TR

Bacteria

Genetic Properties of Bacteria

  • Bacterial chromosome: where genes of bacteria are found
  • Usually a single type of chromosome
  • May have more than one copy of that chromosome
  • Number of copies depends on the bacterial species and on growth conditions
  • Typically 1-4 identical chromosomes
  • Nucleoid: region where tightly packed bacterial chromosome found

Bacterial Chromosomes

  • Molecules of double-stranded DNA
  • Usually circular
  • Tend to be shorter
  • Contains a few thousand unique genes
  • Mostly structural genes
  • Single origin of replication

Plasmids

  • Plasmids: small, circular pieces of DNA that exist independently of the bacterial chromosome
  • Occur naturally in many strains of bacteria and in \n a few types of eukaryotic cells, such as yeast
  • Own origin of replication that allows it to be replicated independently of the bacterial chromosome
  • Not usually necessary for survival but can provide growth advantages
  • Episome: plasmid that can integrate into bacterial chromosome

Five Types of Plasmids

  1. Resistance plasmids (R factors): confer resistance against antibiotics and other types of toxins
  2. Degradative plasmids: enable the bacterium to digest and utilize an unusual substance
  3. Col-plasmids: encode colicines, which are proteins that kill other bacteria
  4. Virulence plasmids: turn a bacterium into a pathogenic strain
  5. Fertility plasmids (F factors): allow a bacteria to mate

Reproduction

  • Some species like E. coli can divide every 20-30 minutes
  • Single cell can form a bacterial colony in less than a day
  • Reproduce by  binary fission - NOT mitosis
  • Unless a mutation occurs, each daughter cell contains \n an identical copy of the mother cell’s genetic material
  • Does not involve genetic contributions from two different parents
  • Plasmids may replicate independently of the bacterial chromosome

Bacteria Structure

  • A cytoplasmic membrane
    • surrounded by a peptidoglycan cell wall
    • may have an outer membrane
  • A fluid cytoplasm containing
    • nuclear region (nulceoid)
    • ribosomes
  • External structures such as pili, glycocalyx, and flagella
  • 3 shapes of bacteria are coccus, bacillus, and spiral

The Bacterial Cell Wall

  • Protection from osmotic lysis
  • Provides shape to the bacteria
  • In direct contact with the environment
  • Pathogenesis
  • Cell walls contain peptidoglycan cross-linked by polypeptides

Ribosomes, Inclusions, and Endospores

  • Ribosomes: consist of RNA plus protein: sites of protein synthesis
  • Inclusions: aggregates of various compounds that are normally involved in storing energy reserves or building blocks for the cell.
  • Endospores are resistant to 
    • High temperatures (including boiling)
    • Most disinfectants, low energy radiation, drying
    • The endospore can survive thousands of years until some environmental stimulus triggers germination

Bacterial Flagella

  • Usually found on bacilli and some spirals
  • Composed of flagellin
  • Involved in locomotion
  • Allows bacteria to respond to specific stimuli
    • Chemotaxis
    • Magnetotaxis

Glycocalyx

  • Functions include
    • Attachment to surfaces
    • Protection from desiccation
    • Nutrient trap
    • Protection from phagocytosis
    • Protection from certain toxins
    • Detergents