1 / 15

Viruses

Viruses. Chapter 19. Viral Structure. Very small (smaller than ribosomes !) Genetic material is double or single-stranded DNA or double or single-stranded RNA All have a capsid – protein shell that surrounds the DNA or RNA

lanza
Télécharger la présentation

Viruses

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Viruses Chapter 19

  2. Viral Structure • Very small (smaller than ribosomes!) • Genetic material is double or single-stranded DNA or double or single-stranded RNA • All have a capsid – protein shell that surrounds the DNA or RNA • Some viruses also have viral envelopes which surround the capsid and aid in viral infection of host cells

  3. Viral Structure

  4. Viruses are Host Specific • Viruses can only infect a limited variety of hosts (certain organisms and particular cells)

  5. Viral Infection Cycles • Viruses inject DNA into host cell, then either the lytic or lysogenic cycle begins, depending on certain conditions in the host cell

  6. Lytic Cycle • Virus takes over the cell organelles to make new copies of viral DNA and protein coats (capsids). Viral parts self-assemble, cell lyses, and viruses are released to infect other cells • Shorter cycle

  7. Lysogenic Cycle • Viral DNA becomes incorporated into the host cell’s DNA • viral DNA is called a Prophage • The prophage is replicated with the host cell’s DNA • The cell can enter the lytic cycle at any time (HIV can hide out in the lysogenic cycle for years which is why we don’t see the effects for 5-10 years)

  8. Lytic & Lysogenic Cycles

  9. Classes of Animal Viruses • Classified by genome type: • dsDNA, ssDNA, dsRNA, ssRNA • These can be a template for mRNA or DNA synthesis

  10. ssRNA is template for mRNA • Influenza, ebola, measles, mumps, rabies • Use RNA to make mRNA, then makes capsid and envelope proteins, assembles new viruses with copies of RNA genome

  11. ssRNA is template for DNA • These are called retroviruses because they use reverse transcriptase to transcribe DNA from viral RNA • Viral DNA called a provirus is then incorporated into host chromosomal DNA in the nucleus and stays in the host genome • Host transcribes viral DNA into mRNA, makes viral proteins which are assembled into new viruses • Ex: HIV, RNA tumor viruses like leukemia

  12. HIV Reproductive Cycle

  13. Viroids • Extremely small RNA molecules that infect plants, causing errors in regulatory systems that control growth

  14. Prions • Misfolded, infectious proteins that cause misfolding in normal proteins in animals • Destroy brain cells, causing brain degeneration • No cure for prion diseases – the process by which they cause infection is not understood • Mad Cow Disease (in cows) and CreutzfeldtJakob Disease (in humans)

  15. Vaccines • Harmless variants of pathogens (like viruses) that can stimulate the immune system to produce memory cells for the pathogen (in case of actual pathogen exposure at a later time) • Vaccines are generally very effective, but they are usually only preventative (HPV) • Viral infections cannot usually be cured by medicine • Antibiotics do NOT help because viruses are NOT living cells • Some anti-viral drugs interfere with nucleic acid synthesis and enzymes used for viral assembly – interferons like Tamiflu

More Related