Viruses

Question 1

Suggest how these anti-viral drugs (enzyme inhibiting) would work in the treatment of patients
infected with HIV

Answer 1

1. idea that drugs would prevent viral replication ;
2. idea that T (helper) {cells / lymphocytes} will not be
   { killed / burst / destroyed}(by virus particles leaving
   cell) ;
3. idea of {inhibition / eq} of reverse transcriptase ;
4. idea that (viral) DNA could not be made;
5. from the (viral) RNA ;
6. idea of {inhibition / eq} of integrase ;
7. idea that (viral) DNA cannot integrate into (host)
   {DNA / genome} / eq ;

Question 2

Suggest why common cold viruses cannot infect cells if they land on
unbroken skin.

Answer 2

1. {skin / epidermis} is a barrier / eq ;
2. reference to keratin ;
3. reference to lack of receptors (for the virus) ;

Question 3

3 enzymes are formed in the lytic cycle of norovirus, why are two of them used at the stage where new viruses are made?

Answer 3

1. to synthesise (common cold) RNA / eq ;
2. for amino acids to bind to tRNA / eq ;
3. to synthesise (common cold) protein
   (capsid) / eq ;

Question 4

Suggest how new viral particles are formed inside the host cells.
(lytic)

Answer 4

1. reference to synthesis of RNA ;
2. using host cell {enzymes / named enzyme
   / (RNA) nucleotides} ;
3. reference to synthesis of (viral) proteins ;
4. using host cell {enzymes / named enzyme
   / amino acids / ribosomes / tRNA / ATP} ;
5. reference to assembly of {viruses /
   particles} (inside cells) ;

Question 5

Why does not all contaminated food cause food poisoning?

Answer 5

• enzymes kill microorangisms
• stomach acid kills microorganisms
• lack of oxygen for microorganisms
• competition with gut flora
• insufficient numbers of microorganisms to cause food poisoning
• ## immediate vomitting removes microorganisms

Question 6

Name two types of cell that HIV enters in the immune system.

Answer 6

1. T helper cell
2. phagocytic cells like macrophages

Question 7

How does HIV enter cells?

Answer 7

• HIV has glycoproteins on it’s surface which recognise and bind to the CD4 receptors of the cell (T helper/ phagocytic cell)
• virus envelope fuses with the cell surface membrane

Question 8

Describe the sequence of events following infection of these cells by HIV, that
may lead to the death of the patient. [6]

Answer 8

1. reference to viral RNA ;
2. refernce to production of (viral) DNA using viral RNA as a copy
3. reference to reverse transcriptase
4. incorportaion of viral DNA into host cell’s DNA
5. using intergrase
6. reference to production of more viral RNA and proteins
7. these are assembled
8. infect more cells (T helper cells)
9. lowers immunity to other diseases
10. becuase T helper cells help in immune response
11. death is caused by eg opportunistic disease like pneumonia or TB

Question 9

Some anti-viral drugs prevent HIV entering the host cells.
Suggest how these anti-viral drugs could prevent HIV entering the host cells.

Answer 9

1. idea that the drugs could {bind to / alter shape of}
   {glycoproteins / gp120} ;
2. idea that drugs bind to {receptors / antigens} on
   membrane / eq ;
3. called CD4 (antigen / molecules) ;
4. preventing virus attaching to T (helper / CD4+) cells / eq

Question 10

Describe how enzymes are involved in HIV infection.

Answer 10

1. reverse transcriptase
2. formation of viral DNA
3. from viral RNA
4. ref to intergrase
5. intergrates the viral DNA into host DNA
6. host (T helper cell) destroyed when virus particles leave cell
7. more cells become infected