Podcast
Questions and Answers
Which antibiotic specifically inhibits the MurA enzyme in the PDG biosynthesis pathway?
Which antibiotic specifically inhibits the MurA enzyme in the PDG biosynthesis pathway?
What is the role of transpeptidase (PBP) during the biosynthesis of PDG?
What is the role of transpeptidase (PBP) during the biosynthesis of PDG?
Which type of teichoic acid is associated exclusively with Gram-positive bacteria?
Which type of teichoic acid is associated exclusively with Gram-positive bacteria?
Bacitracin inhibits which specific process in PDG biosynthesis?
Bacitracin inhibits which specific process in PDG biosynthesis?
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The conversion of L-alanine to D-alanine is catalyzed by which enzyme?
The conversion of L-alanine to D-alanine is catalyzed by which enzyme?
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What structural feature is highlighted by the β-(1,4)-glycosidic bond in the disaccharide unit of wall teichoic acids?
What structural feature is highlighted by the β-(1,4)-glycosidic bond in the disaccharide unit of wall teichoic acids?
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How does D-cycloserine affect the synthesis of PDG?
How does D-cycloserine affect the synthesis of PDG?
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What is the primary function of autolysins in the context of PDG?
What is the primary function of autolysins in the context of PDG?
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Which antibiotic binds to the D-Ala-D-Ala segment and inhibits transpeptidation?
Which antibiotic binds to the D-Ala-D-Ala segment and inhibits transpeptidation?
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Study Notes
Peptidoglycan (PDG) Biosynthesis
- Peptidoglycan synthesis occurs in the cytosol
- NAG/NAM-pentapeptide synthesis takes place in the cytosol
- Phosphoenolpyruvate (PEP) forms NAM via transferase enzyme
- Fosfomycin is a MurA enzyme inhibitor (UDP-N-acetylglucosamine-enolpyruvyltransferase)
- L-alanine is converted to D-alanine via Alanine racemase; a 2 step process, creating D-alanyl-D-alanine
- D-cycloserine inhibits both enzymes (alanine racemase and D-Ala-D-Ala synthetase)
- Bactoprenol transports NAG/NAM-P
- Bacitracin inhibits this transport
PDG Biosynthesis and Antibiotics
- Autolysins break β-(1-4) glycosidic bonds of PDG
- NAG/NAM-P is inserted into old PDG
- Transglycosidase step catalyzes formation of the glycosidic bonds; the second step of PDG biosynthesis
- Vancomycin inhibits Transglycosidase
- Transpeptidase (PBP) reforms peptide cross-links, final step in PDG biosynthesis
- β-lactams inhibit Transpeptidase
- Vancomycin binds to D-Ala-D-Ala and prevents binding to PBP
- Prevent cross linking
Teichoic Acids (TA)
- Associated with Gram-positive bacteria only
- 50% of the Gram-positive cell wall weight
- Cell surface anionic glycopolymers
- Responsible for negative charge
- Highly immunogenic
- Mediate adherence to mucosal cells
Types of Teichoic Acids
- Two types of TAs
- WTAs divided into 2 components
- Disaccharide unit
- N-acetylmannosamine & NAG-1-phosphate, connected by β-(1,4)-glycosidic bond
- NAG of disaccharide unit is covalently linked to 6-OH of NAM in PDG
- Disaccharide unit
- LTA (Lipoteichoic acid) Main chain polymer
- 40-60 units of glycerol or ribitol joined via phosphodiester bonds
- LTA is linked to cytoplasmic membrane with a glycolipid anchor
- Glycolipid anchor is a disaccharide unit of glucose, linked by β-(1,6)-glycosidic bond to a diacylglycerol
- Function of WTA: Cell shape determination, cell division regulation, pathogenesis, antibiotic resistance
- Function of LTA: Protection against cationic antimicrobial peptides
Cell Wall Functions
- Determines and maintains cell shape
- Counters osmotic pressure, prevents cell lysis
- Provides attachment sites for bacteriophages
- Provides a rigid platform for surface appendages (flagella, fimbriae, pili)
- Essential role in cell division
- Site of major antigenic determinants of the cell surface
- Resistance to antibiotics
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Description
This quiz explores the intricate process of peptidoglycan biosynthesis, with a focus on the enzymatic actions and roles of various antibiotics. Learn how inhibitors like fosfomycin, vancomycin, and bacitracin affect this vital bacterial process. Test your knowledge on how NAG and NAM are synthesized and incorporated into the bacterial cell wall.
