Pairing of Nucleic Acid Nucleotides
Cytosine and Guanine pair because C and G look similar.
Adenine and Thymine spell "AT," which could either refer to the word ("at") or those field things from Evangelion.
Of course, that's just for DNA. In RNA, Adenine pairs with Uracil. If you're rich, you can recall "AU" since that's the chemical symbol for gold. But we can't all be rich, so you can also remember that "AU" stands for "Alternate Universe." See "RNA has a U rather than a T" below for elaboration on the latter case.
Number of Bonds Between Paired Nucleotides
There are two bonds between A and T, and three bonds between C and G.
I remember the latter because my first two initials are C.G. (My first two names being Cornelius and Gartholemew), and I have three initials total if you count my surname.
If this doesn't apply to you, simply file for a name change. I hear they're easy and inexpensive in some places.
Purines vs Pyrimidines
The pyrimidines are Thymine and Cytosine (C and T), while all the rest (G, A, and U) are purines.
The letters of the pyrimidines spelled "TC," which stands for "Tower Control," the mode from Splatoon. In Tower Control mode, the objective is, as you'd expect, a tower, the top of which, get this, is shaped like a little pyramid.
RNA has a U rather than a T
Think of RNA as being DNA from the AU (Alternate Universe) where rather adenine pairing with thymine (so, AT), it pairs with uracil (AU).
The Lagging Strand in DNA Replication is made up of Okazaki Fragments
Easy to remember if you've played "CLANNAD" and didn't change the protagonist's name, or watched the anime I suppose. You recall how late Okazaki always was? Could say he was lagging behind.
As a bonus, it's a rather shoddy and stupid nomonomic, but you could maybe remember that the gaps between Okazaki fragments are sealed by an enzyme called DNA Ligase since "Ligase" sounds a bit like "Ligma," the juvenile disease. Okazaki's good "friend" Sunohara could most definitely be convinced of the existence of this affliction.
Pinocytosis is "Cell Drinking"
Piña Colada is a drink. Pino -> Piña.
Stomata vs Stroma
Stomata (singular: stoma) are these little microscopic pores on leaves, while stroma is the fluid within chloroplasts. Their names are similar, which is troublesome.
I remember that stroma is the fluid since it has an r in it, which I imagine as standing for "runny."
The Kreb Cycle Occurs in the Mitochondrial Matrix
I made a game titled Fkreb whose name was quite frankly random keyboard mashing, but it happened to resemble "Kreb" (just with an F at the start). Being a video game, of course, its events occur in a digital world.
Meanwhile, the film "The Matrix" posits the idea that our whole world could simply be a simulaton. In other terms, a digital world.
So, in the same way Fkreb takes place in a "Matrix," a digital world, the Kreb Cycle takes place in the Mitochondrial Matrix.
Catabolic Processes Break Molecules Down
Cats are known to break stuff. You've read a comic strip before, right?
Bonus Mnenomic: How to Spell "Gullible"
This one's helpful to have, since gullible isn't actually in the dictionary, nor is it in the thesauraus.
Whenever you're having trouble spelling this word, simply look to the ceiling. It is written there.
Disclaimer
Every time you use one of my original memnomics, you've got to mail me 500 dollars cash in unmarked bills. Don't forget!