"Why does this molecule look the way it does?" In Caltech chemistry professor Brian Stoltz's class for CRI's 2025 Winter Online Research Program, that question came before any formula. Stoltz would put up a drawing of a single molecule and start asking questions about it. The molecule at the heart of the course was one almost everyone has heard of: penicillin.
Many families picture organic chemistry as a hard subject built on formulas and memorization. Stoltz's class ran differently. Instead of drilling problem sets, it followed the story of one real medicine: how it is made, and why it works. Students did not stop at learning concepts. They went deep on a single topic and wrote it up as a research paper.
Starting from shape
Rather than filling the board with complex calculations, Stoltz built his explanations around a molecule's shape and its distinctive features. From that first question about shape, he kept pushing further:
- Doesn't this part look unstable?
- Why does this structure break apart so easily?
- What reactions could this shape lead to, and what happens then?
Penicillin gave those questions a concrete answer. The molecule, Stoltz explained, contains a structure that breaks apart especially easily. (Chemists know that fragile part as the four-membered beta-lactam ring.) That fragility is what lets penicillin attack bacteria. It is also what makes the drug so tricky to make. Once students saw that trade-off, penicillin stopped being just the name of a medicine and became something they could explain.
Five students, one paper
If Stoltz's sessions sketched the big picture, the TA-led sessions were where students worked as researchers. Rather than all five skimming the same material, they divided one paper into parts:
- Student A: how penicillin was first discovered, and the trial and error it took to work out its structure
- Student B: how fungi in nature produce penicillin
- Student C: the methods developed to manufacture the drug at industrial scale
- Student D: how penicillin attacks bacteria, and why it is relatively safe for people
