Bacteria

1
Bacteria
2
What are bacteria

• Prokaryotes
• Cell membrane is surrounded by a cell wall
• Chromosome is a single strand of DNA
• No mitochondria, chloroplasts, nuclear membrane

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Bacterial Structure

• Typical size 1-10 micromenter (10-100 micrometer
  for eukaryote cells)
• Single circular chromosome (DNA)
• Cell membrane made of protein and lipids
• Cell wall present
• Sometimes plasmids present

4
Bacterial Cell Wall

• Composed of complex carbohydrate and
  peptidoglycan
• Functions to regulate transport (molecules that
  flow in and out of the cell)
• Bacteria are identified based on their cell walls

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Hans Christian Gram and His Stain

• Cell walls with carbohydrate take up the stain
  that Gram invented
• These cells are purple under a light microscope
• They are called Gram-positive bacteria
• Cell walls with carbohydrate and lipids do not
  take up Grams stain
• These cells are not purple under a light
  microscope
• These are Gram-negative bacteria
• Infection with Gram-negative bacteria is usually
  very serious

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Structure and Function

• Cell classified by shape
• Bacillus (bacilli) are rod shaped
• Coccus (cocci) are spherical
• Spirillum (spirilli) are spiral shaped
• Nutrition and metabolism
• Energy capture (page 582)
• Metabolism (page 583)

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Two Kingdoms of Bacteria

• Eubacteria
• Archaebacteria
• Classification based on differences in ribosomal
  RNA

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Eubacteria

• Largest group of bacteria
• Found everywhere
• Diverse ecology and biochemistry
• Some are photosynthetic, free living in soil,
  parasitic

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Archaebacteria

• Ancient bacteria
• Live in extreme environments (extremeophiles)
• Many survive in the absence of oxygen
• Cells walls lack peptidoglycan

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Growth and Reproduction

• Binary Fission
• Conjugation
• Spore formation

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Binary Fission

• Cell doubles in size
• Chromosome replicates
• Cell splits into two identical daughter cells
• No exchange of genetic information
• This is asexual reproduction

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Conjugation

• Protein bridge forms between two cells
• Some DNA exchanged between the cells
• Cells incorporate the new DNA, chromosome
  replicates
• Cells divide
• This is a form of sexual reproduction

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Sporulation

• Form a structure called a spore when
  environmental conditions are adverse
• Spore encloses some cytoplasm and the DNA
• Spore resists heat, drying, desiccation,
  radiation, and chemical disinfectants
• Spore survives for years
• When conditions are better the spore hatches
  and the bacteria can grow again

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Bacteria and disease

• Pasteur found the link between bacteria and
  disease
• Strep throat, diphtheria, tuberculosis, typhoid,
  tetanus, syphilis, gonorrhea, cholera, lyme
  disease, bubonic plague, food poisoning, botulism

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Bacteria cause disease in two ways

• Attacking cells and tissues of the body directly,
  using cells and tissues for nutrients
• Producing toxins which in turn interfere with
  functions in the body
• Fighting disease
• Vaccination
• Antibiotics