Growing Viruses • Animal viruses may be grown in living animals or in embryonated eggs. Figure 13.7
Dec 31, 2015
Growing Viruses
• Animal viruses may be grown in living animals or in embryonated eggs.
Figure 13.7
Growing Viruses
• Animal and plants viruses may be grown in cell culture.– Continuous cell lines may be maintained indefinitely.
Figure 13.8
Virus Identification• Cytopathic effects
• Serological tests– Detect antibodies against viruses in a patient.– Use antibodies to identify viruses in
neutralization tests, viral hemagglutination, and Western blot.
• Nucleic acids– RFLPs– PCR
Virus Identification
Figure 13.9
Multiplication of Bacteriophages (Lytic Cycle)
• Attachment: Phage attaches by tail fibers to host cell.
• Penetration: Phage lysozyme opens cell wall, tail sheath contracts to force tail core and DNA into cell.
• Biosynthesis: Production of phage DNA and proteins.
• Maturation: Assembly of phage particles.• Release: Phage lysozyme breaks cell wall.
1
2
3
Figure 13.11, steps 1–3, 6–7
4
Figure 13.11, steps 4–5, 8
One-Step Growth Curve
Figure 13.10
• Lytic cycle: Phage causes lysis and death of host cell.
• Lysogenic cycle: Prophage DNA incorporated in host DNA.
The Lysogenic Cycle
Figure 13.12
2
3
4
5
6
Specialized Transduction
Figure 13.13
Multiplication of Animal viruses• Attachment: Viruses attach to cell membrane.• Penetration by endocytosis or fusion.• Uncoating by viral or host enzymes.• Biosynthesis: Production of nucleic acid and proteins.• Maturation: Nucleic acid and capsid proteins assemble.• Release by budding (enveloped viruses) or rupture.
Attachment, Penetration, and Uncoating
• Pinocytosis
Figure 13.14a
Attachment, Penetration, and Uncoating
• Fusion
Figure 13.14b
Release of an Enveloped Virus by Budding
Figure 13.20
Multiplication of DNA Virus
Figure 13.15
+ Sense Strand (+ Strand) RNA Virus
Figure 13.17a
Maturationand release
Entryand uncoating
Translation and synthesisof viral proteins
RNA replication by viral RNA-dependent RNA polymerase
Uncoating releasesviral RNA and proteins.
Nucleus
Attachment
Viralprotein
Capsidprotein
Cytoplasm
Host cell
– strand is transcribedfrom + viral genome.
+ strand
mRNA is transcribedfrom the – strand.
Capsid
RNA
Viralgenome(RNA)
ssRNA; +or sense strand;Picornaviridae
(a)
— Antisense Strand (— Strand) RNA Virus
Figure 13.17b
Maturationand release
Entryand uncoating
Translation and synthesisof viral proteins
RNA replication by viral RNA-dependent RNA polymerase
Uncoating releasesviral RNA and proteins.
Nucleus
Attachment
Viralprotein
Capsidprotein
Cytoplasm
Host cell
– strands areincorporatedinto capsid
The + strand (mRNA) must firstbe transcribed from the – viralgenome before proteins canbe synthesized.
Additional – strands aretranscribed from mRNA.
Capsid
RNA
Viralgenome(RNA)
ssRNA; – orantisense strand;Rhabdoviridae
(b)
Double-Stranded RNA Virus
Figure 13.17c
Maturationand release
Entryand uncoating
Translation and synthesisof viral proteins
RNA replication by viral RNA-dependent RNA polymerase
Uncoating releasesviral RNA and proteins.
Nucleus
Attachment
Viralprotein
RNA polymerase initiates production of– strands. The mRNA and – strands form thedsRNA that is incorporated as new viral genome.
Cytoplasm
Host cell
mRNA is produced inside thecapsid and released into thecytoplasm of the host.
Capsid
RNA
Viralgenome(RNA)
dsRNA; + or sensestrand with – or antisense strand; Reoviridae
Capsid proteins and RNA-dependent RNA polymerase
(c)
Pathways of Multiplication for RNA-Containing Viruses
Figure 13.17
Multiplication of a Retrovirus
Figure 13.19
DNA and RNA Viruses Compared
• DNA: Cellular enzyme transcribes viral DNA in nucleus.
• DNA, reverse transcriptase: Cellular enzyme transcribes viral DNA in nucleus; reverse transcriptase copies mRNA to make viral DNA.
• RNA, + strand: Viral RNA is a template for synthesis of RNA polymerase.
DNA and RNA Viruses Compared
• RNA – strand: Viral enzyme copies viral RNA to make
mRNA in cytoplasm.
• RNA, double-stranded: Viral enzyme copies – strand
RNA to make mRNA in cytoplasm.
• RNA, reverse transcriptase: Viral enzyme copes viral
RNA to make DNA in cytoplasm.
Cancer
• Activated oncogenes transform normal cells into cancerous cells.
• Transformed cells have increased growth, loss of contact inhibition, tumor specific transplant and T antigens.
• The genetic material of oncogenic viruses becomes integrated into the host cell's DNA.
Oncogenic Viruses• Oncogenic DNA
viruses– Adenoviridae– Heresviridae– Poxviridae– Papovaviridae– Hepadnaviridae
• Oncogenic RNA viruses
• Retroviridae• Viral RNA is
transcribed to DNA which can integrate into host DNA
• HTLV 1• HTLV 2
• Latent viral infections– Virus remains in asymptomatic
host cell for long periods.• Cold sores, shingles
• Presistent viral infections– Disease processes occurs over a
long period; generally is fatal.• Subacute sclerosing panencephalitis
(measles virus)
Figure 13.21