What is a Virus Virus A biological particle

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

Are viruses alive? • Not made of cells • Reproduce with • Can’t reproduce on own help of host • Contain nucleic • Don’t metabolize acid energy • Adapt to • Don’t perform cellular surroundings processes • Have organization

• 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

• 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 The bacteria cell is destroyed and new viruses escape

1 st Step: Attachment – Virus lands on cell membrane – Virus attaches to a cell receptor – Virus acts as key; receptor acts as lock

2 nd Step: Entry – Virus enzyme weakens cell membrane – DNA/RNA enters the host cell Another way viruses may enter a cell… through phagocytosis

3 rd Step: Replication – Virus DNA/RNA uses ribosomes to make virus proteins – Virus proteins created by transcription/ translation Viral DNA transcription Viral RNA translation Viral Proteins

4 th Step: Assembly – Virus proteins are assembled into new viruses

5 th Step: Release – Virus enzyme causes cell membrane to lyse (burst) – Viruses are released – Cycle repeats

Attachment All stages on one slide Entry Replication & Assembly Release

1 st step: Attachment Same 2 nd Step: Entry Same

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

4 th Step: Assembly: new viruses are assembled in many cells 5 th Step: Release many cells burst releasing many more viruses

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

Retroviruses • 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

What is AIDS? New Exposures to HIV (2006) Gender of those living with HIV (2003) • Acquired Immunodeficiency Syndrome • AIDS results when: – 1) Amount of T-cells drop (200 T-cells per 1 mm³ 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