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'''Bacterial Cell Wall Structure'''

The bacterial cell wall is crucial for maintaining the structural integrity of bacteria and protects bacteria from osmotic stress and toxic compound. The cell wall is composed of peptidoglycan (Figure 2), and in Gram positive bacterial species (e.g. S. aureus) is many layers thick, while in Gram negative bacterial species (e.g. Escherichia coli) is only a few layers thick. The difference in the number of peptidoglycan layers accounts for the differential staining of these two groups of organisms. Peptidoglycan consists of a carbohydrate portion: alternating residues of [http://en.wikipedia.org/wiki/N-Acetylmuramic_acid N-acetylmuramic Acid (NAM)] and [http://en.wikipedia.org/wiki/N-Acetylglucosamine N-acetylglucosamine (NAG)] that polymerize to form long chains, and a protein portion: a pentapeptide chain that terminates with to D-alanines (D-Ala) residues. The pentapeptide chains are covalently bound to each NAM residue. Rows of peptidoglycan are cross-linked together with pentaglycine chains to form a "mesh-like" structure. This cross-linking reaction is catalyzed by TPs.

'''Catalytic Mechanism of Action of Transpeptidases'''

[[Image:Schematic TP 3steps.jpg|thumb|alt= Alt text|Figure 2. Schematic showing Catalytic Mechanism of PBP2a |550px]]

(a)The D-Ala side-chain substrate accesses the TP active site.

(b)The active site serine residue nucleophilically attacks the peptide bond between the terminal D-Ala residues. Terminal D-Ala residue exits the active site, and the remaining D-Ala residue forms a covalent bond with the active site serine residue to form an acyl-TP complex.

(c)Subsequently, a pentaglycine chain enters the TP active site through nucleophillic attack forms a covalent bond with the D-Ala formerly bound to the active site serine residue. As a result, the TP site serine residue is regenerated. The entire process takes approximately 4 seconds.

'''Mechanism of Action of B-Lactam antibiotics'''

The B-Lactam antibiotics inhibit bacterial cell growth by irreversibly inhibiting TP's and, therefore, bacterial cell wall sythesis. Specifically, B-Lactams are molecular mimics of a portion of the peptidoglycan polymer, namely the D-Ala-D-Ala moiety, which is the normal TP enzymatic substrate(Figure 4)

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@@ Line 5: / Line 5: @@
 '''Bacterial Cell Wall Structure'''
 The bacterial cell wall is crucial for maintaining the structural integrity of bacteria and protects bacteria from osmotic stress and toxic compound. The cell wall is composed of peptidoglycan (Figure 2), and in Gram positive bacterial species (e.g. S. aureus) is many layers thick, while in Gram negative bacterial species (e.g. Escherichia coli) is only a few layers thick. The difference in the number of peptidoglycan layers accounts for the differential staining of these two groups of organisms. Peptidoglycan consists of a carbohydrate portion: alternating residues of [http://en.wikipedia.org/wiki/N-Acetylmuramic_acid N-acetylmuramic Acid (NAM)] and [http://en.wikipedia.org/wiki/N-Acetylglucosamine N-acetylglucosamine (NAG)] that polymerize to form long chains, and a protein portion: a pentapeptide chain that terminates with to D-alanines (D-Ala) residues. The pentapeptide chains are covalently bound to each NAM residue. Rows of peptidoglycan are cross-linked together with pentaglycine chains to form a "mesh-like" structure. This cross-linking reaction is catalyzed by TPs.
+'''Catalytic Mechanism of Action of Transpeptidases'''
+[[Image:Schematic TP 3steps.jpg|thumb|alt= Alt text|Figure 2. Schematic showing Catalytic Mechanism of PBP2a |550px]]
+(a)The D-Ala side-chain substrate accesses the TP active site.
+(b)The active site serine residue nucleophilically attacks the peptide bond between the terminal D-Ala residues. Terminal D-Ala residue exits the active site, and the remaining D-Ala residue forms a covalent bond with the active site serine residue to form an acyl-TP complex.
+(c)Subsequently, a pentaglycine chain enters the TP active site through nucleophillic attack forms a covalent bond with the D-Ala formerly bound to the active site serine residue. As a result, the TP site serine residue is regenerated. The entire process takes approximately 4 seconds.
+'''Mechanism of Action of B-Lactam antibiotics'''
+The B-Lactam antibiotics inhibit bacterial cell growth by irreversibly inhibiting TP's and, therefore, bacterial cell wall sythesis. Specifically, B-Lactams are molecular mimics of a portion of the peptidoglycan polymer, namely the D-Ala-D-Ala moiety, which is the normal TP enzymatic substrate(Figure 4)