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Lecture 5

BIO 3124 Lecture Notes - Lecture 5: Galactose, Cell Membrane, Peptidoglycan


Department
Biology
Course Code
BIO 3124
Professor
Angela Yeung
Lecture
5

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LECTURE 5: CELL WALLS & EXTERNAL STRUCTURES
BACTERIAL CELL WALLS
Provide structure and shape and protect cell from osmotic forces
Assist some cells in attaching to other cells or in resisting antimicrobial drugs
Can target cell wall of bacteria with antibiotics
Give bacterial cells characteristic shapes
Composed of peptidoglycan
Scientists describe two basic types of bacterial cell walls
Gram-positive and Gram-negative
PEPTIDOGLYCAN
Polymer of 2 repeating sugar derivatives
N-acetylglucosamine & N-acteylmuramic acid
Linked by b-1,4 glyosidic bond
Peptide linkage of muramic acid residues confer added strength
L-alanine, D-glutamic acid, D-alanine
L-lysine in Gram +ve,
diaminopimelic acid (DAP) in Gram -ve
Gram +ve cross link can occur through a short interbridge of amino acids
Gram –ve peptide bond forms between the amino group of DAP and to the glycan chain of the
carboxyl in D-alanine on the adjacent chain
Lysosomez in tears/saliva breaks b-1,4 glycosidic bonds and in essence can kill bacteria
GRAM-POSITIVE CELL WALL
Multiple layers of peptidoglycan (90%)
L-lysine
Crosslink via peptide bridge
Contains teichoic acid
Acidic polysaccharides composed of repeating glycerol phosphate or ribitol phosphate
units
Lipoteichoic acids
Associated with lipids of cytoplasmic membrane
Helps attract cationic ions, tension surfaces, recognize specific host cells, shape,
mutanogenesis
TECHOIC ACIDS
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Embedded cell wall, cytoplasmic membrane and capsular polymers
Acidic polysaccharides composed of repeating glycerol phosphate or ribitol phosphate units
GRAM-NEGATIVE CELL WALL
Single layer of peptidoglycan (10%)
Diaminopimelic acid (DAP)
Direct crosslink between tetrapeptides
No teichoic acid
More complex;
Has a outer membrane covering a thin layer of peptidoglycan (i.e., in periplasmic space between
outer and cytoplasmic membranes);
Outer membrane anchored to peptidoglycan by a lipoprotein;
Another structure found only in outer membrane is lipopolysaccharide (LPS);
Outer membrane is a selective barrier based on size and charge of molecules
In gram strain, alcohol increases permeability of Gram-negative outer membrane but shrinks pores
of Gram-positive peptidoglycan
THE CELL WALL OF BACTERIA
Prokaryotes That Lack Cell Walls
Mycoplasmas
Group of pathogenic bacteria
Mycoplasma usually intracellular pathogenic bacteria, therefore host can
maintain internal osmotic pressures – can also scavenge sterols from host to
enforce cytoplasmic membrane
Thermoplasma
Species of Archaea
THE CELL WALL OF ACHAEA
No peptidoglycan
Typically no outer membrane
Pseudomurein
Polysaccharide similar to peptidoglycan
Composed of N-acetylglucosamine and N-acetyltalosaminuronic acid
Found in cell walls of certain methanogenic Archaea
Cell walls of some Archaea lack pseudomurein
More diverse
Some methanogens contain pseudo peptidoglycan (pseudomurein)
NAG & N-acetylalosaminuronic acid
Linked by b-1,3 glycosidic bond - Linkages are different (b-1,3 glycosidic bond) – insensitive to
lysosomes bc its only sensitive to b-1,4
Some lack pseudomurein but contain other polysaccharides – such as glucose, glucoronic acid etc.
depending on environments
Methanosacrcina have thick walls composed of glucose, glucuronic acid, galactosamine
uronic acid and acetate
Extreme halophile Halococcus contain sulfate which binds the Na ions from the
environment
Most common is S-layer
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