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Cell Wall of Acid Fast Bacteria
@Contains an inner peptidoglycan layer and an
outer membrane layer .
@ The inner peptidoglycan layer is joined to the cell membrane by the Phosphatidyinositol mannosides (PIM) chain
@Also the inner peptidoglycan layer is joined
to an arabinogalactan layer (arabinose and
galactose) by a lipoarabinomannan chain .
@The arabinogalactan layer is attached directly to the mycolic acids layer .
@The mycolic acids layer is followed by a layer of acyl lipids.
@Porins are found to transport the hydrophilic
molecules through the outer membrane layer .
@Proteins are located on the surface of cell
@Mycolic acids are esterified to form polysaccharides (wax D) and glycolipids.
@Lipids are responsible for: * Acid fast staining
* Stickiness of mycobacteria
Bacterial L-Forms
@Loss of cell wall because murein for wall
synthesis is absent
@Spheroplasts: gram negative L-forms
@Protoplasts: gram positive L-forms
@Origin : * Spontaneous (Streptobacillus,
Bacteroides) *Presence of penicillin or lysozyme * Destruction of wall by complement
* Absence of nutrient for wall synthesis
@No pathological or clinical significance.
Bacterial Cell MembraneStructure:
@ Composed of 3 layers:
@ 2 phospholipids layers with phosphate heads and lipid tails.
@ They are hydrophilic at their phosphate heads and hydrophobic at their lipid tails.
@ The hydrophobic lipid tails point inwards and the hydrophilic phosphate heads point outwards. @ Glycoproteins point outwards & attached to carbohydrate chain
@ Integral proteins help to anchor the cytoskeleton in place.
@ Transmembrane proteins have enzymatic activity & catalyze chemical reactions
@ The third layer is the hydrophobic region.
@ It contains proteins (70%) and lipids (30%)
@ ٍCM: semipermeable to nutrients, water, salts
@ Folded towards cytoplasm to form mesosome
Functions of Cell Membrane
@ Forms an osmotic barrier between cytoplasm and environment
@ Transport of: # Respiratory electrons # Nutrients inside cell.
# Waste product outside cell
@ Synthesis and transfer of peptidoglycan, teichoic acids, & other contents of cell wall
@ Secretion of extracellular enzymes and toxins
@ Segregation of chromosomal and plasmid DNA
into daughter cells.
Mesosomes
@ Mainly invaginations of cell membrane@ Functions include: # Involved in nuclear division # Provide respiratory enzymes # Excretion of material outside the cell # Involved in cell wall synthesis # Involved in cell wall division
@ Convoluted & formed of lamellae or vesicles.
@ Developed in mycobacteria, E. coli, Bacillus
@ May join cell wall or nuclear body
Cytoplasm
@ Contains: water, ions, metabolites, proteins, nucleic acids, storage granules, ribosomes.
@ Ribosomes actively translating messenger RNA into proteins.
@ Storage granules serve as reserves of energy
and nutrients.
@ Metachromatic (volutin) granules are reserves
of high energy phosphates in corynebacteria.
@ Contains the bacterial chromosome as a single circular molecule.
Bacterial Nucleoid
@Bacterial chromosomal DNA is not enclosed
by an envelope
@The chromosomal DNA molecule is 1.6 mm in
a form of coil .
@ Plasmid is a separate DNA molecule that can replicate independently
@ Plasmids are double-stranded and circular. Their number can range from 1 to thousands.
@ Plasmids can integrate and replicate with bacterial cells.
Endospores
@ Induced by: Changes of pH, temp., oxygen tension, nutrients, waste products, moisture, minerals (Ca++, Mn, K).
@ Differences from vegetative cells: # More resistant to heat, disinfectants, dryness, starvation # Low water content (5 - 20%) # Thick, impermeable coat # Low metabolic activity # Contain Ca++ and dipicolinic acid
Endospore Structure
@Endospores form within a vegetative bacterial cell
@Exosporium: a thin delicate covering
@ Spore coat: thick layer of protein & keratin
@ Cortex: made of peptidoglycan
@ Core wall
@ Core: contains ribosomes and nucleoid
Cycle of spore formation and germination:
@ Bacterium makes a copy of its chromosome DNA & the bacterial cell membrane begins invaginating inward until there’s a little daughter cell within the mother cell.
@ Next, membrane of mother cell surrounds the daughter cell. Then two membrane layers will surround the daughter cell.
@ Then a thick peptidoglycan wall forms and a tough outer protein coat forms around all daughter cell, which is now spore.