AP Biology Unit 1: Chemistry of Life
Water, macromolecules and their structure-function relationships.
Unit overview
Living systems are built from a few elements arranged into four kinds of macromolecule. Water's polarity and hydrogen bonding give it cohesion, adhesion, high specific heat and the ability to dissolve many substances, which is why cells are mostly water.
Carbohydrates, lipids, proteins and nucleic acids are assembled from monomers by dehydration synthesis and broken down by hydrolysis. Structure determines function: a protein's amino acid sequence determines how it folds through primary, secondary, tertiary and quaternary structure, and a change in one amino acid can change the shape and activity of the whole molecule. Nucleic acids store information in the sequence of nucleotides and have directionality, running to .
Key topics
- Properties of water
- Hydrogen bonding explains cohesion, surface tension, high specific heat and solvent behaviour.
- Macromolecules
- Monomers, polymers and the bonds that link them.
- Protein structure
- Four levels of structure and how R-group interactions shape folding.
- Nucleic acids
- DNA and RNA nucleotides, base pairing and antiparallel strands.
Common mistakes
- Confusing dehydration synthesis (builds polymers, releases water) with hydrolysis (breaks them, uses water).
- Saying hydrogen bonds hold the atoms of a water molecule together; those are covalent bonds, while hydrogen bonds link separate molecules.
- Describing protein structure without connecting it to function.
Exam tips
- Free-response answers score well when they link a structural feature to a specific function.
- Know which elements each macromolecule contains, such as nitrogen in proteins and nucleic acids and phosphorus in nucleic acids and phospholipids.
More practice on this site
See the AP Biology exam format and every unit on the course page.