BIO 171 PRACTICE EXAM 2026/2027
QUESTIONS AND ANSWERS
1. In a Lineweaver-Burk plot, how does the presence of a competitive inhibitor affect the
graph compared to an uninhibited reaction?
A. The y-intercept increases, while the x-intercept remains the same.
B. The x-intercept shifts closer to zero, while the y-intercept remains the same.
C. Both the x-intercept and y-intercept shift away from zero.
D. The slope remains the same, but the line shifts upward.
Answer: B
Conceptual Explanation: Competitive inhibitors increase the apparent Km (shifting the x-
intercept -1/Km closer to zero) but do not change the Vmax (y-intercept 1/Vmax remains
constant).
2. What is the primary role of cholesterol in animal cell membranes at high temperatures?
A. To increase membrane fluidity by preventing fatty acid packing.
B. To act as a precursor for glycolipid synthesis.
C. To facilitate the transport of ions across the lipid bilayer.
D. To stabilize the membrane by reducing phospholipid movement.
,Answer: D
Conceptual Explanation: At high temperatures, cholesterol restricts the movement of
phospholipids, thereby reducing fluidity and maintaining membrane integrity.
3. During the light-dependent reactions of photosynthesis, what is the immediate source of
electrons that replenish the oxidized P680 chlorophyll molecules?
A. Water (H2O)
B. Photosystem I
C. NADPH
D. Carbon dioxide (CO2)
Answer: A
Conceptual Explanation: Photolysis of water splits H2O into oxygen, protons, and
electrons; these electrons replace those lost by P680 in Photosystem II.
4. Which of the following best describes the function of the Signal Recognition Particle (SRP)
during protein synthesis?
A. It catalyzes the formation of peptide bonds in the ribosome.
B. It binds to the signal peptide and halts translation until the ribosome reaches the ER.
C. It assists in the folding of proteins within the cytoplasm.
D. It degrades misfolded proteins in the proteasome.
Answer: B
, Conceptual Explanation: The SRP recognizes the N-terminal signal sequence of a nascent
polypeptide, pausing translation to facilitate docking to the Rough ER membrane.
5. In the lac operon, what occurs when lactose is present and glucose levels are low?
A. The repressor is inactive, and cAMP binds to CAP to stimulate transcription.
B. The repressor is inactive, and cAMP levels are low.
C. The repressor is bound to the operator, and CAP is inactive.
D. The RNA polymerase is blocked by the presence of allolactose.
Answer: A
Conceptual Explanation: Lactose (as allolactose) inactivates the repressor. Low glucose
increases cAMP, which activates CAP, leading to high levels of transcription.
6. A DNA template strand reads 3’-TAC GGC ATG-5’. What is the corresponding mRNA
sequence produced during transcription?
A. 5’-AUG CCG UAC-3’
B. 5’-ATG CCG TAC-3’
C. 3’-AUG CCG UAC-5’
D. 5’-UAC GGC AUG-3’
Answer: A
Conceptual Explanation: mRNA is synthesized 5’ to 3’ complementary to the 3’ to 5’ DNA
template, replacing Thymine with Uracil.
QUESTIONS AND ANSWERS
1. In a Lineweaver-Burk plot, how does the presence of a competitive inhibitor affect the
graph compared to an uninhibited reaction?
A. The y-intercept increases, while the x-intercept remains the same.
B. The x-intercept shifts closer to zero, while the y-intercept remains the same.
C. Both the x-intercept and y-intercept shift away from zero.
D. The slope remains the same, but the line shifts upward.
Answer: B
Conceptual Explanation: Competitive inhibitors increase the apparent Km (shifting the x-
intercept -1/Km closer to zero) but do not change the Vmax (y-intercept 1/Vmax remains
constant).
2. What is the primary role of cholesterol in animal cell membranes at high temperatures?
A. To increase membrane fluidity by preventing fatty acid packing.
B. To act as a precursor for glycolipid synthesis.
C. To facilitate the transport of ions across the lipid bilayer.
D. To stabilize the membrane by reducing phospholipid movement.
,Answer: D
Conceptual Explanation: At high temperatures, cholesterol restricts the movement of
phospholipids, thereby reducing fluidity and maintaining membrane integrity.
3. During the light-dependent reactions of photosynthesis, what is the immediate source of
electrons that replenish the oxidized P680 chlorophyll molecules?
A. Water (H2O)
B. Photosystem I
C. NADPH
D. Carbon dioxide (CO2)
Answer: A
Conceptual Explanation: Photolysis of water splits H2O into oxygen, protons, and
electrons; these electrons replace those lost by P680 in Photosystem II.
4. Which of the following best describes the function of the Signal Recognition Particle (SRP)
during protein synthesis?
A. It catalyzes the formation of peptide bonds in the ribosome.
B. It binds to the signal peptide and halts translation until the ribosome reaches the ER.
C. It assists in the folding of proteins within the cytoplasm.
D. It degrades misfolded proteins in the proteasome.
Answer: B
, Conceptual Explanation: The SRP recognizes the N-terminal signal sequence of a nascent
polypeptide, pausing translation to facilitate docking to the Rough ER membrane.
5. In the lac operon, what occurs when lactose is present and glucose levels are low?
A. The repressor is inactive, and cAMP binds to CAP to stimulate transcription.
B. The repressor is inactive, and cAMP levels are low.
C. The repressor is bound to the operator, and CAP is inactive.
D. The RNA polymerase is blocked by the presence of allolactose.
Answer: A
Conceptual Explanation: Lactose (as allolactose) inactivates the repressor. Low glucose
increases cAMP, which activates CAP, leading to high levels of transcription.
6. A DNA template strand reads 3’-TAC GGC ATG-5’. What is the corresponding mRNA
sequence produced during transcription?
A. 5’-AUG CCG UAC-3’
B. 5’-ATG CCG TAC-3’
C. 3’-AUG CCG UAC-5’
D. 5’-UAC GGC AUG-3’
Answer: A
Conceptual Explanation: mRNA is synthesized 5’ to 3’ complementary to the 3’ to 5’ DNA
template, replacing Thymine with Uracil.
