Introduction
Bacteria belong to the Kingdom Prokaryotae (also known as Kingdom Monera) as their cells lack a nucleus. However, it has become increasingly clear that their are two distinct groups of prokaryotes which diverged from each other very early on in the course of evolution. Many researchers are already referring to these groups of bacteria as Domain Eubacteria and Domain Archaea (a domain is a taxonomic ranking above that of Kingdom). A third domain, Eukaryotae, has been proposed which would contain all other organisms with nucleated cells. Bacteria are both ancient and diverse; many have important ecological roles while comparatively few are pathogenic.

Table 1. Key differences between Prokaryotes and Eukaryotes

Feature	Prokaryotic cell	Eukaryotic cell
Nucleus	Absent. No nuclear envelope	Present with nuclear envelope and nucleolus
Membrane-bound organelles	Absent	Present. Includes mitochondria, chloroplasts (plants), lysosomes
Chromosome (DNA)	Single coiled chromosome in cytoplasm 'nucleoid' region in association with 'histone-like' proteins	Multiple linear chromosomes with histone proteins
Cell division (asexual)	No true mitotic apparatus. Divide by binary fission or fragmentation	Mitosis
Cell wall	Eubacteria have a cell wall of peptidoglycan Archaea have cell walls of pseudomurein	No cell walls in animal cells Plant cell walls = cellulose Fungal cell walls = chitin
Ribosomes	70S. Free in cytoplasm	80S. Both free in cytoplasm and attached to rough E.R. 70S in mitochondria and chloroplasts
Cytoskeleton	absent	present consisting of microtubules and filaments
Flagella	when present consist of protein flagellin	consist of 9+2 arrangement of microtubules
Cytoplasmic membrane lipids	Eubacteria= Fatty acids joined to glycerol by ester linkage Archaea= Hydrocarbons joined to glycerol by ether linkage	Fatty acids joined to glycerol by ester linkage

Prokaryotic Organisms:

I. Typical Characteristics of prokaryotes

• Lack a nuclear membrane
• Lack membrane-bounded organelles
• DNA is not associated with histones
• Cell walls made of peptidoglycan
• Divide by binary fission

• Bacterial size is measured in microns (um). Variations in size occurs but typically their size is 0.2 um in diameter and 8 um in length.
• Three basic celll shapes: coccus, bacillus, and spiral
• Cell arrangements are based on the patterns of division and whether the cell remain attached afterwards:
• Coccus:
•  diplococcus - pairs
• streptococcus - cocci occur in long chains
• staphylococci - irregular clusters
• Bacilli:
• diplobacillus, streptobacillus, coccobacillus
• Bacilli divide only across their short axis.
• Spiral:
• vibrios - one twist, comma shape
• spirillum (spirilla - plural) - corkscrew body very rigid
• spirochetes - flexible bodies.

• Glycocalyx / Capsule / Slime layer.
• Usually made of polysaccharide, and sometimes protein. Protect cell from animal defense mechanisms - avoid phagocytosis - very important with Streptococcuspneumoniae. Help bacteria to adhere to surfaces (Strep. mutants) and tissues. Source of nutrients. Protects against dehydration.
• Flagellum:
• Locomotion
• Structural protein is flagellin
• Three components: filament, hook and basal body
• Useful in taxonomy: mono (one), amphi (both), lopho (more than one in either side) and peritrichous (over entire cell)
• Many bacteria exhibit chemotaxis and phototaxis (can be positive or negative)
• Axial filaments:
• Present in spirochetes - often called endoflagellum
• Pili/Fimbria:
• Present in many Gram (-) cells - not involved in motility
• Fimbria - are short and allow cell attachment to surfaces
• Pili - long and used for conjugation (bacterial sex -bacterial DNA gets transferred from one bacterial cell to another).

