MICROBIOLOGY 130

PROCARYOTES

Look at "typical" bacterial cell - pg. 80 Tortora et. al. 7th ed


A. Cell wall

Made of peptidoglycan - unique to the eubacteria
See page 87 Tortora et.al., 7th ed. - notice the sugars joined to the peptides (small proteins, short chains of amino acids.)
 
Bacteria can be divided into two large groups based on gram stain:
 
See Tortora et. al., 7th ed. - pg. 89 for a description of the biochemical differences between g(+) and g(-) bacteria.
  
Function Of The Bacterial Cell Wall
 
Shape - See Pages 78 and 79, Tortora et.al., 7th ed
 
Protection from adverse conditions
Cell walls can be destroyed by antibiotics and enzymes :
 
Atypical cell walls
Acid fast bacteria
Have wax D and mycolic acid
    • Mycobacterium tuberculosis
    • Mycobacterium leprae
 
No cell walls
Mycoplasma
 

B. Cell membrane - plasma membrane - cytoplasmic membrane

- see pages 43 - 44 and 91, Tortora et.al., 7th ed.

 

Made up of phospholipids
Discuss structure of these molecules with regard to hydrophilic / polar head groups and hydrophobic hydrocarbon chains
 
Phospholipids Are Arranged In A Bilayer
 
Proteins are attached and inserted onto and into the phospholipid bilayer. (fluid mosaic model)
    • Enzymes for reactions
    • Pores for diffusion processes (diffusion and facilitated diffusion)
    • Receptors for transport
    • Receptors for recognition, communication, attachment
 
The cell membrane is a selectively permeable barrier
 
Movement across the membrane:
1. Diffusion and facilitated diffusion are covered on page 92 -94, Tortora et.al., 7th ed.
Remember that this is a passive process where a solute moves from high concentration to low concentration.
(what is a solute? What is a solvent?)
 
2. Osmosis is a special case of diffusion:
The diffusion of water (solvent) across a membrane which is impermeable to solute yet permeable to water. (a semi-permeable membrane). See page 94, Tortora et.al., 7th ed.
It may be helpful to remember that when solute dissolves, the free water concentration decreases.
If a cell is placed in pure water, the free water concentration is greater outside the cell.
Since the membrane is not permeable to the dissolved solutes inside the cell, water will move through the membrane into the cell.
As this happens cell volume will increase, eventually surpassing the strength and limits of the cell membrane and the cell will lyse.
 

Isotonic:
[solute inside cell] = [solute outside cell]
[water inside cell] = [water outside cell]
 

Hypotonic: osmotic lysis
[solute inside cell] > [solute outside cell]
[water inside cell] < [water outside cell]
 

Hypertonic: plasmolysis
[solute inside cell] < [solute outside cell]
[water inside cell] > [water outside cell]
 



3. Active transport
    • Requires energy - often ATP
    • A receptor in the membrane binds the molecule to be transported.
    • A conformational change in the receptor pushes the molecule through the membrane and the molecule is released on the other side of the membrane.
 

4. Phagocytosis / pinocytosis/ endocytosis
This is a specialized membrane transport mechanism found in eucaryotes.
(describe this and membrane fusion.)
 

Outer membrane - in gram negatives (see page 87, Tortora et.al., 7th ed).
    • Contains endotoxin - lipopolysaccharide
    • Helps void the defense mechanisms of the body
    • Induces a strong fever response
    • Causes a drop in blood pressure and shock
    • Acts as a barrier to penicillin, lysozyme and digestive enzymes
    • Provokes the release of abnormally high levels of cytokines
      • cytokines are proteins released by WBC's which influence the activities of other cells. In this case interleukin-1 (IL-1) and tumor necrosis factor (TNF) and interferon-g (IFN-g ) are the most important.
      • chemokines are proteins released by cells which influence the movement and migration of WBC's.
 



C. Glycocalyx / capsule / slime layer / extracellular polymeric substance / EPS

    • Usually made of polysaccharide sometimes protein
    • Protects cell from animal defense mechanisms - avoid phagocytosis - very important with streptococcus pneumoniae.
    • Helps bacteria to adhere to surfaces and tissues
    • Maybe food storage
    • Protects against dehydration
 



D. Flagella - see pages 82 - 84, Tortora et.al., 7th ed

    • Like little propellers
    • Main structural protein is flagellin
    • Many bacteria exhibit chemotaxis and phototaxis, (can be positive or negative).
    • These are sometimes called H-antigens. (Distinguish this from O-antigens.)



E. Axial filaments - see page 84, Tortora et.al., 7th ed

    • Treponema
    • Leptospira
    • Borrelia

 



F. Fimbriae / pili /sex pili

    • Can be used for attachment to surfaces (adhesin)
      • E. coli, type P pili -- seen in pyelonephritis
      • E. coli, type 1 pili -- seen in cystitis
      • also M protein on Streptococcus pyogenes
      • Specialized ones are used for conjugation (bacterial sex),
These are called sex pili.
Bacterial DNA gets transferred from one bacterial cell to another during conjugation.
 

G. Cytoplasm / cytosol

Matrix inside the plasma membrane
80% water
Contains inclusions, ribosomes, vacuoles, nuclear area.



H. Inclusions

    • Various small particles, crystals and bubbles
    • Polysaccharide (starch, glycogen)
    • Lipids
    • Sulfur
    • Gas
    • Magnitite

I. Ribosomes - see page 96, Tortora et.al., 7th ed

    • Particles made up of two subunits (30s and 50s)
    • Subunits are made up of RNA and protein
    • Proteins are made on ribosomes
    • Procaryotic ribosomes are small ribosomes

J. Nuclear area / nucleoid - see pages 212 and 80

The bacterial chromosome - the bacterial genome
    • All the information needed to make and reproduce a bacterial cell of a particular species. All the essential information of that species.
    • Circular, double stranded DNA
    • A bacterial cell may have more than one chromosome but these are duplcates and only one is needed.
Plasmids
    • Small, circular double stranded pieces of DNA.
    • These are transferred very easily through conjugation.
    • The information on plasmids is often useful to the bacterium. It may even be vital for survival under certain circumstances. But this info is not considered to be part of the genome of the cell.

K. Endospores - see page 97 - 98

    • These are dormant (not metabolically active) bacterial cells.
    • Endospores are highly resistant to heat, drying, and chemical disinfectants
    • Bacillus sp. And Clostridium sp. Are the most important spore formers in medicine.
      • Anthrax
      • Tetanus
      • Botulism
What is the difference between a vegetative cell and an endospore?