Title: MCAT Original Practice-2 - 80 MCQ Cards / Biological and Biochemical Foundations of Living Systems
Tags: biological mcat practice2

Question: In the enzyme assay, drug X lowers the plateau and shifts the curve right. Which interpretation is most consistent?
Explanation: Correct: B. A lower apparent Vmax plus altered apparent Km is consistent with mixed inhibition.
Difficulty: Hard
Other fields (not shown on cards):
Choices: Pure competitive inhibition
Mixed inhibition
No inhibition
Increased enzyme concentration
Correct: B

Question: On the gel, lane C shows more bands than lanes A or B. What is the most reasonable conclusion?
Explanation: Correct: A. More bands indicate more fragment sizes detected under the gel conditions.
Difficulty: Easy
Other fields (not shown on cards):
Choices: Sample C contains more distinct DNA fragments
Sample C has the smallest total mass only
Lane C failed to load
All lanes contain identical fragments
Correct: A

Question: The amino acid side chain shown is most consistent with which amino acid?
Explanation: Correct: A. A CH2-OH side chain identifies serine, a polar uncharged amino acid.
Difficulty: Easy
Other fields (not shown on cards):
Choices: Serine
Valine
Lysine
Phenylalanine
Correct: A

Question: Which step in the metabolic flow diagram produces CO2 as pyruvate is converted before the citric acid cycle?
Explanation: Correct: B. Pyruvate dehydrogenase converts pyruvate to acetyl-CoA and releases CO2.
Difficulty: Medium
Other fields (not shown on cards):
Choices: Glucose to glucose-6-phosphate
Pyruvate to acetyl-CoA
Citrate to glucose
ATP to ADP
Correct: B

Question: A mutation removes the nuclear localization signal from a transcription factor. Where is the protein most likely to accumulate?
Explanation: Correct: B. Without a nuclear localization signal, import into the nucleus is impaired, so cytosolic accumulation is likely.
Difficulty: Medium
Other fields (not shown on cards):
Choices: Nucleus
Cytosol
Mitochondrial matrix
Lysosome
Correct: B

Question: During DNA replication, which enzyme relieves supercoiling ahead of the replication fork?
Explanation: Correct: B. Topoisomerases cut and reseal DNA to relieve torsional strain.
Difficulty: Easy
Other fields (not shown on cards):
Choices: DNA ligase
Topoisomerase
Primase
Telomerase
Correct: B

Question: A cell treated with a microtubule depolymerizing drug is most directly impaired in which process?
Explanation: Correct: A. Mitotic spindle fibers are microtubule-based and are required for chromosome segregation.
Difficulty: Medium
Other fields (not shown on cards):
Choices: Chromosome separation during mitosis
Peptide bond formation
Glycolysis
mRNA splicing
Correct: A

Question: A protein is found in the extracellular matrix and contains repeated Gly-X-Y motifs. Which protein is most likely?
Explanation: Correct: A. Collagen has a characteristic Gly-X-Y repeat that supports triple-helix formation.
Difficulty: Medium
Other fields (not shown on cards):
Choices: Collagen
Hemoglobin
Actin
Insulin
Correct: A

Question: A patient has low blood calcium. Which hormone would normally increase to help restore calcium levels?
Explanation: Correct: B. PTH raises blood calcium by effects on bone, kidney, and vitamin D activation.
Difficulty: Easy
Other fields (not shown on cards):
Choices: Insulin
Parathyroid hormone
Aldosterone
Melatonin
Correct: B

Question: In the pedigree, affected children appear from unaffected parents and both sexes can be affected. Which inheritance pattern is most likely?
Explanation: Correct: A. Unaffected parents having affected sons and daughters is most consistent with autosomal recessive inheritance.
Difficulty: Medium
Other fields (not shown on cards):
Choices: Autosomal recessive
Y-linked
Mitochondrial
X-linked dominant with full penetrance
Correct: A

