OAT Cell and Molecular Biology 5 — Questions and Answers
Question 1: Which mutation type results in the substitution of one amino acid for another without altering the reading frame?
- Nonsense mutation
- Frameshift mutation
- Missense mutation (Correct answer)
- Silent mutation
Correct answer: Missense mutation
A missense mutation changes a single nucleotide so that a different amino acid is incorporated into the polypeptide chain.
Question 2: Which model best explains how pioneer transcription factors access nucleosome-occluded DNA?
- They require prior histone eviction by SWI/SNF
- They bind DNA within the nucleosome without full displacement (Correct answer)
- They rely on DNA methylation to expose binding sites
- They only bind during S phase when nucleosomes are disassembled
Correct answer: They bind DNA within the nucleosome without full displacement
Pioneer factors like FOXA1 can engage their motifs within partially assembled nucleosomes, subsequently recruiting remodelers to open chromatin.
Question 3: The sodium-potassium ATPase transports ions against their concentration gradients in which stoichiometry?
- 2 Na⁺ out, 3 K⁺ in
- 3 Na⁺ out, 2 K⁺ in (Correct answer)
- 2 Na⁺ in, 3 K⁺ out
- 1 Na⁺ out, 1 K⁺ in
Correct answer: 3 Na⁺ out, 2 K⁺ in
Each cycle of the Na⁺/K⁺-ATPase exports 3 sodium ions and imports 2 potassium ions, consuming one ATP molecule.
Question 4: Which DNA repair pathway corrects mismatched bases introduced during DNA replication?
- Base excision repair (BER)
- Nucleotide excision repair (NER)
- Mismatch repair (MMR) (Correct answer)
- Non-homologous end joining (NHEJ)
Correct answer: Mismatch repair (MMR)
Mismatch repair proteins (e.g., MutS, MutL homologs) recognize mismatched bases and excise a stretch of the newly synthesized strand for resynthesis.
Question 5: What distinguishes necrosis from apoptosis at the cellular level?
- Necrosis produces apoptotic bodies; apoptosis causes cell swelling
- Necrosis involves cell swelling and membrane rupture; apoptosis is orderly with membrane blebbing (Correct answer)
- Necrosis requires caspase activation; apoptosis does not
- Necrosis is programmed; apoptosis is always accidental
Correct answer: Necrosis involves cell swelling and membrane rupture; apoptosis is orderly with membrane blebbing
Necrosis is characterized by cell swelling and plasma membrane rupture causing inflammation, while apoptosis is an organized, caspase-dependent process producing apoptotic bodies.
Question 6: Which small non-coding RNA class guides Argonaute proteins to silence target mRNAs post-transcriptionally?
- snRNA
- snoRNA
- miRNA (Correct answer)
- rRNA
Correct answer: miRNA
microRNAs (miRNAs) associate with RISC (RNA-induced silencing complex) and base-pair with complementary sequences in target mRNA 3' UTRs to repress translation or promote degradation.
Question 7: Which property of the plasma membrane is primarily responsible for its selective permeability to small nonpolar molecules?
- Presence of aquaporin channels
- The hydrophobic lipid bilayer core (Correct answer)
- Negative surface charge from phospholipid head groups
- High cholesterol content stiffening the membrane
Correct answer: The hydrophobic lipid bilayer core
Small nonpolar molecules dissolve readily in the hydrophobic interior of the bilayer and diffuse across without requiring protein channels.
OAT Cell and Molecular Biology 5
Which mutation type results in the substitution of one amino acid for another without altering the reading frame?