Thought of the day

It amazes me how the first run of (almost) spring is both the best and worst run of my life. Every year.

How penicillin works

I’m currently in the midst of a short break I’m taking whilst studying for a massive microbio test I have in a few hours. And what better way to take a break than to post about one of the essay questions I know will be on the exam?

β-lactam antibiotics include penicillin and cephalosporins. (Everything that follows applies to both, but most people seem to be more interested if the topic is the more familiar penicillin subgroup.) The way these antibiotic works is by attacking the cell walls of bacteria. This makes gram-positive bacteria more susceptible than gram-negative bacteria; gram-positive bacteria have an outer peptidoglycan layer whereas gram-negative bacteria have their peptidoglycan layer between a plasma-membrane layer and an LPS layer. (No, I’m not going to define all these terms I’m using.)

Transpeptidase molecules are necessary for catalyzing cross-linking of glycan-linked peptide chains. Penicillin, all coy and sneaky, causes transpeptidase to link to it (penicillin) instead. (Transpeptidases are known as penicillin-binding proteins, or PBPs. I find the name misleading since it sounds like their purpose is to get all buddy-buddy with penicillin.) This prevents cross-linking. As I’m sure every nerd knows, cross-linking is what gives the peptidoglycan outer wall much of its strength. So while cell wall synthesis continues unabated, no cross-linking is happening, thus weakening structural integrity. Mike Holmes would be pissed if he was a biologist and he saw this happening. (Come on, HGTV fans, I know you’re out there.) Furthermore, autolysins are being released. What this means is the gram-positive bacteria has a weak and self-degrading outer wall. Osmotic pressure eventually causes lysis.

Now please excuse me while I enter hour 6 of studying for the (literally) 109 other things I need to know for my upcoming test.

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