Viruses

Question 1

viruses are akaryotic what does this mean

Answer 1

Cells that dont have a nucleus - viruses are also acellular

Question 2

Size of Viruses

Answer 2

2 - 200 nanometres

Question 3

They are obligate

Answer 3

Requires host cell to survive and does not contain any machinery of its own (no protein synthesis or ATP production)

Question 4

Viruses have single/double stranded DNA - it is very short…why?

Answer 4

Because it only contains information about components of virus - does not need information to build organelles

Question 5

Can viruses switch from using RNA to DNA?

Answer 5

Yes - they can use one at different stages of their development - only one can be used at a time.

Question 6

All viruses have…

Answer 6

Nucleic acid core inside a protein coat/capsid. Capsids can either be icosahedral or helical and is made from capsomeres

Question 7

some viruses have…

Answer 7

Envelopes and tails (bacteriophages)

Question 8

icosahedral

Answer 8

20 triangular faces, 30 sides and 12 vertices - capsomeres can be pentameres or hexameres

Question 9

Capsomeres subunits per face

Answer 9

3

Question 10

Helical

Answer 10

protein subunits bind to nucleotides of DNA/RNA making a long continuous chain - can contain more than one type of subunit - it is very stable but is able to assosciate and disassosciate depending on environment

Question 11

Viral replication

Answer 11

Viron attaches to membrane of virus and penetrates it to injuect the viral DNA into the cytoplasm of cell. Then proteins and nuclic acids needed for virus is synthesised using the cells ribosomes and enzymes. Then more virons are assembled and packaged inside capsid then the cell erupts and the virons are released.

Question 12

Why are only specific cells in danger from a particular type of virus?

Answer 12

Because the virus has proteins which bind to a receptor on the cell membrane - that is how they gain entry to the cell

Question 13

Viral replication can be monitored using…

Answer 13

Plaque formation - it is formed when infected cell undergoes lysis

Question 14

Methods of Virus Transmission

Answer 14

Respiratory - Influenza 
Faecal - oral - enterovirus
Blood-borne - hepatitis B 
Sexual - HIV 
Animal/Insect - Rabies

Question 15

what is tissue tropism?

Answer 15

when a cell/tissue supports the growth of a particular virus - some viruses will only infect these particular cells this is done by receptor recognition.

Question 16

What is viraemia?

Answer 16

It is the widespread viral infection of tissues

Question 17

Influenza Virus Structure + Features

Answer 17

Single stranded RNA 
Has envelope 
Helical capsid
Infects animals and humans 
Destruction of respiratory epithelial cells which can lead to bacteria infection and alters cytokine expression so leads to fever

Question 18

Two groups of anti-virals

Answer 18

Anti-viral drugs - treats all infections apart from those caused by HIV
Antiretrovirals - treats infections caused by HIV

Question 19

Antivirals work by…

Answer 19

Interfere with viral nucleic acid synthesis
Stop them binding to cells
Stimulate immune responses

Question 20

Antivirals that fight Influenza

Answer 20

Amantadine - blocks ion channels - used t prevent not cure

Oseltamivir & Zanamivir - inhibits enzyme found on envelope of virus - reduces duration of illness

Question 21

Acyclovir

Answer 21

Treats herpes (oral and genital) and chickenpox - prevents DNA synthesis

Question 22

HAART - Highly active retroviral therapy

abacavir, delavirdine, didanosine, lamivudine, stavudine, tenofovir

Answer 22

3 different drugs used - uses reverse transcriptase inhibitors - prevents production of new viral DNA