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Viruses

Viruses. What is a Virus?. Virus : A biological particle composed of nucleic acid and protein Intracellular Parasites : organism that must “ live ” inside a host. Reproduce with help of host Contain nucleic acid Adapt to surroundings Have organization. Not made of cells

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Viruses

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  1. Viruses

  2. What is a Virus? • Virus: A biological particle composed of nucleic acid and protein • Intracellular Parasites: organism that must “live” inside a host

  3. Reproduce with help of host Contain nucleic acid Adapt to surroundings Have organization Not made of cells Can’t reproduce on own Don’t metabolize energy Don’t perform cellular processes Are viruses alive? No Yes

  4. Virus Parts • All Have: 1) Capsid: coat of protein that surrounds nucleic acid 2) Nucleic Acid: RNA or DNA • Some Have: • Tail Fibers: Used for attachment (not legs) • Shapes vary

  5. Viral Replication • Bacteriophages (viruses that attack bacteria) are often studied • Replication is similar with many animal viruses • Two “life” cycles: Lytic & Lysogenic Dozens of phage viruses attacking an E. coli bacteria cell The bacteria cell is destroyed and new viruses escape

  6. The Lytic Cycle 1st Step: Attachment • Virus lands on cell membrane • Virus attaches to a cell receptor • Virus acts as key; receptor acts as lock

  7. The Lytic Cycle 2nd Step: Entry • Virus enzyme weakens cell membrane • DNA/RNA enters the host cell Another way viruses may enter a cell… through phagocytosis

  8. The Lytic Cycle 3rd Step: Replication • Virus DNA/RNA uses ribosomes to make virus proteins • Virus proteins created by transcription/ translation transcription translation Viral DNA Viral RNA Viral Proteins

  9. The Lytic Cycle 4th Step: Assembly • Virus proteins are assembled into new viruses

  10. The Lytic Cycle 5th Step: Release • Virus enzyme causes cell membrane to lyse (burst) • Viruses are released • Cycle repeats

  11. All stages on one slide Attachment Entry Replication & Assembly Release

  12. The Lysogenic Cycle 1st step: Attachment Same 2nd Step: Entry Same

  13. The Lysogenic Cycle • 3rd step: Replication • Provirus Created • Virus DNA combines with cell DNA • Infected cell divides by mitosis and copies the provirus • Each new cell will contain the provirus Virus DNA Pro-virus cell DNA Pro-virus Pro-virus

  14. The Lysogenic Cycle 4th Step: Assembly: new viruses are assembled in many cells 5th Step: Release many cells burst releasing many more viruses

  15. The viral DNA become active and starts making new viral proteins The infected cells burst…releasing the new viruses

  16. The Retrovirus

  17. Type of RNA virus Contain enzyme called “reverse transcriptase” Steps 1) Virus RNA enters host cell 2) Reverse transcription changes the virus RNA into DNA 3) Virus DNA combines with cell DNA (provirus created) 4) Cell divides and copies the virus 5) Eventually, the viral DNA becomes active Retroviruses

  18. What is AIDS? New Exposures to HIV (2006) • Acquired Immunodeficiency Syndrome • AIDS results when: • 1) Amount of T-cells drop (200 T-cells per 1mm³ blood) • 2) Multiple symptoms/infections appear • Rash, fever, headache, sore throat, swollen lymph nodes • Therefore, the HIV virus causes the disease AIDS by killing your T-cells Gender of those living with HIV (2003)

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