OAT Cell and Molecular Biology 2 — Questions and Answers
Question 1: Which enzyme is responsible for unwinding the DNA double helix during replication?
- DNA polymerase III
- Helicase (Correct answer)
- Primase
- Ligase
Correct answer: Helicase
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?
- Mitochondria
- Golgi apparatus
- Rough endoplasmic reticulum (Correct answer)
- Nucleus
Correct answer: Rough endoplasmic reticulum
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?
- Trans-splicing
- Group I intron splicing
- Group II intron splicing (Correct answer)
- tRNA splicing
Correct answer: Group II intron splicing
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?
- Tight junctions
- Desmosomes
- Gap junctions (Correct answer)
- Adherens junctions
Correct answer: Gap junctions
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?
- It catalyzes peptide bond hydrolysis
- It tags proteins for destruction by the proteasome (Correct answer)
- It unfolds misfolded proteins
- It transports proteins to lysosomes
Correct answer: It tags proteins for destruction by the proteasome
Polyubiquitin chains attached to lysine residues serve as recognition signals that target proteins for 26S proteasomal degradation.
Question 6: During mitosis, kinetochore microtubules attach to chromosomes at which structure?
- Centromere (Correct answer)
- Telomere
- Origin of replication
- Nucleosome
Correct answer: Centromere
The kinetochore is a protein complex assembled on the centromere that captures spindle microtubules during cell division.
Question 7: Which process describes the movement of a transposable element by copying itself and inserting the copy elsewhere?
- Cut-and-paste transposition
- Replicative transposition (Correct answer)
- Site-specific recombination
- Homologous recombination
Correct answer: Replicative transposition
Replicative transposition duplicates the transposable element, leaving the original in place and inserting a copy at a new site.
OAT Cell and Molecular Biology 2
Which enzyme is responsible for unwinding the DNA double helix during replication?