OAT Cell and Molecular Biology 2

Question 1

Which enzyme is responsible for unwinding the DNA double helix during replication?

Accepted Answer

Helicase

Answer

Helicase breaks hydrogen bonds between base pairs to unwind the double helix at the replication fork.

Question 2

The signal recognition particle (SRP) directs ribosomes to which cellular structure?

Accepted Answer

Rough endoplasmic reticulum

Answer

SRP recognizes signal sequences on nascent polypeptides and docks the ribosome-mRNA complex to the rough ER membrane.

Question 3

Which type of RNA splicing involves the formation of a lariat intermediate?

Accepted Answer

Group II intron splicing

Answer

Group II intron self-splicing and spliceosomal pre-mRNA splicing both form a lariat intermediate via a 2'-5' phosphodiester bond.

Question 4

Which cell junction allows direct cytoplasmic communication between adjacent animal cells?

Accepted Answer

Gap junctions

Answer

Gap junctions are formed by connexin proteins that create channels allowing ions and small molecules to pass between cells.

Question 5

What is the primary role of ubiquitin in protein degradation?

Accepted Answer

It tags proteins for destruction by the proteasome

Answer

Polyubiquitin chains attached to lysine residues serve as recognition signals that target proteins for 26S proteasomal degradation.

OAT - Optometry Admission Test Practice Test