Three Parts, One Rung, Every Instruction

A nucleotide is three pieces of chemistry — a phosphate, a five-carbon sugar, a nitrogenous base — and the molecule that stores every instruction for building you is nothing more than those three, linked over and over in one direction. The backbone is covalent and runs 5′→3′. The rungs are hydrogen bonds, the same weak attraction that bent water into a solvent back in 1.1, now holding heredity together loosely enough to be read. Two bonds, two strengths, two jobs. Confuse them and the whole molecule stops making sense.

AP BIOLOGY · 8 STEPS · 6 QUICK CHECKS · PHOSPHATE + SUGAR + BASE · BACKBONE = COVALENT · RUNGS = HYDROGEN BONDS · ANTIPARALLEL 5′→3′ · v1