1. Organic Chemistry (or O-Chem)

Nomenclature: Diene refers to a compound that has two Alkenes in it. It also sounds like "dying", so, there you go.

2. Molecular Biology

mRNAs (messenger RNA) encode proteins ( let's be specific and say that processed, capped and tailed mRNAs contain only protein-coding regions). Non-coding RNAs, besides those regulatory ones, are considered "junk DNAs" therefore have nothing to do except for pairing within itself.

"Dog" here means something that's useless or of a lame quality.

3. Marine Biology

This I don't even have to say much about it. Who doesn't know the Angler Fish?

4. Molecular Bio

You get this one.