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BIO 435: Virology > Viral Structure and Genome Replication > Flashcards

Viral Structure and Genome Replication Flashcards

1
Q

What are the three main functions of the capsid and other virion proteins?

A

PPD

1) Protection of Genome
2) Packaging Genome properly
3) Delivery of Genome into new Host

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2
Q

What is a protein subunit?

A

single folded polypeptide chain

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3
Q

What is the structural unit of the virus?

A

A protomer, a unit from which capsids are built

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4
Q

What is the capsid?

A

Protein shell surrounding the nucleic acid genome of the virus

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5
Q

What is the nucleocapsid?

A

Nucleic Acid and Protein assembly that is packaged within the virion

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6
Q

What is the envelope?

A

Host-cell derived lipid bilayer carrying glycoproteins

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7
Q

What is the virion?

A

infectious virus particle

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8
Q

Each type of virus has a specific type of capsid. What are the types?

A
  1. Icosahedral - 20 sided “soccer ball”
    • Made up of multiple repeating virus proteins
  2. Helical - rolled up like newspaper
    • Flat planar net of protein subunits
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9
Q

What is significant about the “spikes” found on the membranous envelopes surrounding the capsids of some viruses?

A

These glycoproteins on the envelope bind to specific receptor molecules on the surface of a host cell

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10
Q

What is the viral genome?

A

Nucleic acid storage of information that’s needed to BUILD, REPLICATE, and TRANSMIT a virus

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11
Q

What are the types of Viral Genomes?

A

Either DNA or RNA Virus

  • ssDNA or dsDNA
  • ssRNA or dsRNA
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12
Q

What are the two types of RNA genome strand polarities?

A

Strand Type determines what the virus has to do in order to initiate replication and express viral genome

Positive (+) (5’ to 3’)

  • first step is translation = produce viral proteins
  • already 5’ to 3’ so it can go directly to ribosome

Negative (-) (3’ to 5’)

  • first step is transcription = make mRNA
  • makes positive sense mRNA which can now be used for translation
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13
Q

What must all viruses do early on in infection to ensure replication?

A

express their genes as functional mRNAs to direct the cell’s ribosomes to make viral proteins

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14
Q

How do dsDNA viruses create viral proteins?

A

1) Have to get into host cell nucleus
2) Host cell RNA Polymerase II binds to viral DNA genome and transcribes viral DNA genes into mRNA
3) mRNA is then read by host cell ribosomes which translates it into viral proteins

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15
Q

How do (+) RNA viruses produce viral proteins?

A
  1. Virus enters host cell
  2. Capsid disassembles (uncoats)
  3. Viral genome is (+) RNA so it acts as mRNA for translation
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16
Q

Cells don’t have the machinery to recognize an RNA template and make an RNA transcript. How do RNA Viruses get around this?

A

RNA-dependent RNA Polymerase (RDRP)

  • (-)RNA viruses have to physically carry the RDRP enzyme with them into the cell
  • (+)RNA code for RDRP but don’t have to carry an RDRP enzyme with them into the cell
17
Q

What kind of viruses have a high mutation rate? Why?

A

RNA viruses because RNA Polymerase has no proofreading ability

  • also have a higher error rate than DNA viruses
  • mutations occur frequently
18
Q

Walk through the process of Positive strand (+) RNA virus replication.

A
  1. Infection
  2. Virus uncoating
  3. Immediate production of viral proteins (including RDRP)
  4. RDRP binds to positive sense (+) genome and produces a complimentary negative sense (-) antigenome
  5. RDRP binds to antigenome and Positive (+) strand genomes generated
  6. These new genomes are packaged into pre-assembled capsids
19
Q

Walk through the process of Negative strand (-) RNA virus replication.

A
  1. Infection
  2. Uncoating
  3. RDRP (brought in with virus) binds to negative sense (-) genome and produces mRNA and complimentary positive (+) strand antigenome
  4. Production of viral proteins using mRNA produced by RDRP
  5. RDRP binds to antigenome and Negative (-) strand genomes generated
  6. Genomes packaged into pre-assembled capsids
20
Q

Walk through the process of dsDNA virus replication.

A
  1. Infection
  2. Uncoating
  3. Transcription to produce mRNAs and Replication to produce viral genomes
    • Most DNA viruses use host RNA polymerase for transcription
    • Some DNA viruses use host DNA polymerase for replication
    • Some DNA viruses encode their own DNA polymerase
  4. Viral Proteins made
  5. Generation of dsDNA genomes
  6. Genome packaged into pre-assembled capsids
21
Q

Walk through the process of RNA Genome Retrovirus replication.

A
  1. Infection w/ ssRNA genome
  2. Make ssDNA copy from RNA genome using Reverse Transcriptase (RT physically brought into host cell w/ virus)
    • RT also can be called RNA Dependent DNA Polymerase
  3. DNA replicated to make dsDNA
  4. DNA is integrated into the host genome
  5. Host polymerase generates mRNAs and viral genomes
  6. Genomes packaged into pre-assembled capsids

BIO 435: Virology (18 decks)

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