Reproduce They have DNA or RNA They can adapt to surroundings The have organization They are not made of cells or organelles They cannot reproduce without a host They do not metabolize energy They do not perform cellular processes

Composed of protein coat & nucleic acid Bacteriophages (infect bacteria) are often studied –Replication is similar with many animal viruses

1 st Step: Attachment –Virus lands on cell membrane –Virus attaches to a cell receptor –No attachment = No infection –Virus acts as a “key” to the receptor

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

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

5 th Step: Lyse & Release –Virus enzyme causes cell membrane to “lyse” –Viruses are released to find new host –Cycle repeats

1 st step: Attachment = Same 2 nd Step: Entry = Same

3 rd step: Replication –Virus DNA combines with cell DNA, and waits Provirus = cell DNA + viral DNA –Cell divides by mitosis –Each new cell will contain the provirus

4 th Step: Assembly Same, except many new viruses are being assembled in many cells 5 th Step: Release Same, except many cells “lyse” releasing many more viruses

Retroviruses Type of RNA virus that contains the enzyme Reverse Transcriptase 1) Virus RNA is injected into cell 2) Ribosome uses virus RNA to create virus DNA 3) Virus DNA combines with cell DNA (becomes latent) 4) Once active, normal steps of transcription/translation followed

How is HIV contracted? High 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

MSM = men having sex with men IDU = intravenous drug users