Viruses

1 nanometer (nm) = one billionth of a meter What is a Virus? 1 nanometer (nm) = one billionth of a meter 100 nm eukaryotics cells 10,000-100,000 nm viroids 5-150 nm viruses 50-200 nm prokaryotics cells 200-10,000 nm prion 2-10 nm Virus: A biological particle composed of nucleic acid and protein Intracellular Parasites: organism that must “live” inside a host

Are viruses alive? No Yes Not made of cells or organelles Can’t reproduce on own Don’t metabolize energy Don’t perform cellular processes Reproduce Have 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) Shape & size varies Virus Parts

Virus Video

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

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 No attachment = No infection

The Lytic Cycle 2nd Step: Entry Virus enzyme weakens cell membrane endocytosis 2nd Step: Entry Virus enzyme weakens cell membrane Genetic material (DNA or RNA) enters host cell

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

The Lytic Cycle 4th Step: Assembly New virus proteins are assembled in the cytoplasm

The Lytic Cycle 5th Step: Release Virus enzyme causes cell membrane lyse (burst) Viruses are released to find new host Cycle repeats

All stages on one slide Attachment Entry Replication & Assembly Release

Review 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? Which two objects make up a provirus? Which virus “life” cycle is considered the most harmful? Why?

The Lysogenic Cycle

The Lysogenic Cycle 1st step: Attachment = Same as lytic cycle 2nd Step: Entry = Same as lytic cycle

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 Provirus can remain dormant Virus DNA Pro-virus cell DNA Pro-virus Pro-virus

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

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

Reverse Transcription 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 fuses with cell DNA (provirus created) Viral DNA lays dormant 4) Infected cell divides and spreads the virus 5) Eventually, the viral DNA becomes active in many cells Viral DNA  Viral RNA  Viral proteins Normal Transcription DNA  RNA Reverse Transcription RNA  DNA

How is HIV contracted? High risk activities: Low risk activities: 1) Sex (oral, vaginal, anal) 2) Sharing needles (tattoos, piercings, drugs) Low risk activities: 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? 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

What is AIDS? 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)

What is AIDS? 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 2009: New Infections MSM: Men having sex with men IDU: Intravenous drug users (share needles) MSM/IDU: Men who share needles and have sex with men

Female Transmission of HIV What is AIDS? 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)

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Review Name the enzyme found within retroviruses. The picture shows the normal steps of protein synthesis. Fill in the question marks with the words: Translation, Protein, Transcription, DNA The picture below shows the steps of a retrovirus. Fill in the question marks with the words: viral RNA, transcription, translation, reverse transcription, viral DNA