MCAT (Biological and Biochemical) 2 — Questions and Answers
Question 1: Which enzyme catalyzes the committed step of glycolysis?
- Hexokinase
- Phosphofructokinase-1 (Correct answer)
- Pyruvate kinase
- Phosphoglucose isomerase
Correct answer: Phosphofructokinase-1
Phosphofructokinase-1 (PFK-1) catalyzes the irreversible conversion of fructose-6-phosphate to fructose-1,6-bisphosphate, which is the committed and rate-limiting step of glycolysis.
Question 2: During oxidative phosphorylation, where do electrons from NADH ultimately transfer?
- Carbon dioxide
- Molecular oxygen (Correct answer)
- NAD+
- ATP
Correct answer: Molecular oxygen
Electrons from NADH pass through the electron transport chain and are ultimately accepted by molecular oxygen (O2), which is reduced to water (H2O).
Question 3: Which type of RNA carries the genetic code from the nucleus to the ribosome for translation?
- tRNA
- rRNA
- mRNA (Correct answer)
- snRNA
Correct answer: mRNA
Messenger RNA (mRNA) carries the genetic information transcribed from DNA and serves as the template for protein synthesis at the ribosome.
Question 4: A mutation that converts a codon from UAU (Tyr) to UAA results in what type of mutation?
- Missense mutation
- Silent mutation
- Nonsense mutation (Correct answer)
- Frameshift mutation
Correct answer: Nonsense mutation
UAA is a stop codon; converting an amino acid codon to a stop codon creates a nonsense mutation that causes premature termination of translation.
Question 5: Which bond connects amino acids in a polypeptide chain?
- Hydrogen bond
- Disulfide bond
- Peptide bond (Correct answer)
- Ionic bond
Correct answer: Peptide bond
A peptide bond is a covalent amide bond formed between the carboxyl group of one amino acid and the amino group of the next during translation.
Question 6: Which organelle is responsible for modifying, sorting, and packaging proteins for secretion?
- Rough endoplasmic reticulum
- Golgi apparatus (Correct answer)
- Lysosome
- Mitochondria
Correct answer: Golgi apparatus
The Golgi apparatus receives proteins from the ER, modifies them (e.g., glycosylation), and sorts them into vesicles destined for the cell membrane, lysosomes, or secretion.
Question 7: In the citric acid cycle, how many NADH molecules are produced per acetyl-CoA?
- 1
- 2
- 3 (Correct answer)
- 4
Correct answer: 3
Each turn of the citric acid cycle produces 3 NADH molecules (at the isocitrate dehydrogenase, α-ketoglutarate dehydrogenase, and malate dehydrogenase steps).
MCAT (Biological and Biochemical) 2
Which enzyme catalyzes the committed step of glycolysis?