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Published byJuniper Stokes Modified over 9 years ago
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Virus: A biological particle composed of nucleic acid and protein Intracellular Parasites: organism that must “live” inside a host What is a Virus? viruses 50-200 nm prokaryotics cells 200-10,000 nm prion 2-10 nm viroids 5-150 nm eukaryotics cells 10,000-100,000 nm 100 nm 1 nanometer (nm) = one billionth of a meter
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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
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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
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Virus Video
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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
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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
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2 nd Step: Entry –Virus enzyme weakens cell membrane –Genetic material (DNA or RNA) enters host cell endocytosis
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3 rd Step: Replication –Virus DNA/RNA uses ribosomes to make virus proteins –Virus proteins created by transcription/ translation transcriptiontranslation Viral DNAViral RNAViral Proteins
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4 th Step: Assembly –New virus proteins are assembled in the cytoplasm
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5 th Step: Release –Virus enzyme causes cell membrane lyse (burst) –Viruses are released to find new host –Cycle repeats
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Attachment Entry Replication & Assembly Release All stages on one slide
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1 st step: Attachment = Same as lytic cycle 2 nd Step: Entry = Same as lytic cycle
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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
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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
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The viral DNA become active and starts making new viral proteins The infected cells burst…releasing the new viruses
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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?
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