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Bacteria and Viruses AP Biology Bacteria • • • • • • • Very diverse Most abundant Prokaryotic Single chromosome; some have a plasmid Usually a cell wall Prokaryotic fission Great diversity in metabolism Three Shapes • Coccus—pl. cocci • Bacillus—pl. bacilli • Spirillum—pl. spirilla spherical rod spiral Three Shapes Three Shapes Three Shapes Three Shapes bacillus coccus Three Shapes • Diplococcus: chain of two • Streptococcus: chain of many • Tetrad: ball of four • Sarcinae: larger ball • Staphylococci: bunch of grapes Three Shapes Three Shapes Three Shapes Three Shapes Typical Cell Typical Cell Gram Stain • Bacteria are often identified as gram positive or gram negative • This refers to their reaction to a staining method developed by Hans Christian Gram • The structure of the cell wall determines the response + - Gram Stain • Gram positive appears purple or blue because the cell wall contains more peptidoglycan, which holds the violet stain. • Gram negative appears pink or red. These have less peptidoglycan, which does not hold the violet dye. • After the violet stain, they are rinsed in a red dye. The gram negative pick up only the second color. Gram Stain Gram Stain Prokaryotic Fission • DNA is copied • New cell membrane and new cell wall sections are made • Cells separate Prokaryotic Fission Conjugation • A tube connects the two bacteria • The plasmid is replicated and transferred to the recipient cell Classification • Eubacteria: most abundant; now includes the bluegreen algae and other monerans • Archaebacteria: three groups based on metabolism Viruses • Are they alive? • Do they exhibit the characteristics of life? • What diseases do they cause? Viruses • Non-cellular • Infectious agent • Consist only of protein coat surrounding genetic material; coat contains proteins that bind with a receptor protein • Genetic material can be DNA or RNA • Range from 4 genes to several hundred genes Viruses • 4 typical body plans • Helical • Polyhedral-many sided coat • T-even • Enveloped • Page 356 Viruses • Cannot reproduce itself • Must have a host cell • Mutates frequently, outer protein coat changes • That’s why we can’t make some vaccines and why we get some illnesses over and over again RNA viruses are called retroviruses; They must make cDNA from RNA and then proceed with replication Viruses • Viruses can attack animal cells, plant cells, and bacterial cells • Viruses which attack bacteria are called bacteriophages, or phages • Notice different types by shape Viral reproduction in host cells • Virus matches a receptor on host cell membrane • Enters by endocytosis • Directs replication of viral DNA and the manufacture of new viruses • Damages or destroys the cell, resulting in symptoms Viruses • Replication in phages takes one of two pathways: lytic or lysogenic • Lytic progresses right away • Lysogenic may be latent and reactivated later Viruses • Lytic cycle in a human cell Viruses • Lyse means “to burst” • The lytic cycle always results in the death of the host cell • Page 358 in text Computer generated picture of the polio virus Smaller than Viruses • Prions are small proteins that cause diseases of the nervous system—Mad Cow Disease • Viroids are tightly folded strands or circles of RNA that resemble introns— mostly plant diseases Prions Viroid plant infections Influenza virus