Question: A frameshift mutation occurs early in the coding sequence. Why is it often more damaging than a silent mutation?
Explanation: Correct: A. Frameshifts alter codon grouping downstream and often introduce premature stop codons.
Difficulty: Easy
Other fields (not shown on cards):
Choices: It changes the reading frame for downstream codons
It affects only introns
It preserves every amino acid
It only changes DNA methylation
Correct: A

Question: Which organelle is most directly responsible for adding mannose-6-phosphate tags to lysosomal enzymes?
Explanation: Correct: A. Lysosomal enzyme sorting tags are generated in the Golgi apparatus.
Difficulty: Medium
Other fields (not shown on cards):
Choices: Golgi apparatus
Peroxisome
Smooth ER
Nucleus
Correct: A

Question: An action potential trace crosses threshold and rapidly rises. Which ion movement primarily causes the rising phase?
Explanation: Correct: A. Voltage-gated sodium channels open, allowing Na+ influx and depolarization.
Difficulty: Medium
Other fields (not shown on cards):
Choices: Na+ influx
K+ influx
Cl− efflux
Ca2+ efflux from the cell
Correct: A

Question: A molecule blocks the electron transport chain at Complex IV. Which immediate effect is expected?
Explanation: Correct: A. Complex IV transfers electrons to oxygen; blocking it reduces oxygen consumption and backs up electron flow.
Difficulty: Hard
Other fields (not shown on cards):
Choices: Oxygen consumption decreases
Glycolysis stops instantly
ATP synthase pumps protons out
NADH oxidation increases
Correct: A

Question: Which RNA polymerase product in eukaryotes is most directly processed by splicing?
Explanation: Correct: A. Eukaryotic pre-mRNA contains introns removed by the spliceosome.
Difficulty: Easy
Other fields (not shown on cards):
Choices: Pre-mRNA
Mature tRNA only
rRNA only
DNA primer
Correct: A

Question: A competitive inhibitor is added to an enzyme reaction. On a Lineweaver-Burk plot, which change is expected for pure competitive inhibition?
Explanation: Correct: A. Competitive inhibition increases apparent Km without changing Vmax, so the y-intercept (1/Vmax) is unchanged.
Difficulty: Hard
Other fields (not shown on cards):
Choices: Same y-intercept, steeper slope
Lower y-intercept, same slope
Both lines become horizontal
x-intercept unchanged
Correct: A

Question: Which immune cell type is most directly responsible for producing antibodies after activation and differentiation?
Explanation: Correct: A. Activated B cells can differentiate into plasma cells that secrete antibodies.
Difficulty: Easy
Other fields (not shown on cards):
Choices: Plasma cell
Neutrophil
Cytotoxic T cell
Eosinophil
Correct: A

Question: A membrane becomes more permeable to potassium at rest. What happens to membrane potential?
Explanation: Correct: A. Increased K+ permeability drives Vm toward the potassium equilibrium potential, usually hyperpolarizing the cell.
Difficulty: Hard
Other fields (not shown on cards):
Choices: It moves closer to EK and becomes more negative
It becomes more positive immediately
It becomes exactly zero
It no longer depends on ions
Correct: A

Question: Which molecule directly carries amino acids to the ribosome during translation?
Explanation: Correct: A. Transfer RNA molecules carry specific amino acids and match codons via anticodons.
Difficulty: Easy
Other fields (not shown on cards):
Choices: tRNA
mRNA
rRNA
snRNA
Correct: A

Question: A researcher knocks out a kinase that normally phosphorylates glycogen phosphorylase. What metabolic result is most likely?
Explanation: Correct: A. Phosphorylation activates glycogen phosphorylase in glycogenolysis; blocking the kinase reduces breakdown.
Difficulty: Medium
Other fields (not shown on cards):
Choices: Reduced glycogen breakdown
Increased DNA replication
Blocked urea excretion only
Increased protein translation at all ribosomes
Correct: A