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Chapter 4

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Prokaryote
comes from the Greek words for prenucleus.
One circular chromosome, not in a membrane
No histones
No organelles
Peptidoglycan cell walls
Binary fission
EX:
Staphylococcus
.. E. coli
Eukaryote
comes from the Greek words for true nucleus.
Paired chromosomes, in nuclear membrane
Histones
Organelles
Polysaccharide cell walls
Mitotic spindle
EX:
1)Amoeba
2)Paramecium
Size of Bacteria
0.2 -2.0 μm 2 - 8 μm
Bacillus
(rod-shaped)
Coccus
(spherical)
Spiral
Spirillum
Vibrio
Spirochete
Arrangement of cocci:
based on plane of division.
a) One plane,
b) two planes,
c) three planes, and
d) multiple planes
Arrangement of Bacilli
Single bacilli are most common, however, some bacilli remain attached to each other forming chains.
Arrangement of Spiral bacteria
-Curved rods
- Helical and rigid body
- Helical and flexible body
Unusual shapes of Bacteria
Star-shaped Stella (a)
Square Haloarcula (b)
Most bacteria are
monomorphic. A few are pleomorphic (e,g. Rhizobium and Corynebacterium)
Pairs:
Diplococci, diplobacilli
Clusters:
Staphylococci
Chains:
Streptococci, streptobacilli
Glycocalyx:
a network of polysaccharides on the surface of a bacterium
Is formed outside cell wall
Usually sticky
Such extracellular polysaccharide allows cell to attach
A capsule
-is neatly organized
-prevent phagocytosis of
>Bacillus anthracis
>Streptococcus pneumoniae
>Klebsiella pneumoniae
-supports attachment of: Streptococcus mutans
A slime layer
is unorganized and loose
Flagella
Long filamentous appendages that propel bacteria
Outside cell wall
Made of chains of flagellin
Attached to a protein hook
Anchored to the cell wall and membrane by the basal body
Motile Cells
rotate flagella to move ("run" or tumble)
The direction of flagella rotation determines which of
these movements will occur
Importance of Motile Cells
Movement toward or away from stimuli (taxis)
Flagella proteins are H antigens
Axial Filaments
an endoflagella consisting of a bundle of fibrils
Found in spirochetes
Anchored at one end of a cell
Rotation causes cell to move in a spiral motion
Many Gram negative bacteria contain
hairlike appendages that are shorter, thinner and
straighter than flagella - fimbriae
Fimbriae
allow attachment
Pili
are used to transfer DNA from one cell to another
- Unlike fimbriae that can be numerous at the poles or evenly distributed all over the cell surface, pili number one or two per cell
Cell Wall
A complex semirigid structure
>responsible for cell shape.
> Prevents osmotic lysis
Made of peptidoglycan (in bacteria)
Peptidoglycan
Polymer of disaccharide
>N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM)
Linked by polypeptides
Gram-Positive Cell Walls
Thick peptidoglycan
Teichoic acids
No outer membrane
In acid-fast cells, contains mycolic acid
Teichoic acids: consist primarily of an alcohol (glycerol
or ribitol) and phosphate
>Lipoteichoic acid links to plasma membrane
>Wall teichoic acid links to peptidoglycan
Importance
> May regulate movement of cations.
> Polysaccharides provide antigenic variation.
Gram-Negative Cell Walls
Thin peptidoglycan
No teichoic acids
Outer membrane
Gram-Negative Outer Membrane
Consists of lipopolysaccharides, lipoproteins, phospholipids
Forms the periplasm between the outer membrane and the plasma membrane.
Protects cells from phagocytes, complement, and antibiotics
Contain O polysaccharide, an antigen, e.g., E. coli O157:H7
Contain Lipid A, an endotoxin
Contain Porins, proteins that form channels through
membrane.
Gram Positive Stain Mechanism
Crystal violet-iodine crystals form in cell.
Alcohol dehydrates peptidoglycan
- but no holes in peptidoglycan
CV-I crystals do not wash out
Gram Negative Stain Mechanism
Alcohol dissolves outer membrane
>leaves holes in peptidoglycan.
