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What is a Virus? • Virus: A biological particle composed of nucleic acid and protein • Intracellular Parasites: organism that must “live” inside a host • Not made of cells • Can’t reproduce on own • Don’t metabolize energy • Don’t perform cellular processes • Reproduce with help of host • Contain nucleic acid • Adapt to surroundings • 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 Virus Video • 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 cellcell is destroyed and new viruses escape 1st Step: Attachment – Virus lands on cell membrane – Virus attaches to a cell receptor – Virus acts as key; receptor acts as lock 2nd Step: Entry – Virus enzyme weakens cell membrane – DNA/RNA enters the host cell Another way viruses may enter a cell… through phagocytosis 3rd 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 4th Step: Assembly – Virus proteins are assembled into new viruses 5th 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 1st step: Attachment Same 2nd Step: Entry Same 3rd 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 Provirus Procell virus DNA Provirus 4th Step: Assembly: new viruses are assembled in many cells 5th 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 How is HIV contracted? High Risk Activities Low Risk Activities • High risk activities: • Low risk activities: – 1) Sex (oral, vaginal, anal) – 2) Sharing needles (tattoos, piercings, drugs) – 3) Mother to child in womb – 4) Breast milk – 5) Blood transfusions HIV Prevention • 100% Effective: Abstinence (not participating in sexual acts) • If sexually active: Latex condoms are the only forms of birth control that prevent STDs and pregnancy • If drug user: Change needles 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 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 Female Transmission of HIV (2006) Male Transmission of HIV (2006) Want more stats? Go to the Centers for Disease Control’s Website http://www.cdc.gov/hiv/topics/surveillance/united_states.htm 1. 2. 3. 4. 5. 6. 7. 8. True or False: All viruses have a capsid, nucleic acid, and tail fibers. List 3 reasons why viruses may be living? Nonliving? What is the virus capsid made from? What type of organism do phages infect? In order list the stages of the lytic/lysogenic cycles. In which stage… • does the host cell explode? • are virus proteins built to make new viruses? • is a provirus created? • does a virus connect with the host cell’s receptors? Name the enzyme found within retroviruses. The picture shows the normal stages of protein synthesis. Fill in the question marks with the words: Translation, Protein, Transcription, DNA