ACS Biochemistry Final Exam Review Bundle – Full-Length Practice Test 1 (Questions 1-50): Complete Questions, Answers & Rationales for ACS Biochemistry Exam Success | 2026/2027 Edition

ACS BIOCHEMISTRY FINAL EXAM
REVIEW BUNDLE
Full-Length Practice Test 1 (Questions 1-50)
Foundations: Amino Acids, Proteins, and Enzymes
1. Which amino acid has a side chain that can form covalent disulfide bonds?
 A) Methionine
 B) Cysteine
 C) Serine
 D) Tyrosine
Answer: B) Cysteine
Rationale: Cysteine contains a thiol (-SH) group that can oxidize to form a
disulfide bond (-S-S-) with another cysteine residue. Methionine contains
sulfur but in a thioether form, which cannot form disulfides.
2. At pH 7.0, which amino acid carries a net positive charge?
 A) Aspartate
 B) Glutamate
 C) Lysine
 D) Histidine
Answer: C) Lysine
Rationale: Lysine has a pKa of approximately 10.5 for its side chain amino
group. At pH 7.0, it is protonated and positively charged. Aspartate and
Glutamate are negatively charged; Histidine is mostly neutral at pH 7.0
(pKa ~6.0).
3. The secondary structure of a protein is defined by:
 A) The sequence of amino acids

,  B) The three-dimensional arrangement of all atoms
 C) The local folding patterns like alpha-helices and beta-sheets
 D) The association of multiple polypeptide chains
Answer: C) The local folding patterns like alpha-helices and beta-sheets
Rationale: Secondary structure refers to the local, repetitive folding of the
polypeptide backbone stabilized by hydrogen bonds. Primary structure is the
sequence; tertiary is the overall 3D shape; quaternary is the association of
subunits.
4. Which type of inhibition can be overcome by increasing substrate
concentration?
 A) Competitive
 B) Non-competitive
 C) Uncompetitive
 D) Irreversible
Answer: A) Competitive
Rationale: Competitive inhibitors bind to the active site, directly competing
with the substrate. Increasing substrate concentration increases the
probability of substrate binding, thus overcoming the inhibition. Vmax
remains unchanged, but Km increases.
5. The Michaelis constant (Km) is a measure of:
 A) The maximum velocity of the reaction
 B) The affinity of the enzyme for the substrate
 C) The turnover number of the enzyme
 D) The pH optimum of the enzyme
Answer: B) The affinity of the enzyme for the substrate
Rationale: Km is the substrate concentration at which the reaction velocity
is half of Vmax. It is inversely related to the enzyme's affinity for the
substrate (lower Km = higher affinity).

,6. An enzyme that catalyzes the transfer of a phosphate group from ATP to a
substrate is called a:
 A) Phosphatase
 B) Kinase
 C) Phosphorylase
 D) Dehydrogenase
Answer: B) Kinase
Rationale: Kinases transfer phosphate groups from high-energy compounds
(like ATP) to specific substrates. Phosphatases remove phosphate groups.
Phosphorylases add phosphate groups from inorganic phosphate.
7. The pKa of a buffer is 6.8. At pH 8.8, the ratio of [A-]/[HA] is closest to:
 A) 1:100
 B) 1:10
 C) 100:1
 D) 10:1
Answer: C) 100:1
Rationale: Using the Henderson-Hasselbalch equation: pH = pKa + log([A-
]/[HA]) => 8.8 = 6.8 + log([A-]/[HA]) => log([A-]/[HA]) = 2.0 => [A-
]/[HA] = 100:1.
8. Which of the following best describes the "induced fit" model of enzyme
catalysis?
 A) The enzyme is rigid and the substrate must fit exactly into the active site.
 B) The enzyme undergoes a conformational change upon substrate binding.
 C) The active site is permanently shaped to fit the substrate.
 D) The enzyme changes the substrate's conformation.
Answer: B) The enzyme undergoes a conformational change upon
substrate binding.
Rationale: The induced fit model proposes that the enzyme's active site is not

, a perfect fit for the substrate initially. Upon binding, the enzyme changes
k. k. k. k. k. k. k. k. k. k. k.




shape to accommodate and stabilize the transition state.
k. k. k. k. k. k. k. k.




9. In a Lineweaver-Burk plot, the y-intercept represents:
k. k. k. k. k. k.




 A) -1/Km k.




 B) 1/Vmaxk.




 C) Km/Vmax
k.




 D) Vmax k.




Answer: B) 1/Vmax k. k.




Rationale: The Lineweaver-Burk plot is a double reciprocal plot (1/V vs
k. k. k. k. k. k. k. k. k. k.




1/[S]). The y-intercept is 1/Vmax, and the x-intercept is -1/Km.
k. k. k. k. k. k. k. k. k. k.




10. The quaternary structure of hemoglobin is stabilized by:
k. k. k. k. k. k. k.




 A) Peptide bonds
k. k.




 B) Disulfide bonds only
k. k. k.




 C) Hydrophobic interactions and hydrogen bonds
k. k. k. k. k.




 D) Covalent bonds only
k. k. k.




Answer: C) Hydrophobic interactions and hydrogen bonds
k. k. k. k. k. k.




Rationale: Quaternary structure refers to the interactions between multiple
k. k. k. k. k. k. k. k.




polypeptide subunits. These are typically stabilized by non-covalent
k. k. k. k. k. k. k. k.




interactions like hydrophobic interactions, hydrogen bonds, and ionic
k. k. k. k. k. k. k. k.




interactions.
k.




11. Which amino acid is most likely found in the interior of a globular
k. k. k. k. k. k. k. k. k. k. k. k.




protein?
k.




 A) Lysine k.




 B) Arginine
k.




 C) Leucine
k.




 D) Serine k.




Answer: C) Leucine k. k.




Rationale: Leucine is a nonpolar, hydrophobic amino acid. It is typically
k. k. k. k. k. k. k. k. k. k.