Bacteria and Viruses

1
Bacteria and Viruses

• Starr/Taggarts
• Biology
• The Unity and Diversity of Life, 9e
• Chapter 22

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Key Concepts

• The simplest forms of life are bacteria
• Bacteria are the only prokaryotes
• Bacteria reproduce by binary fission
• The first living organisms on earth were bacteria
• Different lineages of organisms arose from
  bacteria

3
Key Concepts

• A virus is an infectious particle
• Viruses are non-cellular
• Almost all viral multiplication cycles proceed
  through the same 5 steps
• Microorganisms have been adapting, are diverse,
  and are surviving and replicating like us

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Characteristics of Bacteria

• Metabolic Diversity
• Photoautotrophic
• Chemoautotrophic
• Heterotrophs
• Sizes and Shapes
• 1 - 10 micrometers
• Coccus
• Bacillus
• Spirillum

• Structures
• Cell walls
• Peptidoglycan
• Membrane
• Glycocalyx
• DNA in cytoplasm
• Flagella
• Gram strain

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Bacterial Structure
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Prokaryotic Fission
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Prokaryotic Fission
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Prokaryotic Fission
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Bacterial Classification

• Numerical taxonomy
• Gene sequencing and comparative biochemistry

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Archaebacteria

• Methanogens
• Swamps, sewage
• Halophiles
• Brackish ponds, salt lakes, hydrothermal seafloor
  vents
• Extreme Thermophiles
• Acidic soils, hot springs, coal mines,
  hydrothermal vents

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Eubacteria

• Photoautotrophic
• Cyanobacteria
• Ponds and freshwater
• Chemoautotrophic
• Environment
• Cycling of N2 , S2

• Chemoheterotrophic
• Most bacteria
• Normal flora
• Pathogenic
• Endospores

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The Viruses

• Non-cellular infectious agent
• Protein coat surrounding a nucleic acids core
• DNA or RNA
• Reproduce inside a host cell
• Enveloped or non-enveloped

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Viruses

• Shape
• Helical
• Polyhedral
• Enveloped or non-enveloped
• Spiked
• Complex
• Bacteriophages

Polyhedral Virus
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Viruses

• Bacteriophage
• Infects bacteria
• Used in early experiments to determine function
  of DNA

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Viruses

• Enveloped virus
• Envelope is made mostly of membrane remnents from
  previously infected cell
• HIV is example

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Infectious Agents Tinier Than Viruses

• Prions
• Proteins
• Altered products of a gene
• Diseases
• Kuru
• Scrapie
• Creutzfeldt-Jakob disease

• Viriods
• Tight folds of RNA
• Plant diseases

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Viral Multiplication Cycles

• 5 Steps
• Attachment
• Penetration
• Replication
• Assembly
• Release

• Lytic pathway
• Host cell lysis
• Lysogenic pathway
• Viral DNA integrates into bacterial chromosome

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Multiplication Cycle of a Bacteriophage
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Enveloped Virus Multiplication Cycle
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In Conclusion

• After the origin of life, a divergence occurred
  leading to Eubacteria and common ancestors of
  Archaebacteria and Eukaryotic cells
• All bacteria are prokaryotes
• Bacteria have 3 basic shapes cocci, bacilli, and
  spirilla

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In Conclusion

• Many bacteria have external structures that
  increase their survival and pathogenicity
• Bacteria reproduce by binary fission
• Many species have plasmids and some can transfer
  genetic information through the process of
  conjugation
• Bacteria as a group have metabolic diversity

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In Conclusion

• Viruses are nonliving infectious agents
• Viruses consist of either DNA or RNA surrounded
  by a protein coat
• Some may have an envelope and spikes
• Viruses cannot reproduce on their own but must
  use a host cells machinery
• There are five steps in the multiplication cycle
  of a virus

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In Conclusion

• There are two pathways common in the
  multiplication of bacteriophages lytic and
  lysogenic
• Multiplication cycles of viruses are diverse may
  occur rapidly or can enter a latent phase
• developed by M. Roig