CPC CPC Biochemistry & Biological Chemistry 2 — Questions and Answers
Question 1: Competitive inhibition of an enzyme is characterized by:
- Decreased Vmax and unchanged Km
- Unchanged Vmax and increased apparent Km (Correct answer)
- Decreased Vmax and decreased Km
- Unchanged Km and unchanged Vmax
Correct answer: Unchanged Vmax and increased apparent Km
Competitive inhibitors bind at the active site, competing with substrate; high [S] can overcome inhibition, so Vmax is unchanged, but apparent Km increases (lower apparent affinity).
Question 2: Which reaction is catalyzed by DNA polymerase during DNA replication?
- Unwinding the double helix
- Adding nucleotides to the 3'-OH end of a growing strand (Correct answer)
- Removing RNA primers
- Ligating Okazaki fragments
Correct answer: Adding nucleotides to the 3'-OH end of a growing strand
DNA polymerase catalyzes the addition of dNTPs to the free 3'-OH of the growing chain, reading the template 3'→5' and synthesizing 5'→3' with high fidelity.
Question 3: In the context of biochemistry, the term 'reducing sugar' refers to a sugar that:
- Reduces its own molecular weight during metabolism
- Contains a free anomeric hydroxyl group capable of acting as a reducing agent (Correct answer)
- Can only be metabolized under anaerobic conditions
- Has fewer than 6 carbons
Correct answer: Contains a free anomeric hydroxyl group capable of acting as a reducing agent
Reducing sugars have a free anomeric -OH group that can open to the aldehyde or keto form, allowing them to reduce oxidizing agents (e.g., Benedict's reagent, Fehling's solution).
Question 4: Which process describes the flow of genetic information according to the central dogma of molecular biology?
- Protein → RNA → DNA
- DNA → RNA → Protein (Correct answer)
- RNA → DNA → Protein
- Protein → DNA → RNA
Correct answer: DNA → RNA → Protein
The central dogma states that genetic information flows from DNA (replication) → RNA (transcription) → Protein (translation), with reverse transcription as a special exception.
Question 5: Beta-oxidation of fatty acids occurs in which cellular location and produces which primary products?
- Cytoplasm; glucose and CO2
- Mitochondrial matrix; acetyl-CoA, NADH, and FADH2 (Correct answer)
- Peroxisomes only; formate and H2O2
- Endoplasmic reticulum; fatty aldehydes
Correct answer: Mitochondrial matrix; acetyl-CoA, NADH, and FADH2
Beta-oxidation in the mitochondrial matrix (and peroxisomes for very long-chain fatty acids) sequentially cleaves two-carbon units as acetyl-CoA while generating NADH and FADH2 for ATP production.
Question 6: Which of the following amino acids contains a sulfur atom in its side chain and forms disulfide bonds?
- Methionine
- Cysteine (Correct answer)
- Serine
- Threonine
Correct answer: Cysteine
Cysteine's thiol (-SH) side chain can be oxidized to form disulfide (-S-S-) bonds with another cysteine, which are critical for protein tertiary and quaternary structure stabilization.
CPC CPC Biochemistry & Biological Chemistry 2
Competitive inhibition of an enzyme is characterized by: