STP Biomedical Sciences 4 — Questions and Answers
Question 1: Which phase of the cell cycle is characterized by centrosome duplication and the cell committing to division past the restriction point?
- G0
- S phase
- G1 phase (Correct answer)
- G2 phase
Correct answer: G1 phase
During G1, cells grow, centrosome duplication begins, and passage through the restriction point commits the cell to completing division.
Question 2: Which epigenetic modification is most directly associated with transcriptional silencing?
- H3K4 trimethylation
- H3K27 trimethylation (Correct answer)
- H3K9 acetylation
- H4K16 acetylation
Correct answer: H3K27 trimethylation
H3K27me3, catalyzed by the PRC2 complex, is a hallmark of facultative heterochromatin and transcriptional repression.
Question 3: A gene knockout mouse lacks functional macrophages. Which process of innate immunity would be most directly impaired?
- Antibody production
- Complement synthesis
- Phagocytosis of bacteria (Correct answer)
- T cell activation in lymph nodes
Correct answer: Phagocytosis of bacteria
Macrophages are professional phagocytes; their absence severely impairs phagocytic clearance of pathogens and debris.
Question 4: Which technique uses chain-terminating dideoxynucleotides to determine DNA sequence?
- Pyrosequencing
- Sanger sequencing (Correct answer)
- Illumina sequencing by synthesis
- Nanopore sequencing
Correct answer: Sanger sequencing
Sanger sequencing incorporates ddNTPs that lack a 3'-OH group, terminating chain elongation at specific bases to generate length-sorted fragments.
Question 5: What is the main advantage of using a lentiviral vector over an adenoviral vector for gene therapy?
- Lentiviruses can infect non-dividing cells and integrate stably into the genome (Correct answer)
- Lentiviruses have a larger packaging capacity
- Lentiviruses do not integrate into the host genome
- Lentiviruses provoke a stronger immune response
Correct answer: Lentiviruses can infect non-dividing cells and integrate stably into the genome
Lentiviral vectors integrate into host chromatin and can transduce non-dividing cells, enabling long-term transgene expression.
Question 6: Which statistical test is most appropriate for comparing the means of three or more independent groups?
- Paired t-test
- Chi-square test
- One-way ANOVA (Correct answer)
- Mann-Whitney U test
Correct answer: One-way ANOVA
One-way ANOVA tests whether means differ across three or more independent groups while controlling the family-wise error rate.
Question 7: Which protein domain is responsible for recognizing phosphotyrosine residues in receptor tyrosine kinase signaling?
- SH2 domain (Correct answer)
- SH3 domain
- PH domain
- RING domain
Correct answer: SH2 domain
SH2 (Src Homology 2) domains bind specifically to phosphorylated tyrosine residues, enabling downstream signal transduction.
STP Biomedical Sciences 4
Which phase of the cell cycle is characterized by centrosome duplication and the cell committing to division past the restriction point?