Session 3 - Cell Structure & Function

• Morphology deals with the shape, size, and arrangement of living organism.
• Cellular morphology is the study of size and shape of the cell.
• A typical bacterium is <3 micrometer in size.
• Bacterial Shapes

  • Coccus - spherical and ovoid
  • Bacillus - cylindrical / rod-shaped
  • Spiral - curve or loose spiral
• Spirochetes


  refers to the tightly coiled spiral bacteria.
• Bacterial arrangement

  • singly - singular
  • strepto - comes in chain
  • staphylo - comes in cluster
  • diplo - in pairs
  • sarcinae - three-dimensional cubes
• bacterial arrangement that comes in four

  tetrad
• Pleomorphic


  no definite shape and/or arrangement
• Prokaryotic Cell - simplest and earliest form of cell in the earth; falls under domain Bacteria and domain Archaea.
• Bacterial membrane


  a phospholipid bilayer containing embedded proteins.
• Bacterial membrane is composed of hydrophobic tails (fatty acid)and hydrophilic head (glycerol molecule, containing phosphate).
• Hopanoids


  these are sterol-like molecules / compounds present in bacterial membrane.
• Cell membrane


  also known as cytoplasmic membrane.
• Cell membrane


  It is the gatekeeper for the entrance and exit of dissolved substances.
• Cell membrane has three (3) major functions:

  (1) Selective permeability

  (2) Anchorage

  (3) Energy conservation and consumption - that takes place in the mitochondrion and chloroplast
• Differences in Cytoplasmic Membrane of (a) Bacteria & Eukarya and (b) Archaea:

  • Structure: (a & b) It has the same structure.
  • Lipid Layer: (a) Lipid Bilayer & (b) Lipid Monolayer
  • Chemical Structure: (a) Ester linkages bond fatty acids to glycerol & (b) Ether bonds between glycerol and a hydrophobic side
  • Hopanoids: (a) Present & (b) Absent.
• Cell wall


  layer outside the cytoplasmic membrane.
• Four (4) major functions of a cell wall:

  1. Gives shape and rigidity on the cell.
  2. Confers structural strength on the cell to keep it from bursting due to osmotic pressure.
  3. Contributes to pathogenicity.
  4. Site of action of several antibiotics.
• Parts of Prokaryotic Cell

  a - Capsule

  b - Cell wall

  c - Cell membrane

  d - fimbriae

  e - flagella

  f - plasmid

  g - chromosome

  h - ribosomes

  i -cytoplasm

  j - inclusions

  
• Bacterial cell wall have distinct components including (1) lysozymes, (2) peptidoglycan, (3) periplasm, and (4) porins.
• Lysozyme

  • weakens the peptidoglycan and cause cell lysis.
  • act as a major line of defense against bacterial infection which are present in human secretions including tears, saliva, and other bodily fluids.
  • destroys pre-existing peptidoglycan, penicillin blocks a key step in its biosynthesis.
• Peptidoglycan


  Made up of rigid polysaccharide; not present in Archaea and Eukarya.
• Peptidoglycan is composed of alternating repeats of two modified glucose residues such as: (a) N-acetylglucosamine and (b) N-acetylmuramic acid
• 90% of cell wall in a Gram positive bacteria consist of peptidoglycan and form many layers.
• Teichoic acid


  embedded in the cell wall and function to bind divalent metal ions, such as Ca2+ and Mg2+, prior to their transport in the cell.
• Lipoteichoic acid


  covalently bonded to membrane lipids rather than to peptidoglycan.
• lipopolysaccharide


  small amount of peptidoglycan in cell wall of Gram negative.
• Periplasm


  The space located between the outer surface of the cytoplasmic membrane and the inner surface of the outer membrane; spans about 15 nm.
• Porins 


  Channels for the entrance and exit of solutes. It has two types which are non-specific and specific.
• Pseudomurein = peptidoglycan (Archaea)
• S-Layer


  Paracrystalline surfance layer in Archael cell wall.
• Cell Surface Structures


  Also called as outer surface layers.
• Cell surface structures have specialized functions that plays a significant role in:

  (1) Attachment

  (2) Virulence factors

  (3) Preventing dehydration
• Types of cell surface structures:

  • Glycocalyx
  • Fimbriae
  • Pili
  • Hami / Hamus
• Capsule


  Organized in a tight matrix that excludes small particles and is tightly attached; readily visible by light microscopy.
• Slime


  More easily deformed and loosely attached. It will not exclude particles; more difficult to see microscopically.
• Bacillus anthracis is capsule-forming whereas Staphylococcus pneumoniae is slime-forming.
• Fimbriae

  • Thin filamentous structures made of protein that extend from the surface of a cell
  • 2-10 nm in diameter
  • Enable cells to stick to surfaces
  • Form pellicles or biofilms on solid surfaces
• Pili

  Typically longer and only one or a few pili are present on the surface of a cell

  All Gram negative produce pili while many Gram positive contain pili

  Can be receptors for certain types of viruses, they can be easily seen under the electron microscope when they become coated with virus particles
• Functions of Pili: (1) Adhesion and (2) Conjugation