CPC CPC Biochemistry & Biological Chemistry 1 ā Questions and Answers
Question 1: Which bond type is primarily responsible for the secondary structure (Ī±-helix and Ī²-sheet) of proteins?
- Disulfide bonds
- Hydrogen bonds between backbone NH and C=O groups (Correct answer)
- Hydrophobic interactions
- Ionic bonds between charged side chains
Correct answer: Hydrogen bonds between backbone NH and C=O groups
Secondary structures are stabilized by hydrogen bonds between the peptide backbone's NH groups and carbonyl (C=O) groups at regular intervals along the chain, forming Ī±-helices and Ī²-sheets.
Question 2: In enzyme kinetics, the Michaelis constant (Km) represents:
- Maximum reaction velocity
- Substrate concentration at which reaction velocity is half of Vmax (Correct answer)
- Inhibitor concentration that halves enzyme activity
- The equilibrium constant for enzyme-product formation
Correct answer: Substrate concentration at which reaction velocity is half of Vmax
Km is the substrate concentration [S] at which the reaction velocity equals Vmax/2; a low Km indicates high enzyme affinity for the substrate.
Question 3: Which nucleotide base pairs with adenine (A) in DNA?
- Cytosine (C)
- Guanine (G)
- Thymine (T) (Correct answer)
- Uracil (U)
Correct answer: Thymine (T)
In DNA, adenine pairs with thymine via two hydrogen bonds (A=T), while guanine pairs with cytosine via three hydrogen bonds (Gā”C), following Chargaff's base pairing rules.
Question 4: The citric acid cycle (Krebs cycle) primarily occurs in which cellular compartment?
- Cytoplasm
- Nucleus
- Mitochondrial matrix (Correct answer)
- Endoplasmic reticulum
Correct answer: Mitochondrial matrix
The citric acid cycle takes place in the mitochondrial matrix, where acetyl-CoA (from pyruvate oxidation) is fully oxidized to CO2, generating NADH, FADH2, and GTP.
Question 5: Which lipid class forms the basic structural component of biological cell membranes?
- Triglycerides
- Sterols (cholesterol)
- Phospholipids (Correct answer)
- Waxes
Correct answer: Phospholipids
Phospholipids form the lipid bilayer of cell membranes due to their amphipathic nature: hydrophilic phosphate head groups face aqueous environments while hydrophobic fatty acid tails face inward.
Question 6: The Southern blot technique is used to detect:
- Specific proteins in a mixture
- Specific DNA sequences in a sample (Correct answer)
- RNA transcripts
- Lipids in tissue extracts
Correct answer: Specific DNA sequences in a sample
Southern blotting separates DNA fragments by gel electrophoresis, transfers them to a membrane, and uses a labeled complementary probe to detect specific DNA sequences by hybridization.
CPC CPC Biochemistry & Biological Chemistry 1
Which bond type is primarily responsible for the secondary structure (Ī±-helix and Ī²-sheet) of proteins?