viruses

Question 1

what are the features of a virus

Answer 1

1) unable to reproduce independently
2) carry nucleic acid within a protein shell
3) lack ribosomes so rely on host translocation machinery
4)not considered to be true living organisms

Question 2

what is a capsid

Answer 2

a proteinaceous shell made from structural subunits known as capsomers, sometimes surrpounded by an envelop of proteins, lipids and carbohydrates in which nucleic acid is carried

Question 3

outline the process of viral budding through the host plasma membrane

Answer 3

1) capsids associate with the host plasma membrane and viral glycoprotein spikes are incorporated into the membrane
2) viral nucleic acid and proteins assemble near the membrane and budding begins
3) budding continues with more spikes inserted
4) a mature viron is released

Question 4

how are viruses classified

Answer 4

1) type of nucleic acid
2) presence or absence of an envelope
3) type of host
4) size and shape

Question 5

how to viruses infect their host

Answer 5

1) attaches to cell
2) inserts viral nucelic acid
3) lytic. Lysogenic cycle

Question 6

what is the lytic cycle

Answer 6

when viral nucleic acid enters the host cell it is replicated produced viral proteins which eventually are released from the cell by lysis

Question 7

what is the lysogenic cycle

Answer 7

when viral nucleic acid enters the host cell the viral genome is integrated into the host genome

Question 8

outline the process of viral nucleic acid entering the cell

Answer 8

1) bump into the host
2) attachment requires specific conditions but no energy, if successfull it is absorbed
3) ligands on the surface of the virus binds to cell receptors and enters the cell

Question 9

outline how double stranded DNA viruses replicate

Answer 9

• they have their own DNA polymerase so the infecting virus can be transcribed and translated by the host directly

Question 10

outline how single stranded DNA viruses replicate

Answer 10

• they need to require a complementary strand to form double stranded DNA with the host DNA polymerase
• this allows transcription and translation by the host replicating viral DNA which is then converted back to ssDNA before packaging

Question 11

outline how single stranded, sense (+) RNA viruses replicate

Answer 11

1) +ssRNA can be translated directly as it can be read as mRNA by the host OR it can be replicated and act as a genome
2) if it is being replicated +ssRNA and the RNA replicase produced -ssRNA which is uses as the replicating form so RNA replicase produces more +ssRNA which is then dispersed (it acts as a template)

Question 12

outline how -ssRNA is replicated

Answer 12

1) -ssRNA cant be directly translated as it cant be read by host as mRNA therefore must be converted for both replication and translation
2)-ssRNA and RNA replicase produce +ssRNA strand
3) this +ssRNA strand is uses as a template so when paired with RNA replicase it produces more -ssRNA which is then dispersed

Question 13

what is a retrovirus

Answer 13

a virus which uses RNA as its genetic material and when it infects a cell it makes a DNA copy of its genome which is inserted into the DNA of host

Question 14

outline virion assembly for non-enveloped viruses

Answer 14

1) viral capsomers self assemble forming a capsid
2) viral DNA is packed into the capsid
3) in phages the tail and tail fibres are assembled
4) viral proteins degrade the cell membrane and the virons are released

Question 15

outline how phage’s degrade the cell membrane for release

Answer 15

1) holins make pores in the cell membrane
2) enlysisns degrade the peptidoglycan layer
3) the outermembrane bursts due to internal osmotic pressure
4) the cell membrane is debilitated

Question 16

outline how enveloped viruses are released from the cell

Answer 16

1) virion capsomers self assemplt forming the capsid
2) viral DNA packaged in the capside
3) virus released by budding

Question 17

what is the difference between the release of enveloped and non-enveloped virion

Answer 17

enveloped do not damage the cell therefore cells live longer and produce more virion

Question 18

outline how the antiviral therapy acylovir works

Answer 18

• a synthetic analogue of guanosine
  it works by blocking the elongation of viral DNA by the virus encoded DNA polyermase

Question 19

what is Acyclovir

Answer 19

aka zovirax= an antiviral therpay which is effective against herpesvirus

Question 20

outline what HIV drugs can inhibit

Answer 20

1) reverse transcriptase inhibitors = prevents RNA into DNA
2) protease inhibitors= prevents cleavage of polypeptides into smaller protons needed for virion assembly
3) integrase inhibtors= stops the insertion o fgenomic DNA into host chromosome
4) entry inhibitors= prevents binding to cell membrane

Question 21

what happens when a new strain arises

Answer 21

a result of mutations

Question 22

what is antigenic drift

Answer 22

a mutation consiting of small changes in the virus

Question 23

what is antigenic shift

Answer 23

a mutation resulting in an abrupt shift and major changes

Question 24

why do RNA viruses mutate faster than DNA viruses

Answer 24

1) no RNA repair mechansims
2) RNA replicase does not have proofreading activity like most DNA ploymerases

Question 25

what is horizontal gene transfer

Answer 25

the movement of genetic material between organisms

Question 26

outline horizontal gene transfer

Answer 26

the process in which bacterial DNA is moved from one bacterium to another by a virus
during synthesis of new phages the phage incorporates some host DMA
infecting a new host incorporates the pahe and previous host DNA into the new host