Ch 12: Viruses (Baltimore Classification)

group i

double stranded DNA virus

replicates within the host cell nucleus

herpesvirus

what is an example of group i?

group ii

starts with single stranded DNA but uses host cell’s DNA polymerase to generate complementary strand to make double strand

parvovirus

what is an example of group ii?

group iii

double stranded rna virus

replicates within host cell cytoplasm

RNA dependent polymerase

rna dependent rna polymerase

RdRp

(+) SS rna serves as template for new dsRNA

genome replication process for group iii

group iv

(+) SS RNA

positive sense single stranded RNA

coronavirus

example of group iv?

RdRp uses (+) SS RNA as template to synthesize complementary (-) RNA strand

(-) RNA strand serves as template for synthesis of new (+) single strand RNA

genome replication process for group iv

group v

negative sense single stranded RNA

genome replication process for group v

(+) SS RNA is used as a template to synthesize new complementary (-) RNA strand

group vi

single stranded RNA with a DNA intermediate

once viral RNA is inside host cell, it is reverse transcribed into complementary DNA (cDNA) by reverse transcriptase

influenza

example of group v virus

integrated viral DNA is transcribed by host RNA polymerase

genome replication for group vi

retrovirus

example of group vi

group vii

double stranded DNA with RNA intermediate

partially double stranded DNA is released in host nucleus and converted into DS closed circular DNA by host cell enzyme

hepadnavirus

example of group vii

cccDNA is transcribed as SS (+) strand

reverse transcriptase converts pre genomic RNA into partially double stranded RNA

genome replication process of group vii

hepadnavirus and retrovirus

viruses that carry reverse transcriptase

antigenic drift

more minor and rapid mutation

lead to minor changes in virus’ surface proteins

antigenic shift

major change and larger mutations

results in chimeric virus

reassortment of genome segments

leads to highly virulent strains of a virus

segmented genome

genome with individual genetic material “parts” that can be reordered to impact the generation of new strains

increases antibiotic resistance

virion binds to surface receptors (virus has no envelope)

endocytosis occurs

enters cytoplasm, transcription and translation occurs

exits by rupturing cell bc it’s non enveloped

steps of replication for papillomaviruses

basal cells group i

where does HPV end up integrating its DNA and what group is it?

E6 and E7

what oncogenes are increasingly expressed as a result of HPV?

HPV infection steps

HPV infects basal cells where it remains dormant

keratinocytes differentiate; virus replication is activated

shedding cells release HPV virions into environment (new variants are released and can spread to others)

hpv

small icosahedral

circular double stranded DNA

no envelope

encodes 8 genes

influenza

no fixed capsid

(-) SSrNA

8 chromosome segments

enveloped

uses RNA dependent RNA polymerase

group v

hemagglutinin

beginning attachment for influenza

neuraminidase

key player when releasing new variants

influenza infection steps

uses hemagglutinin to stick to host cell

cell uptakes virion

(-) RNA and RdRp are released and enter nucleus

transcription and translation of (+) occurs

virus pushes out from cell wall; neuraminidase helps viruses chop themselves free from cell so they can travel to infect other cells

broader explanation of influenza infection

attachment via HA spikes

entry thru endocytosis

replication via RdRp

assembly

budding with help of neuraminidase

hiv

retrovirus (group vi)

has (+) ssRNA, uses reverse transcriptase, has integrase and protease

hiv infection steps

HIV virion attaches, fuses to membrane and releases core into cytoplasm

core dissolves, RNA chromosomes are copied to make double stranded DNA

integrates into host chromosome, RNA transcripts are made

transcripts express capsid and reverse transcriptase proteins

RNA transcripts exit nucleus to form RNA dimers for progeny virions

env proteins are made, exported to cell membrane, assist packaging of RNA dimers, which are then released from cell

latent viral infection

viruses that remain in the body even after the main infection is over

ex) HIV (under certain conditions it can become active and cause infection again)