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VIRUSES.

VIRUSES. Viral replication  genetic variation Viral Infection  can introduce genetic variation in hosts. Structure. Composition: n ucleic a cid (viral DNA = prophage ) surrounded by a p rotein coat Very small! (~ 20nm ) Capsid – Protein shell that surrounds genetic material

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VIRUSES.

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  1. VIRUSES. Viral replication genetic variation Viral Infection can introduce genetic variation in hosts

  2. Structure • Composition: nucleic acid (viral DNA = prophage) surrounded by a protein coat • Very small! (~20nm) • Capsid – Protein shell that surrounds genetic material • Viral Envelope – surrounds the capsid of some viruses, helping to infect hosts

  3. Bacteriophage • Viruses that infect bacteria cells • Aka: Phages

  4. Replication • Host Range – Range of hosts a virus can infect  can only infect a limited variety of hosts (ex. Human cold virus can only infect upper respiratory tract)

  5. a. Lytic Cycle • Bacteriophage injects its DNA into host cell and takes over the cell’s machinery to make new copies of the viral DNA and protein coats • These self assemble (component assembly model) and host bursts open (lysis), releasing new viruses

  6. b. Lysogenic Cycle • Bacteriophage DNA is incorporated into hosts DNA, replicated by host along with its own genome, can enter lytic cycle (but not always) • Host is not killed • Can sometimes result in new properties for the host

  7. Transduction (in Bacteria) • Bacterial DNA is ‘accidentally’ picked up into phages’ (viruses) DNA during lytic cycle and integrated into a new bacteria (host) cells DNA

  8. Replication • Highly effective replicative capabilities - allows for rapid evolution and acquisition of new phenotypes • Allows for mutations • Lack error-checking mechanisms (higher rates of mutations) • Related viruses can combine/recombine info if same host is infected

  9. Retroviruses • RNA viruses – use the enzyme reverse transcriptase to transcribe DNA from RNA template • New DNA permanently integrates into DNA of animal cell • Host (animal) transcribes viral DNA into RNA used to make viral proteins

  10. HIV • Human Immunodeficiency Virus  causes Acquired Immunodeficiency Syndrome (AIDS) • Retrovirus • HIV infects cells in the human immune system (white blood cells) • Rapid evolution of a virus within host contributes to pathogenicity (deadliness) of viral infection

  11. Similar pathogens in plants and animals: • Viroid – Circular RNA molecules that infect plants causing errors in regulatory systems that control plant growth • Prions – misfolded, infectious proteins that cause misfolding in normal proteins they come in contact with in various animal species (ex: Mad Cow Disease)

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