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Virus: A biological particle composed of nucleic acid and protein Intracellular Parasites: organism that must “live” inside a host 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 Reproduce They have DNA or RNA They can adapt to surroundings The have organization 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 Cannot reproduce w/o a host cell • Virulent: cause disease Bacteriophages (infect bacteria) are often studied • Replication is similar with many animal viruses 1st 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 endocytosis 2nd Step: Entry • Virus enzyme weakens cell membrane • Genetic material (DNA or RNA) enters host cell 3rd Step: Replication • Virus DNA/RNA uses ribosomes to make virus proteins • Proteins created by transcription/translat ion • Virus proteins make new virus parts 4th Step: Assembly (formation) • New virus parts are assembled in the cytoplasm 5th Step: Lysis & Release • Virus enzyme causes cell membrane to “lyse” • New viruses are released to find new host • Cycle repeats 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 1st step: Attachment = Same • 2nd Step: Entry = Same 3rd step: Replication • Virus DNA combines with cell DNA, and waits… • Cell divides as usual • Each new cell will have virus DNA inside 4th Step: Assembly Same, except many new viruses are being assembled in many cells • 5th Step: Release Same, except many cells “lyse” releasing many more viruses 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