Viruses Flashcards
Suggest how these anti-viral drugs (enzyme inhibiting) would work in the treatment of patients
infected with HIV
- idea that drugs would prevent viral replication ;
- idea that T (helper) {cells / lymphocytes} will not be
{ killed / burst / destroyed}(by virus particles leaving
cell) ; - idea of {inhibition / eq} of reverse transcriptase ;
- idea that (viral) DNA could not be made;
- from the (viral) RNA ;
- idea of {inhibition / eq} of integrase ;
- idea that (viral) DNA cannot integrate into (host)
{DNA / genome} / eq ;
Suggest why common cold viruses cannot infect cells if they land on
unbroken skin.
3
- {skin / epidermis} is a barrier / eq ;
- reference to keratin ;
- reference to lack of receptors (for the virus) ;
3 enzymes are formed in the lytic cycle of norovirus, why are two of them used at the stage where new viruses are made?
3 points
- to synthesise (common cold) RNA / eq ;
- for amino acids to bind to tRNA / eq ;
- to synthesise (common cold) protein
(capsid) / eq ;
Suggest how new viral particles are formed inside the host cells.
(lytic)
5 points
- reference to synthesis of RNA ;
-
using host cell {enzymes / named enzyme
/ (RNA) nucleotides} ; - reference to synthesis of (viral) proteins ;
-
using host cell {enzymes / named enzyme
/ amino acids / ribosomes / tRNA / ATP} ; - reference to assembly of {viruses /
particles} (inside cells) ;
Why does not all contaminated food cause food poisoning?
- 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
Name two types of cell that HIV enters in the immune system.
- T helper cell
- phagocytic cells like macrophages
How does HIV enter cells?
- 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
Describe the sequence of events following infection of these cells by HIV, that
may lead to the death of the patient. [6]
- reference to viral RNA ;
- refernce to production of (viral) DNA using viral RNA as a copy
- reference to reverse transcriptase
- incorportaion of viral DNA into host cell’s DNA
- using intergrase
- reference to production of more viral RNA and proteins
- these are assembled
- infect more cells (T helper cells)
- lowers immunity to other diseases
- becuase T helper cells help in immune response
- death is caused by eg opportunistic disease like pneumonia or TB
Some anti-viral drugs prevent HIV entering the host cells.
Suggest how these anti-viral drugs could prevent HIV entering the host cells.
- idea that the drugs could {bind to / alter shape of}
{glycoproteins / gp120} ; - idea that drugs bind to {receptors / antigens} on
membrane / eq ; - called CD4 (antigen / molecules) ;
- preventing virus attaching to T (helper / CD4+) cells / eq
Describe how enzymes are involved in HIV infection.
- reverse transcriptase
- formation of viral DNA
- from viral RNA
- ref to intergrase
- intergrates the viral DNA into host DNA
- host (T helper cell) destroyed when virus particles leave cell
- more cells become infected
Why are viruses non-living?
- do not perform metabolic reactions
- do not have membrane bound organelles
- cannot replicate independantly of a host cell
Why do antibiotics not work on host cells
- viruses are non-living
- viruses do not have a cell wall (which antibiotics usually target)
lamda phage virus
- type of nucleaic acid
- presence of absence of an envelope
- arrangement of proteins in their capsid
- nucleaic acid: double stranded DNA
- envelope: absent
- proteins arrangement in capsid: complex protein capsid (non-helical)
tobacco mosiac virus
- type of nucleaic acid
- presence of absence of an envelope
- arrangement of proteins in their capsid
- nucleais acid: single stranded RNA
- envelope: absent
- proteins arrangment in capsid: helical
Ebola virus
- type of nucleaic acid
- presence of absence of an envelope
- arrangement of proteins in their capsid
- nucleaic acid: RNA single stranded
- envelope: present
- protein arrangement in capsid: helical
HIV
- type of nucleaic acid
- presence of absence of an envelope
- arrangement of proteins in their capsid
- nucleaic acid: RNA single stranded
- envelope: present
- arrangment of proteins in capside: complex
Explain why there was a delay before the number of lysed cells started to increase. (3)
- first virus has to attatch to host cells and insert its genetic material into the host
- then new viral DNA/RNA needs to be synthesised
- new proteins need to be syntheised (transcription and translation)
- new viruses must be assembled
Explain why electron micrscopes may be used to view viruses instead of light microscopes
Electron microscopes have a shorter wavelength of electrons so resolution is higher so they are better able to view viruses which are very small.
Briefly describe the lytic cycle of a virus
6 points could be 2-4 marker
- viruses attatches to host cell
- DNA/RNA synthesised
- viral proteins/capsids made
- new viruses/virions assembled
- viruses multiply
- cells lyse/burst
What is meant by ‘latency’
- virus nucleaic acid is incorporated into host cells
- virus is dormant/inactive/non virulent
- virus nucleic acid replicates when host cell divides.
Ethical implications of using untested new drug
positives;
- (ebola) has high mortality rates
- new drug may help develop it for others
negatives
- unknown side affects
- patient may not be able to provide informed consent
- it is difficult to decided who can be treated if drug is limited
What type of cells do EBV attatch to
B lymphoctes/epithelial cells
Why are viruses dependent on living cells?
2 MARKS
second mark
- unable to replicate independently
- because they do not have appropriate organelles/enzymes
Describe the lysogenic virus cycle
- virus injects host cell DNA as provirus.
- viral DNA replicates when host cell divides
- virus produces repressor proetins to inhibit transcription
- latent virus enters lytic pathway when host cell is damaged or immune system is weakened
