Virus Replication

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3 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

4 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) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

5 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

6 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

7 Bacteriophages: The Lytic Cycle Lytic cycle may be divided into five stages: – Attachment – Penetration – Biosynthesis – Maturation – Release

8 The Bacteriophages: The Lysogenic Cycle Phage becomes a prophage – Becomes integrated into the host genome – Becomes latent – May later reenter the lytic cycle

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