Ohne Titel

Bacteria cell structure and function

1. Cell Wall

   • N-acetylmuramic acid and N-acetylglucosamine glycan backbone and peptide side chains L-alanine, D-alanine, D-glutomic acid, and diaminopimelic acid
   • Gram negative bacteria have direct peptide link between the peptide side chains, whilst gram positive bacteria have an interbridge made of peptide
   • Glycosidic bonds (bonds between molecules in the glycan backbone) give lateral strength whilst peptide bonds bind vertical strength.
   • Gram positive cell walls contain teichnoic acid and lipotechnoic acid (teichnoic acid + lipids)

2. Gram staining

   • Gram positive stain purple/blue and gram negative stain red/pink
   • Mycobacteria are gram positive bacteria but the mycolic acid in their walls give them a waxy texture which resist gram stain. Acid-fast stain is used instead.
   • Crystal violet, iodine, alcohol, safranin

3. Archaea

   • Have no peptidoglycan. Their walls are made of an 'S' layer - a ridgid layer of proteins.
   • Phospholipid monolayer.

4. Cell structure

   • Phospholipid bilayer 6nm thick
   • No organelles in the cytosol. Cytosol does contain a copy of DNA circular chromosme plus plasmids. Also inclusions or endospores.
   • An inclusion is a storage mechanism for glycogen and lipids

5. Endospores

   • They are formed when there is a lack in nutrients and allow bacteria to lie dormant. They are reactivated when the environment becomes more favourable.
   • The bacteria divides within its cell and then one side engulfs the other. It then forms a cortex of calcium and diplolinic acid and a spore coat which gives it a high level of protection.
   • 1. DNA replicates. 2. Cell divides within the cell. 3. One side is digested by the other. 4. Cortex forms around surviving half of the cell. 5. Spore coat forms around the cortex. 6. Endospore is released from the original cell.

6. Fimbria and pili

   • Fimbria are used for attachment to other cells. There can be up to 1000 on one bacteria.
   • Pili are used for conjugation.

7. Capsule and slime layer

   • A capsules (or glycocalyx) are firmly attached, slime layers are loose and can be removed.
   • Protective function.

8. Flagella

   • Polar flagellation - the flagella is attached at one or both ends of the cell.
   • Laphotrichous flagellation - the bacteria has multiple flagella ocated at the same place, moving the bacteria in one direction only.
   • Peritrichous bacteria - "tumble and run" - bacteria has flagella projecting in all directions.