viruses 2 - Flashcards
Parvovirus
requires cells underdoing DNA synthesis to replicate
Papovavirus
stimulates cell growth and DNA synthesis
Hepadnavirus
stimulates cell growth cell makes RNA intermediate ,encodes a reverse transcriptase
Adenovirus
stimulates cellular DNA synthesis and encodes its own polymerase
Herpesvirus
stimulates cell growth ,encodes its own polymerase and enzymes to provide deoxyribonucleotides for DNA synthesis ,establishes latent infection in host
Poxvirus
encodes its own polymerases and enzymes to provide deoxyribonucleotides for DNA synthesis replication replication machinery and transcription machinery in the cytoplasm
Group 1 -
- e.g herpesvirus
- non -enveloped or enveloped
- double stranded DNA genome
- replicate in the nucleus (*poxvirus)
Early proteins in group 1
Target genome replication : like viral DNA polymerase
Late proteins in group 1
- Parvovirus
- structural
- translocation back into the nucleus to form a capsid
Group II
- 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
Group III
- 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.
Group IV -Poliovirus
- 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
Group V
- 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
Group VI
- HIV
- enveloped and diploid copes of +ve sense ssRNA genome
- replication occurs in the nucleus
- reverse transcriptase (RNA-dependent DNA polymerase )
- provirus
Group VII
- 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)
Hepatitis D Virus (HDV)
- 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
Replication of HDV
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
What is recombination
Viruses can infect the same host and recombine with low frequency
Complementation
-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
Antigenic drift-
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
Antigenic shift
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
Phenotypic mixing or transcapsidation
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
Pseudotypes
non-genetic interaction in which nucleocapsid of one virus acquires envelope from another type of virus.
