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