MBY L1-Microbial Cell Structure and Function

• Microbial Cell Structure and Function

  Cytoplasmic membrane and wall, Cell surface structures and functions, Inclusion bodies, Microbial locomotion

  
• Cytoplasmic membrane (bacteria)


  • Also known as plasma membrane
  • Specialized structure that surrounds the cell and its internal environment
  • Controls the movement of substances into/out of the cell
  • Small ions cannot freely pass due to their charges
  • Fluid nature (constantly in motion) - fluid mosaic model
  • Allows for lateral movement of phospholipids and proteins
  • Serves as a gateway for transporting nutrients into & waste out of the cell
  • Can be energized - Proton motive force (PMF) and ATP (ATP synthase)
• Cytoplasmic membrane (bacteria)


  • Phospholipid bilayer
  • Integral proteins, Monotopic proteins, Peripheral proteins

  
• Cytoplasmic membrane (archaea)


  • Basic structural properties same as bacteria
  • Contain ether linkages between the glycerol and a hydrophobic side chain
  • Membranes are composed of carbon isoprene units that combine to form phytanyl side chains
  • Glycerol diether known as Archaeol
  • Provides superior thermostability of the membrane, commonly found in hyperthermophilic archaeal species

  
• Bacterial cell wall


  • Provides overall strength to the cell
  • Helps maintain the cell shape and rigidity
  • Protects cells against osmotic lysis

  
• Bacterial peptidoglycan


  • Glycosidic bonds are β-1,4
  • Composed of glycan tetrapeptide - two amino sugars (G & M) and a tetrapeptide attached to M
  • Cross-linkers in Gram-negative bacteria and interridge in Gram-positive bacteria

  
• Cell envelope


  • Comprises the inner cell membrane and the cell wall of a bacterium
  • In gram-negative bacteria an outer membrane is also included
  • Archaea have an S-layer - proteins and or glycoproteins that prevent osmotic lysis

  
• Archaea cell envelope


  • Contain a polysaccharide called pseudomurein
  • N-acetylglucosamine (G) and N-acetyltalosaminuronic acid (T)
  • Glycosidic bonds are β-1,3
  • Amino acids are of the L stereoisomer

  
• Bacterial outer membrane


  • Represents a second lipid bilayer of the cell
  • Contains polysaccharides linked to lipids - lipopolysaccharides (LPS)
  • LPS has three covalently liked regions
  • Periplasm is between outer and cell membrane and houses periplasmic proteins

  
• Porins in outer membrane
• Surface polysaccharides


  • Sticky or slimy materials on their cell surface that consist of either polysaccharides or proteins
  • Protect the cell from attack and environmental stresses, such as desiccation
  • Do not confuse slime layers with surface (S)-layers
• Cell inclusions


  • Function as energy reserves and or carbon reservoirs or have special functions
  • Synthesized by cells when there is an excess of organic and inorganic compounds
  • Inorganic and organic cell inclusions
  • Enclosed in a thin membrane and partitioned in a cytoplasm or periplasm
• Cell inclusions


  • Polyphosphate, Sulfur, and Carbonate Minerals
  • Magnetic storage inclusions (Magnetosomes)
  • Poly-b-hydroxybutyric acid (PhB)
  • Glycogen
  • Gas vesicles

  
• Flagella and flagellation


  • Long and thin appendages ~15–20 nm wide
  • Arranged in a variety of ways on the cell surface
  • Rotate to propel the cell
  • Direction of the rotation - forward, backward, or tumbles in place
  • Requires significant energy directly from a proton motive force
• Flagella structure (bacteria)


  • Flagellin - principal component of bacterial flagella, forms the filament
  • Hook - connects the filament to the flagellum motor in the base
  • Flagellum motor - rotating machine anchored in the cell membrane and cell wall
  • L (outer) ring, P ring, MS and C rings
• Flagella structure (archaea)


  • Flagella and archaella are functionally similar
  • Motors are powered in fundamentally different ways - rotation of the archaellum is driven by the hydrolysis of ATP
  • Archaellum have small diameter compared to the flagellum
  • Several different proteins make up the filament
  • Archaellum considered a rotating type IV pilus capable of both clockwise and counterclockwise rotation
• Surface motility