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 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: 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
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?