Virology

Question 1

How are viruses classified?

Answer 1

1. Morphology
2. Genome
3. Proteins
4. Genome organization and replication strategy
5. Antigenic properties
6. Biological properties

Question 2

What are the 3 common characteristics in all viruses?

Answer 2

1. Nucleic acid genome (DNA or RNA)
2. Capsid that protects the genome
3. Genome+capsid= nucleocapsid

Question 3

Describe a protein capsid

Answer 3

Usually a helix or iscosahedron.

Question 4

Describe a viral envelope

Answer 4

Composed of a lipid bilayer made from budding host CM. Contains viral proteins

Question 5

What are the non-structural proteins in Virions?

Answer 5

Nucleic acid binding proteins, replicases, transcription factors

Question 6

What is the eclipse period in a Lytic Viral growth curve?

Answer 6

The time until newly assembled virus appears in the cell

Question 7

What is the latent period in a lytic viral growth curve?

Answer 7

The time until new infectious virus appears in the medium.

Question 8

What are the steps in the viral life cycle?

Answer 8

Attachment, Entry, Uncoating, Targeting, Gene Expression, Genome replication, Virion Assembly, Release

Question 9

Discuss Viral attachment to the host cell.

Answer 9

Interaction between viral attachment protein and cell surface receptor. VAP is on surface of virus. CSRs are usually glycoproteins/lipids

Question 10

Relate tropism to viral attachment

Answer 10

Specific interaction between VAPs and CSRs is a determinant of tropism of virus.

Question 11

Discuss the penetration phase

Answer 11

Receptor mediated endocytosis or Direct entry at cell surface. The acidic environment of endosome causes the viral protein to change and mediates release of virion into cell; Fusion protein for enveloped viruses.

Question 12

What are the 6 classes of viral genomes?

Answer 12

1. Dsdna
2. Ssdna
3. DsRna
4. Positive strand Rna
5. Negative strand Rna
6. Retroviruses

Question 13

What is the scheme for Gene Expression/Replication for DNA viruses?

Answer 13

1. Expression of early genes.
2. Viral DNA replication
3. Expression of late genes which encode structural proteins.
4. Assembly of new virus particles and release.

Question 14

Discuss Parvoviruses

Answer 14

Contain ssDNA which is converted to dsDNA before it can be transcribed

Question 15

Discuss Poxviruses

Answer 15

Replicate in the cytoplasm; Must encode proteins needed for their own gene expression and replication.

Question 16

Describe RNA genome replication

Answer 16

RNA viruses must encode their own RNA replicases because cells don’t have RNA dependent RNA polymerases; High mutation rate

Question 17

Discuss + strand RNA viruses

Answer 17

+ strand indicates encapsidated genome can serve as mRNA and be directly translated into proteins; Infectious

Question 18

Explain + strand viral replication

Answer 18

Viral replicase synthesizes complementary - strand from + strand. The - strand is now a template to make + strands

Question 19

What are the 3 things the newly synthesized + strands used for

Answer 19

1. Produce viral proteins
2. Produce - strands
3. Packaged into virions

Question 20

Discuss - strand RNA viruses

Answer 20

Their genome can’t be used as a template for protein synthesis. These viruses must bring a viral replicase in with it.

Question 21

Explain - strand viral replication

Answer 21

• strands are used as a template to make + strands using a replicase. + strands (mRNAs) are translated to make viral proteins.

Question 22

Explain the replication strategy for retroviruses

Answer 22

Viral RNA is reverse transcribed into DNA using reverse transcriptase. RNA strand is digested and replaced with DNA making dsDNA.

Question 23

Distinguish the release of Non-enveloped viruses from Enveloped viruses

Answer 23

Non-Enveloped Viruses: Newly formed virions are released by cell lysis
Enveloped Viruses: Nucleocapsids assemble on CM and budd out.