Viruses

Question 1

Viruses can be described as obligate intracellular parasites because . . .

Answer 1

they can only exist and reproduce as parasites in the cells of other living organisms. Viruses need to invade and overtake living cells in order to reproduce.

Question 2

Capsomeres are repeating _______ units that make up the _________ of a virus

Answer 2

Capsomeres are repeating protein units that make up the capsid of a virus.

Question 3

can we use antibiotics on viruses?

Answer 3

no because they are not living cells thus antivirals must work by inhibiting virus replication

Question 4

what are some ways antivirals can work against viruses

Answer 4

target receptors by which viruses recognise host cells by

target the enzymes that help to translate or replicate the viral DNA or RNA

inhibit the protease enzymes that enable new virus particles to bud from host membranes

Question 5

in disease control of viruses the main focus should be on preventing __________

Answer 5

in disease control of viruses the main focus should be on preventing spread

Question 6

Identify 6 ways of controlling spread of a disease

Answer 6

rapid identification of disease

nursing in isolation

preventing transmission from one individual to another

sterilizing or disposing of equipment and bedding after use

the wearing of protective clothing by health workers

identifying contacts

Question 7

describe the stages of the drug development process

Answer 7

early phase research- testing on cell cultures
preclinical testing-animal testing
clinical trials-human testing
regulation review
scale up manufacturing

Question 8

ethical implications behind fast tracked drugs

Answer 8

severity of disease

availability of any other treatments for the disease

effectiveness of standard disease control measures in halting the spread of the disease

transparency about the process and informed consent of those given the treatment

freedom of choice over participation

involvement of affected community- sometimes overall .. community treatment may be more valuable than individual consent

Question 9

reasons against using untested drugs

Answer 9

unexpected side effects that can make the situation worse

informed consent is difficult to obtain if the ill have lower levels of education

Question 10

State the 2 routes of virus infection and describe the differences between them

Answer 10

LATENCY-LYSOGENIC PATHWAY

DNA is inserted into host cell (aka provirus) and is replicated every time the cell divides. This does not affect the host cell. The virus is part of the host cell but can be said to be latent.(non-virulent).

Messenger RNA is not produced because one of the viral genes causes the production of repressor proteins which makes it impossible to translate the rest of the viral genetic material

THE LYTIC PATHWAY
Viral genetic material is replicated independently of the host DNA straight after entering the host.

Mature viruses are made and eventually the host bursts, releasing large numbers of new virus particles that can invade other cells.- the amount of repressor protein decreases and the viruses enter the lytic stages in their life and become virulent (disease causing)

some viruses have both latent and lytic stages in their life cycles

Question 11

define retrovirus

Answer 11

special type of RNA virus that control the production of DNA corresponding to the viral RNA genome

Question 12

_________ ___________ is a special type of enzyme synthesised in the life cycle of a retrovirus that makes DNA molecules corresponding to the viral RNA genome.

Answer 12

REVERSE TRANSCRIPTASE is a special type of enzyme synthesised in the life cycle of a retrovirus that makes DNA molecules corresponding to the viral RNA genome.

The single strand of viral RNA directs the synthesis of the enzyme which goes on to make DNA molecules corresponding to the viral genome. This DNA is then incorporated into the host cells DNA and is used as a template for new viral proteins and ultimately a new viral RNA genome

Question 13

A ________ is the DNA that is inserted into the host cell during the lysogenic pathway of reproduction in viruses

Answer 13

A PROVIRUS is the DNA that is inserted into the host cell during the lysogenic pathway of reproduction in viruses

Question 14

State the term used to describe a microorganism that is disease-causing

Answer 14

VIRULENT

Question 15

What are VAPS

Answer 15

virus attachment particles - specific proteins (antigens) that target proteins in the host cell surface membrane.

Question 16

Adaptations of viruses

Answer 16

CAPSID-protein coat made up of simple repeating units known as capsomeres. This minimises the amount of genetic material needed to code for the coat.

LIPID ENVELOPE produced from host cell covering capsid- makes it easier for viruses to pass from cell to cell

Capsid contains genetic material-when digested by cell it releases the viral genetic material

Question 17

How are viruses classified

Answer 17

classified by genome and type of replication and double/single stranded nucleic acid.

Question 18

identify 2 forms of viruses and describe them

Answer 18

RNA viruses-Genetic material is RNA. In positive ssRNA viruses- RNA acts directly as mRNA and can be translated at the ribosomes

DNA viruses-Negative ssRNA viruses cannot be directly translated. RNA strand firstly needs to be transcribed before it is translated at the ribosomes.

Question 19

Give examples of a RNA retrovirus

Answer 19

human immunodeficiency virus (HIV)

Question 20

Name DNA virus

Answer 20

y lambda phage

Question 21

name some RNA viruses

Answer 21

tobacco mosaic and Ebola

Question 22

how does cell lysis happen

Answer 22

in the lytic pathway the new phage particles are assembled as new protein coats are made around their DNA .

The enzyme lysozyme is synthesised and released

Question 23

Describe the differences between Positive ssRNA , Negative ssRNA and RNA retroviruses.

Answer 23

POSITIVE ssRNA- single strand of RNA that is a sense strand used directly as mRNA to for translation into proteins at ribosomes. Also include RNA polymerase which is used to replicate the viral RNA

NEGATIVE ssRNA- single strand of RNA which is antisense. Before it can be used to make viral proteins more viral RNA must be transcribed into a sense strand.

This imports RNA replicase which uses free bases in the host cell to transcribe the antisense RNA strand and produce sense strand that can be translated at the ribosomes.

RNA Retroviruses- Viral RNA that cannot be used as mRNA but is translated into DNA by reverse transcriptase in the cytoplasm of the cell. The viral DNA passes into the nucleus of the cell. The viral DNA passes into the nucleus of the host cell where it is inserted into the host DNA.

Host transcriptase–> viral mRNA ns new viral genome RNA. The new particles leave the cell by exocytosis.

Question 24

How do viruses cause disease by . . .

Answer 24

Lysis of the host -causes host cell to release its own lysomes and digest themselves from the inside or by the production of toxins that inhibit cell metabolism.