MCAT Biology 2 — Questions and Answers
Question 1: Which enzyme is responsible for removing RNA primers during DNA replication in eukaryotes?
- DNA polymerase I
- DNA polymerase δ
- RNase H combined with FEN1 (Correct answer)
- Primase
Correct answer: RNase H combined with FEN1
In eukaryotes, RNase H and FEN1 (flap endonuclease 1) work together to remove RNA primers, after which DNA polymerase δ fills the gap.
Question 2: A cell in G2 phase is treated with a drug that prevents microtubule polymerization. At which checkpoint will cell cycle arrest most likely occur?
- G1/S checkpoint
- Intra-S checkpoint
- G2/M checkpoint (Correct answer)
- Spindle assembly checkpoint
Correct answer: G2/M checkpoint
The G2/M checkpoint monitors whether DNA replication is complete and cellular machinery (including microtubules for the spindle) is ready before mitosis begins.
Question 3: Which type of RNA processing is unique to eukaryotes and involves joining of non-contiguous sequences?
- 5' capping
- Polyadenylation
- RNA splicing (Correct answer)
- Base modification
Correct answer: RNA splicing
RNA splicing removes introns and joins exons, creating a mature mRNA from non-contiguous coding sequences—a process absent in prokaryotes.
Question 4: During which stage of cellular respiration is the most ATP produced per molecule of glucose?
- Glycolysis
- Pyruvate decarboxylation
- Citric acid cycle
- Oxidative phosphorylation (Correct answer)
Correct answer: Oxidative phosphorylation
Oxidative phosphorylation generates approximately 32-34 ATP via chemiosmosis driven by the electron transport chain, far exceeding all other stages.
Question 5: A mutation in which of the following would most directly impair the ability of a eukaryotic cell to target proteins to the endoplasmic reticulum?
- Signal recognition particle (SRP) (Correct answer)
- Clathrin
- COPI coat proteins
- Dynein
Correct answer: Signal recognition particle (SRP)
The signal recognition particle recognizes the signal sequence on nascent polypeptides and directs ribosomes to the ER membrane for cotranslational translocation.
Question 6: Which of the following correctly describes the Hardy-Weinberg principle?
- Allele frequencies change predictably with each generation
- In a large random-mating population without evolutionary forces, allele frequencies remain constant (Correct answer)
- Natural selection always drives populations toward Hardy-Weinberg equilibrium
- Genetic drift is negligible only in small populations
Correct answer: In a large random-mating population without evolutionary forces, allele frequencies remain constant
Hardy-Weinberg states that in an idealized population (large, random mating, no mutation/migration/selection/drift), allele and genotype frequencies remain constant across generations.
Question 7: A protein has a Km of 2 mM and a Vmax of 100 μmol/min. At a substrate concentration of 2 mM, what is the reaction velocity?
- 25 μmol/min
- 50 μmol/min (Correct answer)
- 75 μmol/min
- 100 μmol/min
Correct answer: 50 μmol/min
By the Michaelis-Menten equation, v = Vmax[S]/(Km+[S]) = 100×2/(2+2) = 50 μmol/min; at [S]=Km, velocity is always Vmax/2.
MCAT Biology 2
Which enzyme is responsible for removing RNA primers during DNA replication in eukaryotes?