Chapter 11

Question 1

Phage T4

Answer 1

• a complex shape, requiring many gene products for assembly
• Capsid (head): contains linear dsDNA genome
• Tail: consists of sheath plus internal tube

Question 2

T4 genome

Answer 2

a large 169 kbp genome encoding 289 proteins

Question 3

Virulent Replication of T4

Answer 3

• lytic phage
• has regulated gene expression
• early genes are transcribed by host RNA polymerase
• early genes products include DNase and a DNA polymerase
• T4 genomes are synthesized within the host cell by the T4 DNA polymerase by rolling-circle replication
• Late genes are induced to produce the capsid and tail proteins that self assemble
• late gene encodes lysozyme

Question 4

rolling-circle replication

Answer 4

• only one direction of replication

- peels off the continuous leading strand

Question 5

Adsorption to Host

Answer 5

• Phage T4 binds to E. coli by contact between its tail fibers and the outer membrane
• A conformational change causes the sheath to contract and inject the genome into the cell

Question 6

Phage Particles Self-Assemble

Answer 6

Each phage particle is assembled by convergence of three seperate pathways that produce the head, tail, and tail fibers

Question 7

Genetic dissection

Answer 7

• stages of phage assembly were discovered using strains that carry mutations in various genes that encode proteins essential for development
• Example: mutant viruses with giant heads, tails with no heads, baseplates without tails

Question 8

Conditional lethal mutations

Answer 8

Cause a lethal defect under non-permissive growth conditions
-Which allows study of the defect

But permit growth under permissive growth conditions
-Which allows growth of the phage

Question 9

Temperature-sensitive (ts) mutants

Answer 9

• Are nearly wild type (WT) and can be grown at lower temperatures, often 25C for E. coli and its phage.
• But are mutant at higher temperatures, often 42C, because the mutant protein is less stable and denatures at the higher temperature