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

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

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 to lyse (burst) Viruses are released to find new host Cycle repeats

All stages on one slide Attachment Entry Replication & Assembly Release

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 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: After long period of dormancy, viral DNA is triggered and 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

The Lysogenic Cycle The Lytic Cycle This happens VERY QUICKLY Examples Virus attaches to host cell Host cell assembles virus Virus is released to infect other cells This happens VERY QUICKLY Usually makes person sick within 24-72 hours Examples Flu/common cold Chicken pox HIV Virus attaches to host cell Viral DNA is dormant (hidden) inside host cell DNA Host cell replicates with viral DNA inside Viral DNA is then triggered by environmental factors and begins assembly and release This takes a LONG PERIOD OF TIME May take years before person gets sick from this virus Examples Shingles (dormant when a person gets the chicken pox) AIDS (dormant when a person gets HIV)

HIV/AIDS

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?