BACTERIAL CELL WALL FUNCTIONS OF CELL WALL PROTECTS

BACTERIAL CELL WALL

FUNCTIONS OF CELL WALL PROTECTS CELL WALL COMPONENTS- ANTIGENICITY PROTECTS SITE FROM OSMOTIC LYSIS FROM TOXIC SUBSTANCES OF ACTION OF SEVERAL ANTIBIOTICS GRAM STAINING DIFFERENTIATES GRAM POSITIVE AND GRAM NEGATIVE

GRAM POSITIVE 20 - 80 nm thick PEPTIDOGLYCAN/ MUREIN

GRAM NEGATIVE 2 - 7 nm thick PEPTIDOGLYCAN 7 -8 nm thick OUTER MEMBRANE

PERIPLASMIC SPACE

PERIPLASMIC SPACE Space between outer membrane and plasma membrane Larger in Gram Negative 30 - 70 nm wide

PERIPLASMIC SPACE In Gram-positive bacteria a smaller periplasmic space is found between the inner membrane and the peptidoglycan layer

PEPTIDOGLYCAN STRUCTURE 2 ALTERNATING SUGAR DERIVATIVES N-Acetyl Glucosamine N-Acetyl Muramic acid (lactyl ether of N- Acetyl glucosamine): Carboxy group with tetrapeptide chain-D & L amino acids Amino acids- few are not found in proteins: protects against degradation by peptidases

PEPTIDOGLYCAN STRUCTURE

Diamino acids (3 rd position) Meso-Diaminopimelic acid/ L-lysine

INTERBRIDGES

PEPTIDOGLYCAN SAC LIKE STRUCTURE STRONG ENOUGH TO RETAIN THEIR SHAPE AND INTEGRITY YET THEY ARE ELASTIC AND SOMEWHAT STRETCHABLE POROUS-MOLECULES CAN PENETRATE

PEPTIDOGLYCAN STRUCTURE

GRAM POSITIVE CELL WALL TEICHOIC ACIDS Polymers of glycerol or ribitol joined by Phosphate groups R- Alanine/ glucose Teichoic acids- Connected to PG or Lipids in plasma membrane (Lipoteichoic acids) Negatively charged

TEICHOIC ACIDS/ LIPOTEICHOIC ACIDS

FUNCTION OF TEICHOIC ACIDS Maintaining the structure of the cell wall Imparts negative charge to the cell wall Not present in Gram negative cells

GRAM NEGATIVE 2 - 7 nm thick PEPTIDOGLYCAN 7 -8 nm thick OUTER MEMBRANE

Outer membrane (LPS) Lipid A Core Polysaccharide O Antigen No teichoic acids

LIPOPOLYSACCHARIDE LAYER

LPS LAYER Unusual sugars Abequose Heptulose Keto- deoxy Octonate O- ANTIGEN Rapidly changes Avoids detection by host antibodies

LPS LAYER- Attachment Brauns Lipoprotein (Underlying Peptidoglycan) Direct Contact regions (20 - 100 nm areas)

LPS LAYER- FUNCTIONS Avoidance of host defenses Core polysaccharides- sugars and phosphatecontributes to negative charge Helps stabilize membrane structure Lipid A- toxic- Endotoxin Protective barrier- slows the entry of bile salts, antibiotics and other toxic substances

LPS LAYER- FUNCTIONS…. More permeable than plasma membrane 3 porin proteins cluster- forms channel through which molecules smaller than 600700 daltons can pass Larger molecules- Vit B 12 must be transported by carriers Prevents loss of periplasmic enzymes

SUMMARY GRAM POSITIVE CELL WALL Peptidoglycan Teichoic acids/ Lipoteichoic acids GRAM NEGATIVE CELL WALL Peptidoglycan Lipopolysaccharide Layer

TRUTHFULNESS SPEAKING ONLY THAT IS HONEST AND FACTUAL

TRUTHFULNESS TRUTHFUL LIPS ENDURE FOR EVER BUT A LYING TONGUE IS BUT FOR A MOMENT

TRUTHFULNESS A man is never more truthful than when he acknowledges himself a liar. Mark Twain