Viral properties

Question 1

What is the size of viruses?

Answer 1

20 to 120 nm, smaller than bacteria.

Question 2

What are the characteristic features of viruses?

Answer 2

Obligate intracellular pathogens which have a DNA or RNA genome. They have no cyptoplasm or nucleus and are not considered cells.

Question 3

What is the shape of viruses?

Answer 3

Spherical, filamentous or icosahedral.

Question 4

What is an icosahedral virus?

Answer 4

Geometric shape with 20 sides of equilateral triangles, increasing number of structural units to increase the size of the capsid. Each face has proteins which can self-assemble.

Question 5

How do viruses replicate?

Answer 5

They are obligate intracellular pathogens which hijack the cell genome to interfere with transcription/translational self-assemble individual viral components such as nucleic acids and a capsid

Question 6

What is the genome of a virus?

Answer 6

Viral genetic material within a nucleocapsid in the form of DNA or RNA. Capsid is formed of individual subunits of capsomers.

Question 7

What is a virion?

Answer 7

Extracelullular Infective form of a virus outside the host cell. It has a DNA/RNA core surrounded by capsid. It is only infectious if fully assemlbled.

Question 8

What is an enveloped virus?

Answer 8

Contains a lipid-protein bilayer for protection of viral genome formed from the host cell membrane. It contains cell surface glycoprotein spikes for virus-cell fusion.

Question 9

How does the capsid form?

Answer 9

Structural proteins self assemble

Question 10

What is a naked virus?

Answer 10

Does not have an envelope and more stable in response to environmental stress such as acidity and temperature. It spreads more easily and survives gut and poor water treatment

Question 11

What are the requirements of enveloped viruses?

Answer 11

More sensitive to environmental stressors. Must stay wet to remain infectious and spreads through large droplets. It does not need to kill cell to spread and membrane is sensitive to detergents.

Question 12

What is the influenza virus?

Answer 12

Spherical enveloped virus which contains a H (haemogluttin) spike and a N (neuroaminidase) spike. These are susceptible to antigenic shift and recombination

Question 13

How does the influenza virus initiate infection?

Answer 13

Contains H spike haemogluttin receptor which binds to sialic acid on glycolipid/glycoprotein on respiratory epithelia surface

Question 14

How does the influenza virus leave the host cell?

Answer 14

The N spike on the influenza virus contains the enzyme neuroaminidase which cleaves sialic acid to cause release of the virus.

Question 15

What is norovirus?

Answer 15

Icosahedral virus with an RNA genome spread through contaminated surfaces or via people.

Question 16

What is the viral genome?

Answer 16

Contained inside a capsid of either single/double stranded DNA or RNA which is linear/circular. it codes for all proteins not produced by the target host cell. The genome is delivered to the host cell to produce proteins via transcription + translation.

Question 17

What does the viral genome encode for?

Answer 17

Proteins to produce the progeny viral particle such as virions
Proteins to attack host defences
Enzymes for genome replication

Question 18

How are viral genomes classified?

Answer 18

Strategy of nucleic acid and identity/polarity of nucleic acid

Question 19

How do viruses produce new viral proteins?

Answer 19

THey produce viral mRNA which undergoes translation. Negative strand RNA require viral proteins for this process but positive strand immediately enters translation. This occurs in the cyptoplasm.

Question 20

How do viruses produce nucleic acids?

Answer 20

Make copies of the genome

Question 21

Stages of viral infection cycle

Answer 21

Attachment, penetration, uncoating, new genome/protein synthesis, assembly of new particles and release

Question 22

What is a DNA virus?

Answer 22

Genome with either single stranded DNA or double stranded DNA.

Question 23

What is an RNA virus?

Answer 23

Genome with single stranded RNA
Double stranded RNA

Question 24

What do RNA viruses synthesise in host cell?

Answer 24

RNA genome, copy of genome and mRNA.

Question 25

What is RNA +/ positive strand RNA?

Answer 25

RNA which has a genome that also exists as a single stranded mRNA and upon entry into host cell cyptoplasm, immediately undergoes translation to produce capsid proteins, replicate mRNA or progeny viruses release for budding

Question 26

Which viruses are + positive strand RNA?

Answer 26

Hepatitis A, Hep C, Hep E
Rubella
Poliovirus, COVID-19

Question 27

What is RNA -/negative strand RNA?

Answer 27

All are enveloped viruses which requires enzymes on the capsid for mRNA synthesis. It must be converted into positive sense RNA by RNA polymerase in viral transcription + translation to produce viral proteins for capsid or progeny viral proteins to be released by budding.

Question 28

Which viruses are - negative strand RNA?

Answer 28

Rabies, measles, mumps, influenza, ebola

Question 29

What is reverse transcriptase?

Answer 29

DNA polymerase enzyme used by viruses to transcribe single stranded RNA into DNA.

Question 30

Which viruses use reverse transcriptase?

Answer 30

Retrovirus such as HIV
Double stranded DNA Hepadna (Hep B) virus which uses an RNA intermediate

Question 31

How does an enveloped virus enter host cell

Answer 31

Enveloped viruses attach to host cell membrane and form endosome containing nucleocapsid or via fusion.
Cell membrane participates in viral attachment via receptors

Question 32

What is the alternative route to endocytosis?

Answer 32

Fusion- Virus attaches to receptor and uses with host cell membrane via envelope and releases nucleocapsid which travels along cytoskeletal filaments

Question 33

How does the endosome travel to cyptoplasm?

Answer 33

Adaptor proteins attach at the cell membrane to the endosome, allowing association by clarithrin to form a clarithrin coat for uptake

Question 34

What is the rabies virus?

Answer 34

Negative strand RNA virus which enters host cell via endocytosis and uses polymerases and capsid proteins for transcription and translation

Question 35

What is hepatitis B?

Answer 35

Double stranded DNA virus which is blood borne and causes liver disease. It is transmitted via exposure to contaminated blood.

Uses reverse transcription to replicate and causes chronic infection which can cause liver cancer.

Question 36

What is burst size?

Answer 36

Yield of infectious virus produced from an infected cell

Question 37

HIV

Answer 37

Retrovirus which replicates using the virion enzyme reverse transcriptase

Question 38

How do DNA viruses replicate?

Answer 38

Immediate early genes are transcribed and translated to form polymerase enzymes for replication of viral DNA. Late genes are then transcribed into mRNA and translated to produce the capsids and progenors.

Question 39

Why are viral infections so prominent?

Answer 39

Drug resistance, few drugs are available. Viral resistance can occur. There is a high mutagenic rate of the viral polymerase and recombination

Question 40

What is the effect of viral infection on the host cell?

Answer 40

Cell lysis, Latency before lysis, persistent infection with slow release of virus without lysis, cause transformation of host cell into tumour cell

Question 41

Why does host cell transformation to tumour cell occur?

Answer 41

Due to insertion of viral DNA into genome