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

Reproduce Have nucleic acid Adapt to surroundings Have organization Not made of cells or organelles Can’t reproduce on own Don’t metabolize energy Don’t perform cellular processes

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 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 cell 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 No attachment = No infection

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

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

4 th Step: Assembly –New virus proteins are assembled in the cytoplasm

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

Attachment Entry Replication & Assembly Release All stages on one slide

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

cell DNA Pro- virus 3 rd 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

4 th Step: Assembly: Same, except many new viruses are assembled in many cells 5 th Step: Release Same, except 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

1.True or False: All viruses have a capsid, nucleic acid, and tail fibers. 2.List 3 reasons why viruses may be living? Nonliving? 3.What is the virus capsid made from? 4.What type of organism do phages infect? 5.In order list the stages of the lytic/lysogenic cycles. 6.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? 7.Which two objects make up a provirus? 8.Which virus “life” cycle is considered the most harmful? Why?