3.  Virus: A biological particle composed of nucleic acid and protein  Intracellular Parasites: organism that must “live” inside a host

4.  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 don’t have both DNA and RNA  They do not metabolize energy

5.  All Have: 1) Capsid: coat of protein that surrounds DNA or RNA 2) Nucleic Acid: RNA or DNA  Some Have: Tail Fibers: Used for attachment (not legs)  Shapes vary

6.  Cannot reproduce w/o a host cell Virulent: cause disease  Bacteriophages (infect bacteria) are often studied Replication is similar with many animal viruses

7.  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

8.  2 nd Step: Entry Virus enzyme weakens cell membrane Genetic material (DNA or RNA) enters host cell endocytosis

9.  3 rd Step: Replication Virus DNA/RNA uses ribosomes to make virus proteins Proteins created by transcription/translat ion Virus proteins make new virus parts

10.  4 th Step: Assembly (formation) New virus parts are assembled in the cytoplasm

11.  5 th Step: Lysis & Release Virus enzyme causes cell membrane to “lyse” New viruses are released to find new host Cycle repeats

12.  If DNA Virus: 1) Viral DNA injected 2) Viral DNA transcribed into viral mRNA 3) Viral mRNA translated into viral proteins  If RNA Virus: 1) Viral RNA injected 2) Viral mRNA translated into viral proteins

13.  1 st step: Attachment = Same 2 nd Step: Entry = Same

14.  3 rd step: Replication Virus DNA combines with cell DNA, and waits… Cell divides as usual Each new cell will have virus DNA inside

15.  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

16.  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