MCAT Diagnostic -Biological and Biochemical
Foundations of Living Systems Exam
Questions And Correct Answers (Verified
Answers) Plus Rationales 2025/2026 Q&A
1. Which macromolecule is primarily responsible for catalyzing
biochemical reactions in the cell?
A) Carbohydrates
B) Lipids
C) Proteins
D) Nucleic acids
Rationale: Enzymes are proteins that catalyze biochemical reactions,
reducing the activation energy required.
2. The secondary structure of a protein is stabilized mainly by:
A) Disulfide bonds
B) Hydrogen bonds
C) Ionic interactions
D) Van der Waals forces
Rationale: Alpha-helices and beta-sheets are maintained by hydrogen
bonds between the backbone amide and carbonyl groups.
3. Which organelle is primarily responsible for ATP production?
A) Nucleus
B) Endoplasmic reticulum
C) Mitochondria
D) Golgi apparatus
Rationale: Mitochondria generate ATP through oxidative
phosphorylation.
4. Glycolysis occurs in the:
A) Nucleus
, B) Cytoplasm
C) Mitochondrial matrix
D) Endoplasmic reticulum
Rationale: Glycolysis is the anaerobic breakdown of glucose to
pyruvate, occurring in the cytoplasm.
5. Which molecule stores genetic information in cells?
A) Protein
B) Lipid
C) DNA
D) Carbohydrate
Rationale: DNA encodes the information required for protein
synthesis and cellular function.
6. The rate-limiting enzyme in glycolysis is:
A) Hexokinase
B) Phosphofructokinase-1 (PFK-1)
C) Pyruvate kinase
D) Lactate dehydrogenase
Rationale: PFK-1 controls the conversion of fructose-6-phosphate to
fructose-1,6-bisphosphate.
7. A mutation that changes a codon but does not alter the amino
acid sequence is called:
A) Nonsense mutation
B) Silent mutation
C) Missense mutation
D) Frameshift mutation
Rationale: Silent mutations do not affect the amino acid due to the
redundancy of the genetic code.
8. Which process involves the movement of water across a
semipermeable membrane?
A) Diffusion
, B) Osmosis
C) Active transport
D) Facilitated diffusion
Rationale: Osmosis is the passive movement of water across a
membrane from low solute concentration to high solute
concentration.
9. What is the main function of the ribosome?
A) DNA replication
B) Lipid synthesis
C) Protein synthesis
D) ATP production
Rationale: Ribosomes translate mRNA into polypeptide chains.
10. Which type of RNA carries amino acids to the ribosome?
A) mRNA
B) rRNA
C) tRNA
D) snRNA
Rationale: tRNA matches amino acids to codons on mRNA during
translation.
11. In enzyme kinetics, which statement is true about
competitive inhibitors?
A) They decrease Vmax
B) They increase Km
C) They permanently bind the enzyme
D) They do not affect Km
Rationale: Competitive inhibitors compete with the substrate for the
active site, increasing Km but not affecting Vmax.
12. Which lipid is the primary component of the cell
membrane?
A) Triglycerides
Foundations of Living Systems Exam
Questions And Correct Answers (Verified
Answers) Plus Rationales 2025/2026 Q&A
1. Which macromolecule is primarily responsible for catalyzing
biochemical reactions in the cell?
A) Carbohydrates
B) Lipids
C) Proteins
D) Nucleic acids
Rationale: Enzymes are proteins that catalyze biochemical reactions,
reducing the activation energy required.
2. The secondary structure of a protein is stabilized mainly by:
A) Disulfide bonds
B) Hydrogen bonds
C) Ionic interactions
D) Van der Waals forces
Rationale: Alpha-helices and beta-sheets are maintained by hydrogen
bonds between the backbone amide and carbonyl groups.
3. Which organelle is primarily responsible for ATP production?
A) Nucleus
B) Endoplasmic reticulum
C) Mitochondria
D) Golgi apparatus
Rationale: Mitochondria generate ATP through oxidative
phosphorylation.
4. Glycolysis occurs in the:
A) Nucleus
, B) Cytoplasm
C) Mitochondrial matrix
D) Endoplasmic reticulum
Rationale: Glycolysis is the anaerobic breakdown of glucose to
pyruvate, occurring in the cytoplasm.
5. Which molecule stores genetic information in cells?
A) Protein
B) Lipid
C) DNA
D) Carbohydrate
Rationale: DNA encodes the information required for protein
synthesis and cellular function.
6. The rate-limiting enzyme in glycolysis is:
A) Hexokinase
B) Phosphofructokinase-1 (PFK-1)
C) Pyruvate kinase
D) Lactate dehydrogenase
Rationale: PFK-1 controls the conversion of fructose-6-phosphate to
fructose-1,6-bisphosphate.
7. A mutation that changes a codon but does not alter the amino
acid sequence is called:
A) Nonsense mutation
B) Silent mutation
C) Missense mutation
D) Frameshift mutation
Rationale: Silent mutations do not affect the amino acid due to the
redundancy of the genetic code.
8. Which process involves the movement of water across a
semipermeable membrane?
A) Diffusion
, B) Osmosis
C) Active transport
D) Facilitated diffusion
Rationale: Osmosis is the passive movement of water across a
membrane from low solute concentration to high solute
concentration.
9. What is the main function of the ribosome?
A) DNA replication
B) Lipid synthesis
C) Protein synthesis
D) ATP production
Rationale: Ribosomes translate mRNA into polypeptide chains.
10. Which type of RNA carries amino acids to the ribosome?
A) mRNA
B) rRNA
C) tRNA
D) snRNA
Rationale: tRNA matches amino acids to codons on mRNA during
translation.
11. In enzyme kinetics, which statement is true about
competitive inhibitors?
A) They decrease Vmax
B) They increase Km
C) They permanently bind the enzyme
D) They do not affect Km
Rationale: Competitive inhibitors compete with the substrate for the
active site, increasing Km but not affecting Vmax.
12. Which lipid is the primary component of the cell
membrane?
A) Triglycerides
