acid molecule is:

  • A. –2.
  • B. –1.
  • C. 0
  • D. 1

3. Which of the following statements is most likely to be true of nonpolar R groups in aqueous solution?

  • A. They are hydrophilic and found buried within proteins.
  • B. They are hydrophilic and found on protein surfaces.
  • C. They are hydrophobic and found buried within proteins.
  • D. They are hydrophobic and found on protein surfaces.

4. Which of these statements concerning peptide bonds is FALSE?

  • A. Their formation involves a reaction between an amino group and a carboxyl group.
  • B. They are the primary bonds that hold amino acids together.
  • C. They have partial double bond character.
  • D. Their formation involves hydration reactions.

5. How many distinct tripeptides can be formed from one valine molecule, one alanine molecule, and one leucine molecule?

  • A. 1
  • B. 3
  • C. 6
  • D. 27

6. Which of these is most likely to be preserved when a protein is denatured?

  • A. Primary structure
  • B. Secondary structure
  • C. Tertiary structure
  • D. Quaternary structure

7. An α-helix is most likely to be held together by:

  • A. disulfide bonds.
  • B. hydrophobic effects.
  • C. hydrogen bonds.
  • D. ionic attractions between side chains.

8. Which of the following is least likely to cause denaturation of proteins?

  • A. Heating the protein to 100°C
  • B. Adding 8 M urea
  • C. Moving it to a more hypotonic environment
  • D. Adding a detergent such as sodium dodecyl sulfate

9. A particular α-helix is known to cross the cell membrane. Which of these amino acids is most likely to be found in the transmembrane portion of the helix?

  • A. Glutamate
  • B. Lysine
  • C. Phenylalanine
  • D. Aspartate

10. Which of these amino acids has a chiral carbon in its side chain?

I. Serine

II. Threonine

III. Isoleucine

  • A. I only
  • B. II only
  • C. II and III only
  • D. I, II, and III

11. Adding concentrated strong base to a solution containing an enzyme often reduces enzyme activity to zero. In addition to causing protein denaturation, which of the following is another plausible reason for the loss of enzyme activity?

  • A. Enzyme activity, once lost, cannot be recovered.
  • B. The base can cleave peptide residues.
  • C. Adding a base catalyzes protein polymerization.
  • D. Adding a base tends to deprotonate amino acids on the surface of proteins.

12. Which of these amino acids has a side chain that can become ionized in cells?

  • A. Histidine
  • B. Leucine
  • C. Proline
  • D. Threonine

13. In lysine, the pKa of the side chain is about 10.5. Assuming that the pKa of the carboxyl and amino groups are 2 and 9, respectively, the pI of lysine is closest to:

  • A. 5.5.
  • B. 6.2.
  • C. 7.4.
  • D. 9.8.

14. Which of the following is a reason for conjugating proteins?

I. To direct their delivery to a particular organelle

II. To direct their delivery to the cell membrane

III. To add a cofactor needed for their activity

  • A. I only
  • B. II only
  • C. II and III only
  • D. I, II, and III

15. Collagen consists of three helices with carbon backbones that are tightly wrapped around one another in a "triple helix." Which of these amino acids is most likely to be found in the highest concentration in collagen?

  • A. Proline
  • B. Glycine
  • C. Threonine
  • D. Cysteine