CV-I washes out
Mycoplasmas
(smallest bacteria and pass through filters)
Lack cell walls
Contain sterols in plasma membrane
Sterol
thought to help protect cell lysis (rupture)
Archaea
Lack peptidoglycan cell wall (wall-less)
- or
have walls of pseudomurein
-Similar to peptidoglycan but differs as follows:
> Contains N-acetyltalosaminuronic acid instead of NAM
> D amino acids found in bacterial cell walls
Atypical Cell Walls (Acid-fast cell walls)
Like gram-positive, however
- Waxy lipid (mycolic acid) bound to peptidoglycan
Mycobacterium
Nocardia
Lysozyme
digests the disaccharide in peptidoglycan.
Penicillin
inhibits formation of peptide bridges in peptidoglycan.
Protoplast
is a wall-less Gram positive bacterium or plant cell
L forms are wall-less cells
that swell into irregular shapes.(Named for the Lister institute where they were discovered)
Spheroplast
is a wall-less Gram-negative cell.
Protoplasts and Spheroplasts
are susceptible to osmotic lysis.
Plasma Membrane
Consists of:
-Phospholipid bilayer
-Peripheral proteins
-Integral proteins (inside)
-Transmembrane proteins (integral proteins that
penetrate membrane completely)
Fluid Mosaic Model of Membrane Structure
Is the dynamic arrangement of proteins and phospholipids
- Membrane is as viscous as olive oil.
>Proteins move to function.
> Phospholipids rotate
and move laterally.
- Viscous nature ensures
> movement does not
destroy membrane.
Plasma Membrane
Selectively permeable
- allows passage of some molecules
Contain enzymes for ATP production
Contain photosynthetic pigments on foldings (plasma
membrane folds) called chromatophores or thylakoids
Damage to Plasma Membrane
Can be damaged by:
- alcohols,
- quaternary ammonium (detergents),
- polymyxin antibiotics
>Consequence
---- leakage of cell contents.
Simple diffusion:
Movement of a solute from an area
of high concentration to an area of low concentration.
Facilitative diffusion:
Solute combines with a
transporter protein in the membrane.
Osmosis:
The movement of water across a selectively
permeable membrane from an area of high water
concentration to an area of lower water.
Osmotic pressure:
The pressure needed to stop the movement of water across the membrane.
Active transport
of substances requires a transporter protein and ATP.
Group translocation
of substances requires a transporter protein and high energy supplied by high energy compound, phosphoenolpyruvic acid (PEP).
The substance is modified in the process
>Example by phosphorylation
---make it not possible to be transported out
---Example is transport of glucose
Cytoplasm
is the substance inside the plasma membrane.
Nuclear area (nucleoid) - consists of:
Long, continuous, circular thread of double-stranded
DNA (bacterial chromosome)
Carries genetic information
lacks cell membrane (unlike eukaryotic chromosome).
Ribosomes
-- Function as the site for protein synthesis. The cytoplasm of prokaryotic cell contains tens of thousands of these small structures which gives the cytoplasm a granular appearance
--Contrarily, eukaryotic ribosomes are 80s, which is divided into 60s for the large, and 40s for the small subunit.
S in 30s, 50s, 70s is
Svedberg units and refers to the relative rate of sedimentation during ultra-high speed centrifugation. Sedimentation rate is a function of the size, weight and shape of a particle.
Streptomycin and gentamycin
attach to the 30s
while chloroamphenicol and erythromycin attach to the 50s subunit inhibiting protein synthesis. Some antibiotics work by inhibiting protein synthesis on prokaryotic ribosomes.
Eukaryotic Ribosomes
Protein synthesis
80S
>Membrane-bound: Attached to ER
> Free: In cytoplasm
70S
> In chloroplasts and mitochondria
Endospores
are specialized "resting cells" or structures formed inside certain gram-positive bacterial cells
When essential nutrients are depleted
Endospores are resistant to desication, heat, chemicals
Bacillus, Clostridium form endospores -can be located terminally (at one end), subterminally (near one end) and centrally in the vegetative cell
Sporulation
is endospore formation
Germination
is return to vegetative state
Metachromatic granules (volutin)
Phosphate reserves
Polysaccharide granules
Energy reserves
Lipid inclusions
Energy reserves
Sulfur granules
Energy reserves
Carboxysomes
Contain ribulose 1,5-diphosphate carboxylase for CO2 fixation
Gas vacuoles
Protein covered cylinders (buoyancy)
Magnetosomes
Iron oxide (acts as magnet) (destroys H2O2)