Middleton - Virus Classification, structure & Replication

Question 1

What attributes classify viruses?

Answer 1

• Virus particle structure
• Genome
• Replication
• Serology
• Stability

Question 2

Virus is defined by the presence of a ________.

Answer 2

Nucleocapsid structure

Question 3

What are the 3 types of structure the nucleocapsid can assume?

Answer 3

• helical
• pleomorphic
• Icosahedral

Question 4

Nucleocapsid is comprised of repeating protein subunits called __________.

Answer 4

Capsomeres

Question 5

________ are virus modified cellular membranes acquired upon exit from host.

Answer 5

Envelopes

Question 6

Size range of a virus?

Answer 6

18nm-300nm

Question 7

Enveloped viruses may have nucleocapsids with _____________.

Answer 7

Different structures

Question 8

What kinds of RNA are in the viral genome?

Answer 8

• Double stranded

- Single stranded (+sense, -Sense & ambisense)

Question 9

Central dogma

Answer 9

info flows from DNA downward.

Question 10

What types of structures are found in the viral genome?

Answer 10

• Linear
• circular
• segmented
• diploid

Question 11

What is needed to get replication started in viruses?

Answer 11

hairpin

Question 12

What are the steps of Virus Replication?

Answer 12

• Attachment
• Entry
• Transcription
• Translation
• Replication
• Assembly
• release

Question 13

What two components are needed for attachment?

Answer 13

Cellular receptors

• signaling molecules
• cell adhesion
• transport

Viral Transporters

• Usually do not mimic cell receptor’s normal ligand
• Typically spike-like projections on particle surface
• May require a co-receptor

Question 14

__________ can change receptor recognition.

Answer 14

Genetic engineering

• Integrin RGD sequence = used by Ad, engineered into lambdaphage.
• Pseudotyping particles = improve retroviral entry (VSV, Ebola & LCMV)

Question 15

_______ ia a major determinant of virus tropism (Host range or hosts that virus will infect)

Answer 15

Attachment

Question 16

Viruses can infect essentially all forms of life, but where do they draw the line in infection?

Answer 16

They don’t cross kingdoms or across more divergent hosts (Plants —> people)

Question 17

________ is a major factor in eradication of a virus.

Answer 17

Host range

Question 18

What are the 2 pathways of entry for a virus?

Answer 18

• Receptor mediated endocytosis
• Direct penetration of plasma membrane
• methods of non enveloped viruses are not well understood (uses pores called picornavirus)

Question 19

How does entry work with a enveloped virus?

Answer 19

1. Membrane fusion
2. Receptor Conformational change (low pH)
3. Uncoating
   - Nuclear Replication = Genome and remaining protein coat transported to the nuclear membrane
   - Cytoplasmic Replication = Release of genome into cytoplasm & Transportation of the genome into intracellular site of replication. *dsRNA viruses NEVER release their genomic material from the entering particle.

Question 20

What are the steps of virus Transcription?

Answer 20

1) Production of messenger RNA (mRNA) template for protein synthesis.
* THE GENOME OF (+) ssRNA can serve as mRNA!
* Production of new transcripts can occur later using (-) ssRNA.

Question 21

DNA viruses usually rely on ___________ during Transcription

Answer 21

Cellular RNA polymerases

Question 22

_________ & _________ viruses must bring their own polymerases into the cell during Transcription.

Answer 22

(-) ssRNA & dsRNA

Question 23

True or false - during translation, all viruses need the cell’s ribosomes to produce protein?

Answer 23

True - no exceptions!

Question 24

Where can viral protein production be regulated?

Answer 24

at the Transcript (mRNA) level or translation level

Question 25

During translation Structural proteins are found in _______ quantities.

Answer 25

High

Question 26

Durin translation, ____________ are only seen inside the infected cell.

Answer 26

Non-structural proteins

Question 27

What is the order of events in Genome Replication?

Answer 27

Hah! The order of events depends of the virus genome!

Question 28

What is unique to Genome Replication with (+)ssRNA?

Answer 28

- Genome serves as template for translation | - Polymerase makes (-)ssRNA copy as template for new genomes.

Question 29

What is unique to Genome Replication with (-)ssRNA?

Answer 29

- Virus particles must include the viral polymers - Polymerase makes messenger RNA for translation - Genome replicates through full-length (+)ssRNA intermediate.

Question 30

What is unique to Genome replication with dsRNA?

Answer 30

- Virus particle includes viral polymerase - dsRNA induces innate immune response so genome stays inside particle. - mRNA synthesized in particle and exported to cytoplasm - mRNA serves as (+) strand in virus genome, (-) strand synthesized during assembly.

Question 31

What is unique to Genome replication with ssDNA & dsDNA?

Answer 31

- Must gain access to nucleus! * Poxviruses are the exceptions - Prepare the cell for DNA replication - Ensure genome ends are copied