viruses 2 -

Question 1

Parvovirus

Answer 1

requires cells underdoing DNA synthesis to replicate

Question 2

Papovavirus

Answer 2

stimulates cell growth and DNA synthesis

Question 3

Hepadnavirus

Answer 3

stimulates cell growth cell makes RNA intermediate ,encodes a reverse transcriptase

Question 4

Adenovirus

Answer 4

stimulates cellular DNA synthesis and encodes its own polymerase

Question 5

Herpesvirus

Answer 5

stimulates cell growth ,encodes its own polymerase and enzymes to provide deoxyribonucleotides for DNA synthesis ,establishes latent infection in host

Question 6

Poxvirus

Answer 6

encodes its own polymerases and enzymes to provide deoxyribonucleotides for DNA synthesis replication replication machinery and transcription machinery in the cytoplasm

Question 7

Group 1 -

Answer 7

• e.g herpesvirus
• non -enveloped or enveloped
• double stranded DNA genome
• replicate in the nucleus (*poxvirus)

Question 8

Early proteins in group 1

Answer 8

Target genome replication : like viral DNA polymerase

Question 9

Late proteins in group 1

Answer 9

• Parvovirus
• structural
• translocation back into the nucleus to form a capsid

Question 10

Group II

Answer 10

• non enveloped
• +/- sense single stranded DNA genome
• replicate in the nucleus
• ssDNA is converted to dsDNA by host factors and DNA polymerases
• ssDNA viruses produce virions containing either +/- DNA genome

Question 11

Group III

Answer 11

• Rotavirus
• virus entry leads to loss in VP4 and VP7
• triple layered particle goes into double layered particle
• DLP synthesizes each of the 11 mRNAs
• merase complexes replicate viral genome and generate each of the 11 genomic dsRNA segments.
• 11 genomic dsRNA segments into mature core results in formation of DLP.
• DLP acquires VP4 and VP7 and forms TLP which is released.

Question 12

Group IV -Poliovirus

Answer 12

• non-enveloped or enveloped
• +ve sense ,ssRNA
• replication occurs in the cytoplasm
• The (+ve) sense, ssRNA genome does not have a CAP but contains an IRES element
• The (+ve) sense, ssRNA is translated as a single polyprotein which is proteolytically cleaved into several polypeptides, including, an RNA dependent RNA polymerase
• produce -ve sense ssRNA template for genome replication

Question 13

Group V

Answer 13

• Rabies and Influenza
• enveloped
• ve sense ssRNA genome
• must carry their own RNA dependent RNA polymerase for mRNA production and genome replication
• produce +ve sense ssRNA template for genome replication

Question 14

Group VI

Answer 14

• HIV
• enveloped and diploid copes of +ve sense ssRNA genome
• replication occurs in the nucleus
• reverse transcriptase (RNA-dependent DNA polymerase )
• provirus

Question 15

Group VII

Answer 15

• hepatitis B virus
• contain a partially dsDNA genome and replicate in the nucleus
• Once inside the host cell the partial dsDNA is converted to complete dsDNA which is transcribed into mRNA and pre-genomic (+ve) sense, ssRNA
• The pre-genomic (+ve) sense, ssRNA intermediate is first encapsidated prior to reverse transcription by RNA-dependent DNA-polymerase (reverse transcriptase) to form new partial dsDNA genomes
• The HBV DNA may integrate into the host genome causing chronic infection leading to hepatocellular carcinoma (HCC)

Question 16

Hepatitis D Virus (HDV)

Answer 16

• HDV genome comprises of a (-ve) sense, ssRNA.
• HDV is a defective virus that replicates in the nucleus and requires HBV envelope proteins (HBsAg) during assembly and release

Question 17

Replication of HDV

Answer 17

Following infection, HDV genome is translocated to the nucleolus
• HDV genome is transcribed by cellular RNA polymerases and mRNA is translated in the cytoplasm
• Hepatitis D antigen is translocated to the nucleolus
• HDV nucleocapsid associates with HBsAg in the cytoplasm during assembly and release from infected cells

Question 18

What is recombination

Answer 18

Viruses can infect the same host and recombine with low frequency

Question 19

Complementation

Answer 19

-occurs when one or both viruses which are simultaneously infecting the host cell have defective function(s) but at different gene location.
-they fix each other though
E.g - relationship btw helper HBV and defective HDV

Question 20

Antigenic drift-

Answer 20

evolution due to small changes in the genome sequence within a define strain which usually occurs at a slower rate compared to antigenic shift e.g. influenza virus, rhinovirus

Question 21

Antigenic shift

Answer 21

usually occurs in segmented viruses, notably influenza virus, resulting in exchange (reassortment) of RNA segments between two different influenza viruses that subsequently gives rise to a highly pathogenic (reassorted) strain virus

Question 22

Phenotypic mixing or transcapsidation

Answer 22

non-genetic interaction in which virus particles released from a cell that is infected with two different viruses have components from both the infecting agents, but with a genome from one of them, e.g, poliovirus, myxovirus

Question 23

Pseudotypes

Answer 23

non-genetic interaction in which nucleocapsid of one virus acquires envelope from another type of virus.