Unit 2- Viruses Flashcards

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1
Q

What 3 components make up a virus?

A
  • nucleic acid
  • a protein coat
  • a lipid envelope
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2
Q

Do Viruses have RNA or DNA?

A

Viruses can have double and single strands of RNA or DNA

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3
Q

Describe the structure of a protein coat:

A
  • it is also called a capsid
  • made of subunit capsomeres
  • simple geometrical shapes such as helix or icosahedrons
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4
Q

How does the lipid protein stay attached to the capsid? And where does the lipid envelope come from?

A
  • the lipid envelope is derived from a host cell membrane, so the virus doesn’t make it
  • the lipid envelope contains matrix proteins that link to glycoproteins in the capsid
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5
Q

What is a virus particle outside of a cell called?

A

A vision

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6
Q

Name the kind of nucleic acid the following bacteria have: Lambda phage, TMV, Ebola, HIV

A

Lambda phage- ds DNA
TMV- ss RNA (+ve sense strand)
Ebola- ss RNA (-ve sense strand)
HIV- ss RNA (retrovirus)

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7
Q

Structure of a lambda phage:

A
  • icosahedral head containing ds DNA
  • helical sheath
  • base plate
  • tails
  • considered complex
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8
Q

Structure of the TMV:

A
  • coil of single stranded RNA
  • surrounded by a helical capsid
  • very small
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9
Q

Structure of Ebola virus:

A
  • very large
  • negative sense single strand RNA
  • surrounded by a large flexible helical capsid
  • enclosed in a lipid envelope
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10
Q

Structure of HIV:

A
  • Single stranded RNA
  • surrounded by icosahedral capsid
  • surrounded by a sphere of proteins attached to a lipid envelope
  • contains the enzyme reverse transcriptase
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11
Q

How do we classify viruses?

A

By type of nucleic acid

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12
Q

Summary of how a virus infects a host cell:

A
  • virus nucleic acid in injected into host cell
  • capsid remains outside the cell
  • the host cells ribosomes, enzymes, nucleotides, amino acids etc are used to synthesise new viral nucleic acid and proteins
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13
Q

What is meant by a positive sense strand?

A

It can be directly translated into the proteins

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14
Q

How does TMV replicate?

A
  • TMV infects plant cells through damaged cell walls and contains positive sense RNA into the host
  • the viral RNA is uncoated
  • the RNA sequence can be translated directly by ribosomes to synthesise viral proteins
  • the virus particles can also spread through the plant via plasmodesmata
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15
Q

How does phage lambda replicate?

A
  • Lambda phage attaches to host cell and injects its DNA into host cell cytoplasm
  • the viral DNA is integrated into hosts bacterium DNA becoming a PROPHAGE
  • prophage means bacterial DNA with viral DNA (like a vector)
  • prophage remains latent and is replicated every time the host cell divides
  • that was the lysogenic phase
  • due to an environmental signal the viral DNA starts being expressed into phage proteins which assemble into phage capsid
  • the cell bursts by lysis
  • this is the lytic phase
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16
Q

How does Ebola replicate:

A
  • the virus attaches to the host cell, the 2 membranes fuse, releasing capsid into cell cytoplasm
  • the viral RNA is uncoated and the viral enzyme RNA polymerase synthesises many copies of mRNA from the negative sense viral RNA, using the host cell nucleotides
  • the mRNA is translated to make viral proteins which assemble into virus capsids
  • the virus particles are released by budding, collecting their lipid envelope from the cell membrane
17
Q

How is HIV replicated?

A
  • the virus attaches to host cell and the 2 membranes fuse, releasing the capsid into the membrane
  • the viral enzyme reverse transcriptase synthesises double stranded DNA from the single stranded RNA
  • the DNA is incorporated into the hosts DNA, this is called provirus
  • the provirus remains latent for years and is replicated every time the cell divides
  • an environmental trigger causes the viral DNA to express viral proteins which assemble into a viral capsid
  • the virus particles are released by budding, using the cell membrane to make their lipid envelope