Virus Replication

Animation

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The Viruses: Structure

• Generally smaller than 200 nm in diameter• Each type has at least two parts

– Capsid: Outer layer composed of protein subunits• Some enveloped by membrane• Others “naked”

– Nucleic acid core: DNA or RNA

• Vary in shape from thread-like to polyhedral

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The Viruses: Structure

Covering

Inner core

Capsid (protein)

Envelope (not found in all viruses)

Virus particle

Nucleic acid molecule (DNA or RNA)

Various proteins (enzymes)

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Viral Reproduction

• Gain entry into specific host cell – Capsid (or spikes of the envelope) adhere to specific

receptor sites on the host cell surface.

• Viral nucleic acid then enters a cell– Viral genome codes for production of protein units in the

capsid.

• Relies on host cell enzymes, ribosomes, transfer RNA (tRNA), and ATP for its own replication

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The Bacteriophages: Reproduction

• Bacteriophages – Viruses that infect bacterial cells

• Portions of capsid adhere to specific receptor on the host cell

• Viral nucleic acid enters the cell• Once inside, the virus takes over metabolic

machinery of the host cell

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Bacteriophages: The Lytic Cycle

• Lytic cycle may be divided into five stages:– Attachment– Penetration– Biosynthesis– Maturation– Release

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The Bacteriophages: The Lysogenic Cycle

• Phage becomes a prophage– Becomes integrated into the host genome– Becomes latent– May later reenter the lytic cycle

Animation

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