Virus previous exam qs

Question 1

What is virus latency? What is recrudesnce of latent virus? Give example of latent virus

Answer 1

Virus latency is a viruses ability to stay inert in a cell, meaning that once a cell is infected by a virus the virus will always remain dormant in cell.
Recrudescence of latent virus is the reactivation of an latent virus usually due to stress
Herpes

Question 2

Describe the first 3 stages of virus replication

Answer 2

Adsoprtion - non specific random binding to surface of cell
Attachment - specific binding of ligand of virus to host cell receptor molecule
Penetration - receptor cell endocytosis or nuclear fusion of virus into plasma membrane

Question 3

Describe the last 4 stages of virus replication

Answer 3

Uncoating - release of nucleic acid from capsid into cell, release of lysogenic enzymes into cytoplasmic vacuoles
Synthesis - synthesis of protein and nucleic acid in cell
Assemble - assembling of virus (self assemble)
Release - budding or cell lysis

Question 4

Describe Active immunity

Answer 4

Can be natural (over life time) or artificial (vaccines), can be temporal or life long. Allows host immune system to fight foreign cells

Question 5

Describe passive immunity

Answer 5

Can be natural (placenta) or artifical (anti-serum), can only be temporal (3 weeks). Host immune system cant fight foreign cells

Question 6

List antiviral drugs which can be used to affect some stages of virus replication

Answer 6

Antibodies can be used to block attachment of HIV
Amanditane can stop uncoating of influenza
Neurominidase inhibitors can stop release of influenza

Question 7

On what bases are animal viruses classified part 1 (RNA/DNA etc)

Answer 7

RNA/DNA nucleic acid
Symmetry
non/enveloped
\+ or - sense (RNA)
non/segmented
linear/circular
double strand or single strand

Question 8

On what bases are animal viruses classified part 2 (order etc)

Answer 8

Order
Family
Sub family
species
sub species
genus
strain 
variant

Question 9

Describe main characteristics of extracellular phase of virus

Answer 9

Extracellular virus is fragile, the virus can’t live without the host cell and the virus is metabolically inert

Question 10

Describe the main characteristics of intracellular phase of virus

Answer 10

Intracellular virus thrives, takes over the cells machinery, forces cell to replicate virus and disease may occur

Question 11

Describe Antigenic drift

Answer 11

Antigenic drift is a point mutation which changes the loop surrounding the receptor molecule of haemagglutinin or in the catalytic site of neurominidase

Question 12

Describe antigenic shift

Answer 12

Antigenic shift is a change in subtype of haemagglutinin/neurominidase due to a point mutation or genetic reassortment.

Question 13

Describe the lytic cycle

Answer 13

Lytic cycle is where a phage attaches to a cell, releases nucleic acid into the host cell and takes over the cells machinery, forcing the cell to replicate the virus then makes the cell explode by cell lysis

Question 14

Describe the lysogenic cycle

Answer 14

Lysogenic cycle is where a phage attaches to a cell, releases its nucleic acid into host bacteria chromosome, allows the cell to replicate so when it replicates the cells contain the viral DNA in host genome

Question 15

Describe Innate immunity

Answer 15

Innate immunity is immunity you are born with, it is the first and second line of defence of the immune system. It is non-specific and has no memory

Question 16

Describe adaptive immunity

Answer 16

Adaptive immunity is immunity an organism develops over a life time, it may be acquired naturally or artificially, it is the 3rd line of defence of the immune system and has memory and is specific.

Question 17

What is a pandemic?

Answer 17

A pandemic is a where a virus/disease affects a country or the world

Question 18

Describe the 1st line of defence

Answer 18

First line of defence is skin and mucous membranes. Skin protects from outside and can be secreted and mucous traps foreign cells and can force coughing and sneezing, fever also occurs to increase metabolic rate of immune system

Question 19

Describe 2nd line of defence

Answer 19

2nd line of defence is phagocytes, lymphatic system and inflammation. Phagocytes eat and kill foreign cells and can be neutrophils (first to arrive at scene) and macrophages (bigger later on). Inflammation can destroy/confide infectious agents and the lymphatic system takes fluid from inflammation and puts it back into blood

Question 20

Describe the 3rd line of defence

Answer 20

3rd line of defence has two arms. T arm provides immunity inside host cell, t cells recognise foreign cells and recruit other cells (phagocytes) to kill.
B arm uses antibodies to kill antigens in extracellular fluid, B cells (plasma) interact with pathogen and check with T(h) cells to make sure pathogen is bad and then makes antibodies to kill.