STP Biomedical Sciences 5 — Questions and Answers
Question 1: In a CRISPR-Cas9 experiment, what determines the sequence specificity of the cut?
- The PAM sequence alone
- The guide RNA sequence complementary to the target DNA (Correct answer)
- The size of the Cas9 protein
- The promoter driving Cas9 expression
Correct answer: The guide RNA sequence complementary to the target DNA
The ~20-nucleotide guide RNA spacer sequence base-pairs with the target DNA strand, directing Cas9 to the correct genomic locus adjacent to a PAM.
Question 2: Which immunoglobulin class is the most abundant in human serum and is capable of crossing the placenta?
- IgA
- IgM
- IgE
- IgG (Correct answer)
Correct answer: IgG
IgG is the predominant serum immunoglobulin and is actively transported across the placenta via FcRn receptors, conferring passive immunity to the fetus.
Question 3: A researcher measures increased lactate production in cancer cells even in the presence of oxygen. This phenomenon is known as:
- Oxidative phosphorylation upregulation
- The Warburg effect (Correct answer)
- Krebs cycle inhibition
- Beta-oxidation switching
Correct answer: The Warburg effect
The Warburg effect describes aerobic glycolysis in cancer cells, where glucose is preferentially converted to lactate despite sufficient oxygen.
Question 4: Which assay directly measures the affinity (Kd) of a protein-ligand interaction in real time without labeling?
- ELISA
- Surface plasmon resonance (SPR) (Correct answer)
- Co-immunoprecipitation
- Yeast two-hybrid
Correct answer: Surface plasmon resonance (SPR)
SPR measures changes in refractive index as molecules bind to an immobilized ligand on a sensor chip, providing real-time, label-free kinetic data.
Question 5: What is the function of signal recognition particle (SRP) in protein targeting?
- It degrades signal peptides after translation
- It recognizes signal sequences and arrests translation until the ribosome docks with the ER (Correct answer)
- It glycosylates proteins in the ER lumen
- It packages proteins into COPII vesicles
Correct answer: It recognizes signal sequences and arrests translation until the ribosome docks with the ER
SRP binds the emerging signal peptide and pauses translation, then delivers the ribosome-mRNA-nascent chain complex to the ER translocon.
Question 6: Which mutation type causes sickle cell disease by substituting a single amino acid in hemoglobin?
- Frameshift mutation
- Nonsense mutation
- Silent mutation
- Missense mutation (Correct answer)
Correct answer: Missense mutation
A GAG→GTG point mutation in the HBB gene causes a glutamate-to-valine substitution (E6V) — a missense mutation — producing HbS.
Question 7: In a clinical trial, which study design provides the highest level of evidence for evaluating a new therapeutic intervention?
- Case-control study
- Cross-sectional study
- Randomized controlled trial (RCT) (Correct answer)
- Cohort study
Correct answer: Randomized controlled trial (RCT)
RCTs randomly assign participants to treatment or control groups, minimizing confounding and providing the strongest causal evidence for intervention efficacy.
STP Biomedical Sciences 5
In a CRISPR-Cas9 experiment, what determines the sequence specificity of the cut?