Bacterial Structures


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NZQA Unit 8024 - Demonstrate knowledge of bacterial structures

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Bacterial Structures

  1. 1. Unit 8024 Demonstrate knowledge of Bacterial Structure By Elysia Butler
  2. 2. Cell Wall <ul><li>The cell wall of a gram negative bacteria (E.coli) is generally thinner than the cell wall of a gram positive bacteria ( S.aureus) </li></ul>
  3. 3. Gram Positive Structure Peptidoglycan Cell Wall Cytoplasm Cytoplasmic Membrane Cell Section Enlargement = Within the peptidoglycan stand are teichoic acids and polysaccharides
  4. 4. Gram Negative Structure Cell Wall Cytoplasm Cytoplasmic Membrane Peptidoglycan Outer Membrane Section Enlargement = Cell The outer membrane contains Porin trimers, O antigens and Lipopolysaccharides. There is also a space between the Cytoplasmic Membrane and the Outer Membrane which is known as the Periplasmic Space
  5. 5. Peptidoglycan <ul><li>The Peptidoglycan layer within a cell wall is made up of amino sugars; </li></ul><ul><li>NAG = N-acetylglucosamine </li></ul><ul><li>NAM = N acetylmuramic acid </li></ul><ul><li>Glycosidic bonds link the alternating sugars together. </li></ul><ul><li>Attached to each NAM is an amino acid chain. </li></ul>
  6. 6. Peptidoglycan Composition <ul><li>Gram Positive (Specific to S.aureus ) </li></ul><ul><li>Gram Negative (Specific to E.coli) </li></ul>L-alanine D-glutamine L-lysine D-alanine L-alanine D-glutamine L-lysine D-alanine Glycosidic Bond L-alanine D-glutamine Meso-Diaminopimelic acid D-alanine D-alanine D-glutamine L-alanine Glycosidic Bond Meso-Diaminopimelic acid NAM NAG NAM NAM NAM NAG NAG NAG
  7. 7. Lipopolysaccharide <ul><li>A Lipopolysaccharide is a Polysaccharide (complex Carbohydrate) joined to a lipid (fat) by the way of a covalent bond (electron sharing) </li></ul><ul><li>Only Gram negative bacteria contain Lipopolysaccharides. </li></ul><ul><li>Because of the Lipopolysaccharides, gram-negative bacteria are generally more toxic, more protected from their hosts defence systems, and more resistant to antibiotics than gram positive bacteria. </li></ul>
  8. 8. Gram Stain Steps <ul><li>Cells are heat fixed to a microscope slide and then stained to help determine whether a bacterium is either gram negative or gram positive. </li></ul><ul><li>Crystal Violet (a purple dye) is applied </li></ul><ul><li>Iodine (a mordant) to set the dye to the cell is applied </li></ul><ul><li>Ethanol (a decoloriser) is applied </li></ul><ul><li>Safranin (a counter stain) is applied </li></ul>
  9. 9. Gram Negative Stain <ul><li>Gram negative bacteria have an outer membrane containing lipids. </li></ul><ul><li>These lipids are dissolved by the ethanol </li></ul><ul><li>It is now easier for molecules to enter and exit the cell membrane. </li></ul><ul><li>This enables the crystal violet and iodine complex to be washed away. </li></ul>
  10. 10. Gram Negative Outcome <ul><li>Gram Negative bacterium will stain pink </li></ul><ul><li>To the left is a photograph of E.coli taken using a light microscope. </li></ul>
  11. 11. Gram Positive Stain <ul><li>Gram positive do not have a lipid containing outer membrane. </li></ul><ul><li>Therefore the ethanol can be directly absorbed by the peptidoglycan. </li></ul><ul><li>The ethanol causes the peptidoglycan to dry out and shrink. </li></ul><ul><li>This shrinking action traps the crystal violet and iodine complex </li></ul>Above is a theory of how the gram positive stain works
  12. 12. Gram Positive Outcome <ul><li>Gram Positive bacterium will stain purple </li></ul><ul><li>To the right is a photograph of S.aureus taken using a light microscope </li></ul>
  13. 13. Nucleic acid <ul><li>All bacteria contain nucleic acid (joined nucleotides) </li></ul><ul><li>DNA (deoxyribonucleic acid) is a type of nucleic acid. It is responsible for carrying all the hereditary material </li></ul><ul><li>DNA is made up of nucleotides </li></ul><ul><ul><li>A nitrogenous base </li></ul></ul><ul><ul><li>A pentose sugar </li></ul></ul><ul><ul><li>A phosphate group </li></ul></ul>
  14. 14. Cytoplasmic Membrane <ul><li>Made up of Proteins and Phospholipids </li></ul><ul><li>Polar ends face out </li></ul><ul><li>Non-polar ends face in </li></ul><ul><li>Controls what enters and exits the cell </li></ul>Cytoplasmic Membrane Polar end of Phospholipid Non-Polar end of Phospholipid Protein
  15. 15. Endospores <ul><li>Only present in some Gram-positive bacteria </li></ul><ul><li>Form when environmental conditions are un-favourable </li></ul><ul><li>For example </li></ul><ul><li>Lack of nutrients </li></ul><ul><li>Temperature change </li></ul>
  16. 16. Dormancy <ul><li>Predictive - When endospores form before environmental conditions become un-favourable </li></ul><ul><li>Consequential - When endospores form when conditions begin to become un-favourable </li></ul>
  17. 17. Endospore Resistance <ul><li>Resistant to heat, drying and some toxic chemicals eg some disinfectants </li></ul><ul><li>Gets rid of water when forming </li></ul><ul><li>Contains dipicolic acid which is not found in a vegetative cell </li></ul><ul><li>Is non-metabolic in this form </li></ul><ul><li>Formed through a process called sporulation </li></ul>
  18. 18. Endospore Diagram <ul><li>Cortex is thick peptidoglycan which removes water, may be a factor that leads to heat resistance </li></ul><ul><li>Spore coat is impermeable leading to chemical resistance </li></ul>Exosporium Spore Coat Cortex Cytoplasmic Membranne Nucleoid Note: Diagram is not drawn to scale