STP Biomedical Sciences 4

Question 1

Which phase of the cell cycle is characterized by centrosome duplication and the cell committing to division past the restriction point?

Accepted Answer

G1 phase

Answer

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?

Accepted Answer

H3K27 trimethylation

Answer

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?

Accepted Answer

Phagocytosis of bacteria

Answer

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?

Accepted Answer

Sanger sequencing

Answer

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?

Accepted Answer

Lentiviruses can infect non-dividing cells and integrate stably into the genome

Answer

Lentiviral vectors integrate into host chromatin and can transduce non-dividing cells, enabling long-term transgene expression.

(STP) Scientist Training Programme Practice Test