OAT Cell and Molecular Biology 4 — Questions and Answers
Question 1: Which protein complex coats COPII vesicles that transport cargo from the ER to the Golgi?
- Clathrin
- COPI coat proteins
- Sec23/Sec24 and Sec13/Sec31 (Correct answer)
- Retromer complex
Correct answer: Sec23/Sec24 and Sec13/Sec31
COPII vesicles are coated by the Sec23/Sec24 inner layer and Sec13/Sec31 outer cage, driven by the small GTPase Sar1.
Question 2: Which checkpoint ensures that all chromosomes are properly attached to the spindle before anaphase onset?
- G1/S checkpoint
- DNA damage checkpoint
- Spindle assembly checkpoint (SAC) (Correct answer)
- G2/M checkpoint
Correct answer: Spindle assembly checkpoint (SAC)
The SAC monitors kinetochore-microtubule attachment and inhibits the APC/C via the mitotic checkpoint complex until all chromosomes are bi-oriented.
Question 3: In the lac operon, cAMP-CAP binding to the promoter is required when:
- Lactose is absent and glucose is present
- Lactose is present and glucose is absent (Correct answer)
- Both glucose and lactose are present
- Both glucose and lactose are absent
Correct answer: Lactose is present and glucose is absent
Low glucose causes cAMP to accumulate; cAMP-CAP binding to the lac promoter is needed for maximal transcription when lactose is the carbon source.
Question 4: What is the function of telomerase reverse transcriptase (TERT)?
- It repairs double-strand breaks using a template
- It synthesizes telomeric repeats using an RNA template it carries (Correct answer)
- It degrades the RNA primer at the 5' end of chromosomes
- It unwinds the G-quadruplex at telomeres
Correct answer: It synthesizes telomeric repeats using an RNA template it carries
Telomerase uses its built-in RNA component (TERC) as a template to extend the 3' G-rich overhang of linear chromosomes.
Question 5: Which protein anchors the actin cytoskeleton to the plasma membrane at focal adhesions?
- Spectrin
- Talin (Correct answer)
- Dystrophin
- Ankyrin
Correct answer: Talin
Talin links integrin cytoplasmic tails to actin filaments, forming a critical mechanical bridge at focal adhesion complexes.
Question 6: Which phase of the cell cycle is characterized by centrosome duplication?
- G1 phase
- S phase (Correct answer)
- G2 phase
- M phase
Correct answer: S phase
Centrosome duplication is coordinated with DNA replication and begins at the G1/S transition, completing during S phase.
Question 7: In eukaryotic translation initiation, which factor is responsible for scanning the mRNA 5' UTR for the start codon?
- eIF2
- eIF4A (Correct answer)
- eIF4G
- eIF1A
Correct answer: eIF4A
eIF4A is an RNA helicase that unwinds secondary structures in the 5' UTR to facilitate ribosome scanning toward the AUG start codon.
OAT Cell and Molecular Biology 4
Which protein complex coats COPII vesicles that transport cargo from the ER to the Golgi?