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RNA

Capsomere of capsid

Capsomere RNA Membranous envelope Capsid

Head DNA

Tail sheath

Tail fiber

80 ! 225 nm

Glycoproteins

80–200 nm (diameter)

Glycoprotein

70–90 nm (diameter) 18 ! 250 nm

20 nm Tobacco mosaic virus

(a) (b) Adenoviruses (c) Influenza viruses (d) Bacteriophage T4 50 nm 50 nm 50 nm

1 Entry and uncoating

Transcription and manufacture of capsid proteins

Self-assembly of new virus particles and their exit from the cell

Capsid proteins

Viral DNA

mRNA

Viral DNA

HOST CELL Replication

Capsid DNA

VIRUS

2

3

4

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Phage DNA The phage injects its DNA.

Bacterial chromosome

Phage Tail fiber

Lytic cycle

The cell lyses, releasing phages.

Phage DNA circularizes.

Phage DNA and proteins are synthesized and assembled.

Daughter cell with prophage

Prophage exits chromosome.

Lysogenic cycle

Many cell divisions create many infected bacteria.

Prophage

Prophage is copied with bacterial chromosome.

Phage DNA integrates into bacterial chromosome.

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2"3$#&'/014'Capsid

RNA

Envelope (with glycoproteins)

mRNA

Template

ER

Capsid proteins

Viral genome (RNA)

Copy of genome (RNA)

New virus

HOST CELL

Glyco- proteins

Glycoprotein

Reverse transcriptase

HIV

RNA (two identical strands)

Viral envelope

Capsid

Viral RNA RNA-DNA hybrid

DNA

HOST CELL

Reverse transcriptase

NUCLEUS Provirus

Chromosomal DNA

RNA genome for the progeny viruses mRNA

New virus

1 !m

2009 pandemic H1N1 influenza A virus

2009 pandemic screening (b) (a)

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Prion

Normal protein

New prion

Original prion

Aggregates of prions

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