Bacteria and Viruses

1
Bacteria and Viruses

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

2
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
6
Prokaryotic Fission
7
Prokaryotic Fission
8
Prokaryotic Fission
9
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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viral RNA
protein subunits of coat
18-nm diameter, 250-nm length
80-nm diameter
lipid envelope proteins span the envelope, line
its inner surface, and spike out above it
DNA
protein coat
sheath
viral RNA
base plate
tail fiber
reverse transcriptase
viral coat (proteins)
65-nm diameter head, 225-nm total length
100-120 nm diameter
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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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4 virus particle
7.6 µm
4 virus particle
300 µm
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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