Bacteria

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Bacteria

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

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