Cell and Molecular Biology Flashcards

Which protein complex coats COPII vesicles that transport cargo from the ER to the Golgi?

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.

Which checkpoint ensures that all chromosomes are properly attached to the spindle before anaphase onset?

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.

In the lac operon, cAMP-CAP binding to the promoter is required when:

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.

What is the function of telomerase reverse transcriptase (TERT)?

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.

Which protein anchors the actin cytoskeleton to the plasma membrane at focal adhesions?

Answer: Talin

Talin links integrin cytoplasmic tails to actin filaments, forming a critical mechanical bridge at focal adhesion complexes.

Which phase of the cell cycle is characterized by centrosome duplication?

Answer: S phase

Centrosome duplication is coordinated with DNA replication and begins at the G1/S transition, completing during S phase.

In eukaryotic translation initiation, which factor is responsible for scanning the mRNA 5' UTR for the start codon?

Answer: eIF4A

eIF4A is an RNA helicase that unwinds secondary structures in the 5' UTR to facilitate ribosome scanning toward the AUG start codon.