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Mirobiology > Viruses > Flashcards

Viruses Flashcards

0
Q

Why are some viruses harmful?

A

Invade cell, viruses force cell to make copy of virus, so many copies made , cell explodes releasing all of the new viruses.

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1
Q

What is a virus?

A

It’s either DNA or RNA that is protected by a protein coat called a capsid (non living). Need a host

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2
Q

Who do viruses infect?

A

Bacteria - bacteriophage
Plants- eg. Tabacco mosaic virus
Animals- common cold

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3
Q

List the properties of a virus?

A 
Obligate parasite
Must have a host to exist
Have either dna or RNA but not both
Viruses direct synthesis of new virus within a host cell
Newly made viruses infect other cell
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4
Q

How do viruses differ from a living cell?

A

Simple a cellular organisation.
Presence of DNA or RNA but not both
Can’t reproduce independently or carry out cell division

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5
Q

What size are viruses?

A

Smallest infectious agents (have to fit into other cells)
Only seen with electron micro
Provirus 20 nm in diameter.

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6
Q

Name the structure of a virus?

A 
Neuclocapsid
Capsid 
Some have envelopes or tail
Envelope = enveloped virus 
Non envelope = naked virus
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7
Q

What is the capsid made of?

A

Protein subunits called capsomers.

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8
Q

Name the 2 types of capsid?

A

Helical (rod shaped) eg. Tabacco mosaic virus
Icosahderal ( 3d, 20 sided figure, 12 evenly spaced corners)
Eg. Adenovirus 90-100nm, non enveloped, dsDna - one of natures favourite shapes very efficient.

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9
Q

What is a virus envelope made off?

A

It’s a bit of the hosts cell membrane in the form of an envelope formed during replication or release.
Made of lipid bilayer
Glycoproteins (spikes) essential for attachment.

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10
Q

Give an example of an enveloped virus?

A

Herpes simplex

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11
Q

How are viruses classified?

A

Shape (helical, polyhedral,spherical,complex)
Genetic material (dsDna, ssDna, dsRna, ssRna)
Presence or absence of an envelope

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12
Q

List the characteristics of a ssDNA virus?

A 
Small genome 2-7kb
Circular genomes
No envelope
Mostly icosahedral capsid
Eg. Parvovirus and slap cheek
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13
Q

List the characteristics of a dsDNA?

A

One of the largest known viruses (genome 5-180 kb linear and circular)
No dsDNA virus is known to infect plants
Phages are dsDNA viruses 95%
Eg. Herpes simplex, hover viral meningitis.

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14
Q

List the characteristics of dsRNA?

A

Icosahedral capsids that stay intact inside the cell provide protection
Transcription occurs via viral rna, just use host cell machinery
Capable of infecting multiple species
Eg rotavirus ( gastroenteritis )

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15
Q

List the characteristics of ssRna virus?

A

This group includes some of the deadliest
Helical neucleocapsids
Coronavirus has largest genome of ssRna
Eg. Ebola, rabies,measles

16
Q

List the 5 stages involved in the reproduction of a retrovirus ?

A
  1. Building and entry(arrives at host with reverse transcriptase
  2. Reverse transcription occurs
  3. Integration- viral dna enters nucleus (can lie dormant)
  4. transcripion and translation- build up proteins with viral rna
  5. Viruses assembled and released.
17
Q

How does a virus infect its host?

A

They are specfic (glycoproteins act as flags which correspond to those on the surface of the host cells)
May be so specfic that they infect a particular type of cell eg. HIV only attacks t lymphocytes

18
Q

List the stages of the lytic cycle?

A 
Attachment
Entry and degradation of hosts dna
Synthesis of new viruses.
Assembly of parts into new viruses
Release of new viruses
19
Q

Give examples of lytic viruses?

A

SARS, common cold, flu, rabies, AIDS, Tabacco mosaic

20
Q

What is the lysogenic stage?

A

Known as latent infections
Virus inserts it’s genetic material into host chromosome.
Lies dormant and virus dna carried on by daughter cells after cell division

21
Q

What is the lytic stage?

A

Virus immediately replicates after infecting the host and the bursts out of the host cell, killing it.

22
Q

Name some lysogenic viruses?

A

HIV
Herpes
Hep b
Chicken pox varicella zoster

23
Q

List the stages of the lysogenic life cycle?

A

Attachment
Entry but no degradation of host dna
Integration into host dna
Mitosis-host and virus dna duplicated then cytokinesis

24
Q

How many viruses can a virus produce before host cell bursts ?

A

Up to 200

25
Q

List the infection cycle in humans?

A

Absorption, penetration, uncoating, synthesis, assembly and release.

26
Q

How can viral disease be prevented?

A

Good hygiene.

Avoid contact with contaminated food,water,faeces,body fluids.

27
Q

How can viral disease be prevented?

A

Vaccine- not available for all viruses

Anti viral drugs

28
Q

How can viruses be helpful?

A

Help cure genetic disorders- gene therapy

Mirobiology (8 decks)

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