Cephalosporins are a class of β-lactam antibiotics that work by inhibiting the enzyme transpeptidase, which is crucial for bacterial cell wall synthesis. The mechanism of action involves the following steps:
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Structural Similarity: Cephalosporins have a β-lactam ring that is structurally similar to the D-Ala-D-Ala moiety of the peptidoglycan layer, which is the target of transpeptidases (also known as penicillin-binding proteins or PBPs).
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Covalent Binding: When cephalosporins bind to the active site of the transpeptidase enzyme, they form a stable covalent bond. This effectively inhibits the enzyme's activity because it prevents the cross-linking of peptidoglycan chains necessary for bacterial cell wall integrity.
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Inhibition of Cell Wall Synthesis: By inhibiting transpeptidases, cephalosporins block the synthesis of peptidoglycan. Without a properly formed cell wall, bacteria cannot maintain their structure, leading to lysis and ultimately, cell death.
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Resistance Mechanisms: Some bacteria produce β-lactamases, enzymes that can hydrolyze the β-lactam ring of cephalosporins, rendering them ineffective. Structural modifications in newer cephalosporins are designed to overcome this resistance.
In summary, cephalosporins irresponsibly inhibit transpeptidase by mimicking the substrate of the enzyme, causing a covalent modification that shuts down its function, impairing bacterial cell wall synthesis, and leading to bacterial cell death.
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