Lecture 11

Question 1

What is a plaque assay?

Answer 1

A plaque assay is a method used to count the number of phage and/or infected cells in a culture. Plaques are clear zones that form on a bacterial lawn due to the lysis of infected cells.

Question 2

What is a one-step growth curve?

Answer 2

A one-step growth curve is used to monitor bacteriophage growth. It shows the different stages of viral replication, including the latent period and the burst size.

Question 3

Describe the replication cycle of a lytic bacterial virus.

Answer 3

The lytic cycle involves several steps: attachment to the host cell, transfer of the genome into the cell, protein synthesis (early, middle, and late genes), genome replication, assembly of mature viruses, and release from the cell (often through lysis).

Question 4

What are early genes in the lytic cycle?

Answer 4

Early genes are expressed soon after infection and often function to redirect transcription from host genes to phage genes. An example is the production of anti-sigma factors that inhibit host RNA polymerase.

Question 5

What are middle genes in the lytic cycle?

Answer 5

Middle genes are expressed after early genes and are involved in processes like replication, recombination, and nucleotide metabolism. These functions support the production of new viral genomes and components.

Question 6

What are late genes in the lytic cycle?

Answer 6

Late genes are expressed towards the end of the lytic cycle and primarily encode structural proteins for the assembly of new virions. They also include genes for proteins like holin and lysin, which facilitate the release of progeny viruses from the host cell.

Question 7

What is the restriction-modification (RM) system?

Answer 7

The RM system is an innate immune defense mechanism in bacteria that targets and degrades foreign DNA, including bacteriophage genomes.