• Determines shape of cell
• Protection from adverse conditions - Cell walls can be destroyed by antibiotics and enzymes - penicillin, cephalosporin, lysozyme.
• Made of Peptidoglycan - unique to Eubacteria
• Structural support - prevents the cell from bursting
• Site of action of some antibiotics
• Made of two sugars: n-acetylglucosamine (NAG) and n-acetylmuramic acid (NAM) and tetrapeptide amino acids.
• See the figures below or see page 79 in Tortora's.
• Bacteria can be divided into two large groups based on Gram stain:

        Gram positive - very thick cell walls. Layers and layers of peptidoglycan. Also contains teichoic acid and lipoteichoic acid.

Gram negative - very thin peptidoglycan layer in cell wall. Also has an outer membrane which is considered part of the cell wall. Outer membrane contains porins. The area between the peptidoglycan and cell membrane is called the periplasmic space.
Outer membrane - In Gram negative:

• Contains lipopolysaccharide (endotoxin)
• Acts as a barrier to penicillin, lysozyme, and digestive enzymes

• Atypical cell walls
• Acid fast bacteria - Have mycolic acid and wax D
• Mycobacterium tuberculosis
• Mycobacterium leprae
• No cell walls
• Mycoplasma
• L forms

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Several names are used: cell membrnane, plasma membrane or cytoplasmic membrane.

• 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 in what is known as the fluid mosaic model.
• Proteins are attached and inserted onto and into the phospholipid bilayer

 
• Functions
• Regulation of transport
• Enzymes for respiration
• Enzymes for energy generation
• Receptors for recognition, communication, attachment
• The cell membrane is a Selective permeable barrier

 

• Diffusion - movement of molecules from an area of high to an area of low concentration - equilibrium.
• Facilitated diffusion - requires a carrier protein present in the membrane
• Osmosis -  the diffusion of water (solvent) across a semipermeable membrane from high to low gradient concentration.
• Since the membrane is not permeable to the dissolved solutes inside the cell, water will move through the membrabe 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.
•  
Consequences of osmotic solutions:
1. Isotonic:
    [SOLUTE inside cell] = [SOLUTE outside cell]
    [WATER inside cell] = [WATER outside cell]
2. Hypotonic: Osmotic lysis (burst)
    [SOLUTE inside cell] > [SOLUTE outside cell]
    [WATER inside cell] < [WATER outside cell]
3. Hypertonic: Plasmolysis (shrink)
    [SOLUTE inside cell] < [SOLUTE outside cell]
    [WATER inside cell] > [WATER outside cell]

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• Requires energy - often ATP
• Two types: Active transport and Group translocation
• A receptor in the membrane binds the molecule to be transported.
• A conformational change in the receptor pushes the molecule tthrough the membrane and the molecule is released on the other side of the membrane (e.g. glucose and PEP).   

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• Matrix inside the plasma membrane
• 80% WATER
• Contains INCLUSIONS, RIBOSOMES, VACUOLES, NUCLEAR AREA. 

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Various small particles, crystals and bubbles

Polysaccharide (starch, glycogen)

Lipids

Sulfur

Gas

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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 (70S) compared with eukaryotic (80S)

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• Lack nuclear membrane
• Single chromosome, circular, double stranded DNA.

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 circunstances. But this information is not considered to be part of the genome.

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These are dormant (not metabolically active) bacterial cells.

Endospores are highly resistant to heat, drying, UV radiation, and chemical disinfectants.

Bacillus sp. and Clostridium sp. are the most important spore formers in medicine.

Germination VS sporulation?

Endospores are NOT reproductive structures as only one cell gives rise to one spore.

Endospores can be identified with special stains and differentiated from the vegetative cell.

During the process of sporulation, a copy of the DNA is pinched off into a separate part of the cell and the cell is protected with a heat-resistant calcified spore coat (dipicolinic acid).

The spore contains DNA, a small amount of RNA and little free water. Most metabolic activity shuts down

When conditions are favorable there is a rapid shift in metabolic activity and a return to the vegetative form of the cell

What is the difference between a vegetative cell and an endospore?

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