Antibiotics Flashcards

Class: β-Lactam antibiotics Examples: Penicillins (e.g. Penicillin V, amoxicillin), cephalosporins (e.g. cephalexin (oral)) Why they work: 

β-Lactams prevent the crosslinks from joining the tetra-peptide side chains

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Inhibiting cell wall synthesis usually leads to the death of the cell

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Osmotic pressure is high in the cell so any damage to the rigid cell wall usually leads to the structural breakdown of the cytoplasmic membrane

Class:  Bacterial Folate Antagonists Examples: Sulphonamides (e.g. sulphanilamide), trimethoprim Why they work: 

We get folic acid through diet but bacteria make their own supply

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This folate pathway is very important in cell metabolism

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This is the ‘selective toxicity’ target

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They are competitive inhibitors, binding to intermediat intermediate e molecules in the folate pathway, preventing it from progressing further Sulphonamides and trimethoprim block different processes and so can be used together from increased efficacy (a sequential blockage) blockage)

Class: Aminoglycosides Examples: streptomyci streptomycin, n, gentamycin Why they work: 

Form ionic bonds to the cell surface

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Penetrate the membrane and diffuse into the cytoplasm

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Bind to the ribosomes

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Distorts the shape of the ribosome by binding between the 30s and 50s subunits, causing the misreading of the mRNA

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The wrong tRNA comes in, resulting in a non-functional protein being synthesised

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Must be injected, are kept for bad injections

Class: Tetracyclines Examples: tetracycline Why they work: 

Prevent the attachment of the tRNA to the ribosome-mRNA complex

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Prevents the addition of amino-acids to the peptide chain

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They bind to calcium, and so aren’t used in children as they can build up in the

bones and teeth, causing a fault line

Example: Chloramphenicol Why they work: 

Binds to the bacterial ribosome (blocking peptidyl transferase)

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This prevents amino-acids from being added

Example: Erythromycin Why they work: 

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Stops the peptide bond from forming and prevents the translocation of the ribosome along the mRNA Often used for people who are allergic to penicillins

Example: Clindamycin Why they work: 

Similar mechanism of action to erythromycin, binding to the 50s subunit and preventing the ribosomal translocation

Class: Fluoroquinolones Examples: cirproflaxin (broad-spectrum), cinoxacin (narrower-spectrum) Why they work:  

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Inhibit bacterial DNA gyrase enzyme This enzyme catalyses the introduction of the negative supercoil into the DNA, allowing transcription and translation Synthetic antibiotics recently introduced into clinical practice, the first products of rational drug design