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Bacteria
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  • 1. Bacteria
  • 2.
    • Bacteria are prokaryotes.
    • Unlike animals and other eukaryotes, bacterial cells do not contain a nucleus or other membrane-bound organelles.
  • 3.
    • Bacterial cells are about 10 times smaller than eukaryotic cells and are typically 0.5–5.0 micrometers in length.
  • 4.
    • The study of bacteria is bacteriology, a branch of microbiology.
  • 5.
    • Bacteria are ubiquitous in every habitat on Earth, growing in soil, acidic hot springs, radioactive waste, seawater, and deep in the earth's crust.
  • 6.
    • Some bacteria can even survive in the extreme cold and vacuum of outer space.
    • There are typically 40 million bacterial cells in a gram of soil and a million bacterial cells in a milliliter of fresh water.
  • 7.
    • Bacteria are vital in recycling nutrients, and many important steps in nutrient cycles depend on bacteria, such as the fixation of nitrogen from the atmosphere.
    • There are approximately 10 times as many bacterial cells as human cells in the human body, with large numbers of bacteria on the skin and in the digestive tract.
  • 8.
    • Pathogenic bacteria cause infectious diseases, including cholera, tuberculosis, anthrax and bubonic plague.
    • The most common fatal bacterial diseases are respiratory infections, with tuberculosis alone killing about 2 million people a year, mostly in sub-Saharan Africa.
  • 9. Bacterial Shape Most bacterial species are either spherical, called cocci or rod-shaped, called bacilli.
  • 10. Bacterial Shape
    • Some rod-shaped bacteria, called vibrio, are slightly curved or comma-shaped.
    • Others, can be spiral-shaped, called spirilla, or tightly coiled, called spirochetes.
  • 11.
    • Like all living organisms, bacteria contain ribosomes for the production of proteins, but the structure of the bacterial ribosome is different from those of eukaryotes.
    • Around the outside of the cell membrane is the bacterial cell wall.
    • Bacterial cell wall is made of peptidoglycan.
    • The bacterial cell is surrounded by a lipid membrane or cell membrane.
    • They lack mitochondria, chloroplasts and the other organelles present in eukaryotic cells, such as the Golgi apparatus and endoplasmic reticulum.
  • 12. Nucleoid (Bacterial Chromosome)
    • Since the bacterial cell is prokaryotic, a true nucleus is absent.
    • The nuclear material is represented by DNA which is not associated with histones.
    • The bacterial DNA is circular and is attached at a point to the plasma membrane.
  • 13. Plasmid
    • Plasmids are extra chromosomal DNA molecules found in bacterial cells.
    • The plasmid DNA replicates independently.
    • It has certain genes like fertility factor (F-factor), resistance factor (R-factor) and nitrogen fixing genes (Nif-genes).
  • 14. Mesosomes
    • Mesosomes are infoldings of plasma membrane found in some bacterial cells.
    • It contains enzymes for performing respiration and pigments for photosynthesis.
  • 15. Food Granules
    • Food stores are common in the cytoplasm of many bacteria.
    • They occur as small granules of lipid or glycogen held in sacs formed from lipid membrane.
  • 16.
    • Flagella are rigid protein structures, that are used for motility.
    • Pili are cellular appendages, that can transfer genetic material between bacterial cells in a process called conjugation.
    • They are used for attaching to the host surface.
  • 17. Capsule (Slime Layer)
    • Thick polysaccharide layer outside of the cell wall.
    • It is used for:
      • Sticking cells together
      • As a food reserve
      • As protection against desiccation (drying out) and chemicals, and as protection against phagocytosis (being broken down by a white blood cell).
  • 18. Types of Bacteria
    • There are two different types of cell wall in bacteria, called Gram-positive and Gram-negative.
    • The names originate from the reaction of cells to the Gram stain, a test used for observing bacteria.
  • 19. Types of Bacteria
    • Gram positive bacteria have a thick cell wall and stain purple
    • Gram negative bacteria have a thin cell wall with an outer lipid layer and stain pink.
  • 20.
    • Gram-positive bacteria possess a thick cell wall containing many layers of peptidoglycan and teichoic acids.
    • In contrast, Gram-negative bacteria have a relatively thin cell wall consisting of a few layers of peptidoglycan surrounded by a second lipid membrane containing lipo-polysaccharides and lipoproteins.
    • Most bacteria have the Gram-negative cell wall.
  • 21. Reproduction
  • 22. Binary Fission
    • It is the most common mode of asexual reproduction.
    • The cytoplasm and nucleoid of a bacterial cell divide equally into two, following replication of DNA.
    • The cell wall and cytoplasm also split resulting in the formation of two daughter cells.
  • 23. Sexual Reproduction
    • In bacterial sexual reproduction there is no meiosis, formation of gametes and zygote.
    • Instead, it involves transfer of a portion of genetic material (DNA) from a donor cell to a recipient cell.
    • This process is called as genetic recombination
    • It is known to occur in the following three ways.
      • Transformation
      • Transduction
      • Conjugation
  • 24. Transformation
    • Many bacteria can acquire new genes by taking up DNA molecules from their surroundings.
  • 25. Transduction
    • Transduction is the process by which bacterial DNA is moved from one bacterium to another by a virus.
  • 26. Conjugation
    • Some bacteria can transfer a portion of their chromosome to a recipient with which they are in direct contact.
    • As the donor replicates its chromosome, the copy is injected into the recipient.
    • At any time that the donor and recipient become separated, the transfer of genes stops.
  • 27. Endospores (Spores)
    • Some bacterial cells tide over unfavorable conditions by forming endospores.
    • During this process, a portion of the cytoplasm and a copy of the bacterial chromosome undergo dehydration and get surrounded by a three-layered covering.
    • The resulting structure, called endospore can tolerate extreme environmental conditions and can remain viable for several years.
    • When the environmental conditions are suitable, the endospore absorbs water, swells and the wall splits, releasing the cell inside. It develops a new cell wall and starts functioning as a typical bacterial cell.
  • 28. Endospore formation