Introduction to Microbial World (Viruses)

Question 1

what is the life cycle of a virus?

Answer 1

1. attachment and entry
2. genome replication
3. production of proteins
4. assembly
5. release of new viruses

Question 2

define the term virus

Answer 2

a package of genetic information (DNA or RNA) protected by a protein shell for delivery into a host cell to be expressed and replicated

Question 3

what genetic code do viruses use?

Answer 3

DNA or RNA

Question 4

where are viral replication sites for viruses?

which type go where?

Answer 4

• *cytoplasm:** most RNA viruses
• *nucleus:** most DNA viruses

(some do both e.g. retroviruses)

Question 5

on av. how many known virus families are people infected by?

Answer 5

10

Question 6

how many viruses are known to infect humans?

(which human systems can be infected by viruses? )

Answer 6

>200 viruses

- human systems affected

• NS
• resp
• skin
• liver
• heart
• sexual
• pancreas
• GI
• Eyes

Question 7

what are the function of viral structural proteins?

Answer 7

• protect the genome
• recognise the viral nucleic acid for packaging
• deliver viral nucleic acid to host cells

Question 8

what are capsids?

what is nucleocapsid?

Answer 8

The capsid surrounds the virus and is composed of a finite number of protein subunits known as capsomeres, which usually associate with, or are found close to, the virion nucleic acid.

nucleocapsid: capsid protein + viral nucleic acid

Question 9

what are the three types of symmetry used to make viruses ? what does this mean the virus types are like?

what is ^ determined by?

Answer 9

depends on the capsid of the virus

1. helical symmetry

2. icosahedral symmetry (VP1, VP2 & VP3 are building blocks that make structure)

3. complex symmetry

t_herefore you get following virus structures:_

a) non-enveloped virus with a helical capsid
b) non-enveloped virus with a icosahedral capsid
c) enveloped virus with a helical capsid
d) enveloped virus with a icosahedral capsid

Question 11

where do virus capsids acquire the virus envelope from?

Answer 11

capsids acquire envelope from host cell:

• lipid envelopes are derived from cellular membranes
• studded with surface projections: e.g. spikes
• usually glycosylated by host systems prior: them sticky

Question 12

what are the structure of most viruses?

Answer 12

a) non-enveloped virus with a helical capsid
b) non-enveloped virus with a icosahedral capsid
c) enveloped virus with a helical capsid
d) enveloped virus with a icosahedral capsid

But: get some exceptions !

Question 13

name a virus that is an exceptions to the normal 4 structural categories of viruses?

Answer 13

poxvirus: complex symmetry

Question 15

what does information in viral genome make viruses do? (5)

Answer 15

• replication of viral genome
• assembly and packing of the genome
• regulation and timing of replication cycle
• modulation of host defences
• spread to other cells and host

Question 16

what are the unifying princples of a) viral structures b) viral replication?

Answer 16

a) viral structures: all viruses package their genomes inside a particles that mediates transmission of the viral genome from host to host
b) viral replication: the viral genome contains the info for initiating and completing an infectious cycle within a susceptible, permissve cell.

Question 17

how do u classify viruses? what used to be based on?

what do virus families end in?

(sort of ignore and focus on next slide)

Answer 17

virus classification starts with order, family, genus or species.
classification used to based on:
- shape
- size of genomes
- if usa DNA or RNAA
- single / double stranded
- host characterisitcs
- disease associated with
- place discovered

• families: *(-viridae)
• *

Question 18

what is viral taxonomy / classification based on?

Answer 18

• shape
• type and form of nucleic acid (RNA-DNA)
• enveloped or naked
• mode of replication
• organization and antigenic differences

have different virus orders, familes, genus and species (but some virus families arent assigned to an order)

Question 19

what is the baltimore classification system?

Answer 19

Baltimore classification (first defined in 1971) is a classification system that places viruses into one of seven groups depending on a combination of their nucleic acid (DNA or RNA), strandedness (single-stranded or double-stranded), Sense, and method of replication.

dsDNA viruses
ssDNA viruses
dsRNA viruses
(+)ssRNA viruses
(-)ssRNA viruses
ssRNA-RT viruses
dsDNA-RT viruses

Question 20

what are the different classifications for baltimore classificaiton system?

Answer 20

I: dsDNA viruses (e.g. Adenoviruses, Herpesviruses, Poxviruses)

II: ssDNA viruses (+)sense DNA (e.g. Parvoviruses)

III: dsRNA viruses (e.g. Reoviruses)

IV: (+)ssRNA viruses (+)sense RNA (e.g. Picornaviruses, Togaviruses)

V: (−)ssRNA viruses (−)sense RNA (e.g. Orthomyxoviruses, Rhabdoviruses)

VI: ssRNA-RT viruses (+)sense RNA with DNA intermediate in life-cycle (e.g. Retroviruses)

VII: dsDNA-RT viruses (e.g. Hepadnaviruses)

Question 21

what type of virus (from baltimore classification) is:

• coronavirus
• influenza
• HIV?

Answer 21

• coronavirus: (+)ssRNA viruses
• influenza:(-)ssRNA viruses
• HIV: ssRNA-RT viruses

Question 22

Role of:

Reverse transcriptase ?

Integrase ?

Protease ?

RNA polymerase ?

Answer 22

Reverse transcriptase – turns +ssRNA into DNA

Integrase – integrates viral DNA with host genome

Protease – help create viral building blocks

RNA polymerase – forms mRNA before going to ribosome