CSIM 1.14 Case 40 Launch A Spotty Problem The Biology of Viruses Flashcards

1
Q

What is a virus?

A

A SUBmicroscopic entity consisting of a single nucleic acid surrounded by a protein coat capable of replication only within host cells

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2
Q

What does submicroscopic mean?

A

Cannot be seen down a microscope

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3
Q

Describe how the genetic material of viruses can vary

A
  • RNA or DNA
    • Single or double stranded
    • One molecule or segmented
    • Few to hundreds of proteins coded
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4
Q

Recall the types of proteins coded for by viruses

A

Structural proteins
• Capsid proteins
• Surface spikes

Non structural proteins
• Enzymes
• Block host immune system

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5
Q

What is the most common structure/shape for viral capsids?

A

Icosohedron

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6
Q

What is the function of:

1) Capsids?
2) Surface spikes?

A

1) Protects the DNA/RNA from degradation

2) Allows attachment to cells

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7
Q

What is the difference between capsids and envelopes?

A

Envelopes are made of lipids and are acquired from cell membranes during exocytosis

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8
Q

What is the function of lipid envelopes

A

Contains viral proteins which are required for the virus to attach to and infect a new cell

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9
Q

Which viruses have surface spikes?

A

All those without a lipid envelops (as these act as replacements for the viral proteins in the lipid bilayer)

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10
Q

Name the surface proteins found on viruses

A
  • Haemagglutinin
    • Neuraminidase

(where H1N1, etc. comes from)

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11
Q

What are viruses classified by?

A
  • Nucleic acid
    • Replication strategy
    • Similarity of nucleic acid sequence
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12
Q

Describe the Baltimore classification of viruses

A
  • Single stranded DNA
    • Double stranded DNA
    • Positive sense single stranded RNA
    • Negative sense (antisense) single stranded RNA
    • Single stranded RNA viruses which use reverse transcription (RETROVIRUSES)
    • Double stranded RNA
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13
Q

How are viruses grouped together in the baltimore system further classified?

A

• Classified into families based on nucleic acid sequence

• Within families, classified into genotype and serotype:
> Genotype based on genome organisation and sequence differences
> Serotype based on reactivity to antibodies

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14
Q

How do double-stranded DNA viruses replicate?

A
  • Replicates DNA and transcribes a positive sense mRNA strand (for the proteins) in exactly the same way human cells do.
    • Uses viral DNA polymerase for DNA replication, but hijacks cellular machinery for protein synthesis

IMG 37

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15
Q

What are the three main families of double stranded DNA viruses?

A
  • Papovaviridae
    • Adenoviridae
    • Herpesveridae
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16
Q

How do negative sense (antisense) single stranded RNA viruses replicate?

A
  • Makes a positive sense mRNA molecule, using the viral antisense RNA as a template
    • The mRNA is used to transcribe viral proteins
    • The mRNA is also used as a template to create more antisense viral RNA for the progeny virus

IMG 38

17
Q

What are two main families of negative sense single stranded RNA viruses? Give examples of these

A
Orthomyxoviridae
  •  Infuenza
Paramyxoviridae
  •  Measles
  •  Mumps
18
Q

How do positive sense single stranded RNA viruses replicate?

A
  • The viral RNA is used as mRNA directly for translation of a polyprotein, which is cleaved by viral or host enzymes
    • To replicate, the viral RNA makes an antisense intermediate, which is then used as a template to make more positive sense RNA for the progeny virus

IMG 39

19
Q

What are two main families of positive sense single stranded RNA viruses? Give examples of these

A

Picornaviridae
• Rhinovirus
• Hepatitis A
• Poliovirus

Hepaciviridae
• Hepatitis C

20
Q

What is the main family of single stranded DNA viruses? Give an example

A

Parvoviridae

• Parvovirus

21
Q

What is the main family of double stranded RNA viruses? Give an example

A

Rotaviridae

• Rotavirus

22
Q

Which Baltimore virus class integrates its genetic information into the human genome? Describe how these replicate

A

Retroviruses

  • Viral (sense) RNA is acted upon by reverse transcriptase to build a double-stranded DNA copy
  • This DNA is integrated into the genome of the host cell
  • From there, the DNA creates (sense) mRNA (NB: remember transcription uses antisense strand as a template)
  • This sense mRNA is used to make the viral polyproteins, and some of it is preserved to be packaged into the virus (remember we started with sense RNA)
23
Q

Which viruses create polyproteins

A

All RNA viruses which begin with a ‘sense’ strand:
• Retroviruses
• Positive sense single stranded RNA viruses

24
Q

What are the stages of the viral life cycle which may be targeted by antiviral therapies?

A

1) attachment
2) entry
3) replication
4) integration
5) protein synthesis
6) assembly
7) release

25
Which viral DNA polymerase inhibitor acts against herpes simplex virus?
Aciclovir
26
Give examples of retrovirus
HIV | HTLV (human T-lymphocyte virus)