Lecture 5

Question 1

What are the two types of cycle used by bacteriophage?

Answer 1

Lytic cycle - Phage replicates and causes cell lysis to escape

Lysogenic cycle - Phage integrated its DNA into bacteria. DNA can be passed onto daughter cells. During stress phage will replicate and cause lysis to leave

Question 2

Outline the actions of the T4 lysis proteins

Answer 2

Holin T accumulates and forms a multimer at correct time in inner membrane

Endolysin will pass through the Holin T multimer and degrade the peptidoglycan

SPANINS can then diffuse freely to outer membrane and inner membrane and lead to lysis

Question 3

How is lysis controlled during the lysogenic cycle?

Answer 3

Antiholin stops holin multimerising

Question 4

Outline phi 6 lysis

Answer 4

• P8 attaches to prohead of nucleocapsid
• P3 spike protein assembled in the membrane via P6
• P9 and P12 induce vesicularisation of the membrane around the nucleocapsid
• Lysin P5 and membrane protein P10 cause lysis

Question 5

Name a phage which can exit a cell without causing lysis

Outline its action to exit

Answer 5

M13

• Prophage of twisted single stranded closed cicular DNA coated with gp5
• Gp5interacts with gp1 in membrane which triggers opening of extrusion channel, through gp4
• gp5 swapped for gp8 and gp3, 6, 7, 9 added to ends of the phage (all from inner membrane of the bacteria)
• Mature phage is released

Question 6

What is commonly used by animal virus for lysis?

Answer 6

Viroporins - encoded by late virus genes and form pores in the membrane

Question 7

What stratergy is used by baculoviridae?

Why?

Answer 7

Occulusion body - polyhedrin coat around more than one capsid

Infects anthropods and crustaceans, and hence are more resistant to environment and can infect via ingestion

Question 8

How do enveloped animal viruses exit the cell?

Answer 8

Budding

Question 9

Where does the envelope around enveloped animal virus come from?

Answer 9

The membrane of the cell

Question 10

Why do different viruses have different sites of budding?

Answer 10

Different requirements for the enveloped fulfilled by different membrane types

Question 11

Where in the cell can viruses bud from?

Answer 11

• Plasma membrane - retroviruses, filoviruses
• Golgi - Herpesvirus, poxvirus
• Nucleus - used to travel through ER for golgi or ER membrane envelopes
• ER -HCV
• Mitochondria - HCV

Question 12

How is budding both push and pull?

Answer 12

• Viral membrane glycoprotein assembly in outer membrane pulls membrane out
• Innner viral proteins and nucleocapsid pushes membrane out

Question 13

Ouline influenza virus budding

Answer 13

1. HA and NA cluster in lipid rafts
2. M1 binds to cytoplasmic tails of HA and NA and acts as binding site for vRNP’s
3. Polymerization of M1 causes elongation
4. M2 is recruited and causes scission at the bottom of envelope

Question 14

How is M2 hypothesised to work?

Answer 14

M2, a viroporin, is targeted to viral budding sites by binding cholesterol

Acting as a proton channel the M2 reduces the electrical repulsion between opposing monolayers of the membrane to allow budding

Question 15

What is required to allow budding through different membranes?

Answer 15

Different viroporins

Question 16

What is the viroplasm?

Answer 16

An electron dense cytoplasmic rich inclusion formed by large DNA viruses and dsRNA viruses

Question 17

What are spherules?

Answer 17

50-400nm membrane invaginations found in several different membrane bound organelles

Question 18

What are double membrane vesicles?

Answer 18

Membraneous structures derived from ER or golgi having a diameter of 200-300nm

Question 19

What are nuclear virl factories?

Answer 19

Sub nuclear compartments formed by some viruses for replication

e. g. Herpes simplex - the replication compartment
e. g. Baculoviruses - virogenic stroma

Question 20

What is the difference between HBV and HCV?

Answer 20

Both cause liver damage but HBV cuases liver disease and cancer whereas HCV causes liver transplant

HCV can’t be detected as well and is a lipoviroparticle

Question 21

What is HCV dependent on for production?

Answer 21

Hepatic very-low density lipoproteins

Question 22

What does HCV use for attachment?

What is required for its internalisation?

Answer 22

Heparin sulphate

The LDL receptor

Question 23

Where does the viral replication complex of HCV form?

What is essential for this formation?

Answer 23

The ER

A poly protein of structural and non-structural proteins inserted into the membrane which curves the membrane and acts as scaffold for RC assembly

Question 24

Why does HCV infect liver cells?

Answer 24

The RC is located next to wher lipid doplets are being formed to encapsulated the capsid in the droplet and have glycoproteins on the outside

These lipid droplets are formed in liver cells

Question 25

Why does HCV need to exit via the golgi?

Answer 25

To mature into an infectious particle

Question 26

Where does HIV assemble its capsid?

Answer 26

At the site of Budding

Question 27

Oultine HIV budding

Answer 27

• gp120 and gp41 produced and inserted into membrane
• Gag interacts with these proteins to start budding
• Gag interacts with cellular ESCRT machinery
• Ap2 restricts Gag to membrane and interaction between Ap1 and ESCRT causes budding
• A coat of clathiring is also incorporated under the envelope
• Tetherin hold the viral particle on the cell membrane in an attempt to alert the immune system
• Ap2 and clathirin then removes tetherin

Question 28

How id HIV matured?

Answer 28

Viral protease cleaves Gag and Gag-Pol to form mature proteins