1:Structure/Classification/Pathogenesis

Question 1

Four characteristics of Viruses:

Answer 1

1. Nucleic acid genome packaged in a protein coat. Protein for protection and genome for initiation and completion of infectious cycle.
2. Unable to generate energy or synthesise proteins. Must make mRNA that can be translated by host ribosomes.
3. Replication, not growth or division.
4. Enter hosts via cellular receptors.

Question 2

Where do viruses function?

Answer 2

They are obligate intracellular parasites, meaning their genome can only function within a living cell.

Question 3

Functions of the nucleocapsid?

Answer 3

Protecting the viral genome, transmission and infection.

Question 4

Characteristics of icosahedral nucleocapsids:

Answer 4

Package DNA or RNA, released by lysis (non-enveloped), or by budding (enveloped viruses).

Question 5

Characteristics of helical nucleocapsids:.

Answer 5

Protein subunits wrapped around genome, usually packaging RNA, usually enveloped and associated with matrix protein.

Question 6

Immunogenic components of viruses?

Answer 6

The envelope, if present, or the nucleocapsid. They are immunogenic because they contain antigenic epitopes.

Question 7

Method of envelope budding

Answer 7

Expression of viral proteins cell membrane, nucleocapsid buds through membrane, forming the envelope.

Question 8

Pros/Cons of an envelope

Answer 8

Pros: Surrounds the nucleocapsid, aids in transmission and infection.
Cons: Confers instability, may be easily dehydrated.

Question 9

3 Methods envelopes develop:

Answer 9

1. Budding from the plasma membrane
2. Bud into cytoplasmic vesicles, released by exocytosis.
3. Budding through the nuclear membrane.

Question 10

Location of viral matrix protein

Answer 10

Located between the the envelope and the nucleocapsid in viruses that bud from the plasma membrane.

Question 11

Location of tegument protein

Answer 11

Between NC and envelope in viruses that bud from the nuclear membrane.

Question 12

Characteristics of Virus genomes

Answer 12

RNA or DNA
Single or Double stranded
Segmented, linear or circular.
Contains open reading frames.

Question 13

Functions of viral genome

Answer 13

Acts as mRNA or template for mRNA.

Template to produce new progeny genomes.

Question 14

Viral enzymes are…

Answer 14

…contained within the NC, composed of protein and present in the virion only if they are needed prior to mRNA production.

Question 15

Functions of viral enzymes in the NC

Answer 15

Polymerase: Makes new genomes or mRNA
Integrase: Integrates HIV DNA into chromosome.
Protease: Digests virus polyproteins.

Question 16

Picornaviridae

Answer 16

+ve ss RNA, icosahedral naked NC, cytophatic (NC released by lysis).
e.g. Poliovirus

Question 17

Hepadnaviridae

Answer 17

ds DNA, icosahedral NC, enveloped.

e.g. Hepatitis B virus

Question 18

Flaviviridae

Answer 18

+ve ssRNA, icosahedral NC, enveloped, released by budding in ER->Exocytosis.
e.g. Hepatitis C virus

Question 19

Retroviridae

Answer 19

+ve ssRNA, 2 gene copies, icosahedral NC, Matrix, enveloped.

e.g. HIV

Question 20

Orthomyxoviridae

Answer 20

• ve ssRNA, segmented genome, helical NC, Matrix, enveloped, released by budding from plasma membrane.
  e. g. Influenza A virus

Question 21

Herpesviridae

Answer 21

ds DNA genome, icosahedral NC, tegument proteins, enveloped, buds through nucleus.
e.g. Herpes simplex virus, varicella Zoster Virus.

Question 22

Stage 1 of viral pathogenesis:

Answer 22

1. Attachment
2. Penetration
3. Uncoating

Question 23

Stage 2 of viral pathogenesis

Answer 23

4. Gene expression

5. Gene replication

Question 24

Stage 3 of viral pathogenesis

Answer 24

6. Assembly of nucleocapsid
7. Packaging of genome and proteins
8. Release from cell

Question 25

3 methods of viral entry to cells

Answer 25

Receptor mediated endocytosis,

Surface fusion and direct injection (naked viruses)

Question 26

Start of open reading frame?

Answer 26

5’AUG codon

Question 27

End of open reading frame?

Answer 27

3’UAG codon

Question 28

3 coding strategies of genomes

Answer 28

1genome1ORF1Protein
1genome1ORF1+Proteins
1genome1+ORFs1+Proteins

Question 29

Enzymes carried in Poliovirus?

Answer 29

None! RdelRpol created later for replication

Question 30

Method of Hep C release?

Answer 30

Budding into ER

Question 31

Method of Hep B gene expression?

Answer 31

DNA from virus genome is converted from relaxed circular to cccDNA, mRNA is produced which codes for proteins and is then reverse transcribed to produce new genomic DNA

Question 32

Genome of Hep B?

Answer 32

Relaxed circular (+/-) ss DNA, with 4 open reading frames each coding for multiple proteins

Question 33

Enzymes contained in HIV?

Answer 33

Reverse transcriptase, integrase, protease.

Question 34

HIV envelope proteins and human receptor?

Answer 34

gp120 + gp41 bind to CD4 on T lymphocytes

Question 35

Genome of Influenza A?

Answer 35

8 randomly packaged linear segments each containing one ORF and coding for one protein

Question 36

Influenza A proteins and human receptors?

Answer 36

Haemaglutanin and neurominidase bind to sialic acid (N cleaves s. acid)

Question 37

Transport of herpes virus from ECF to nucleus

Answer 37

Enters via surface fusion, travels via dynein to nucleus, Genome (+/-dsDNA) enters though nuclear pore

Question 38

Transport of Herpes from Nucleus to ECF

Answer 38

Buds through inner nuclear membrane, viral proteins are expressed, buds through outer nuclear membrane into cytoplasm (loses envelope), re-enveloped in the ER and released via exocytosis