Study smarter with Fiveable
Get study guides, practice questions, and cheatsheets for all your subjects. Join 500,000+ students with a 96% pass rate.
Every biological process you'll encounter on the AP Biology exam—from cellular respiration to DNA replication to immune responses—depends on understanding how molecules are built and why their structure determines their function. You're being tested on your ability to connect molecular structure, chemical properties, and biological roles across multiple units, from cell structure to genetics to evolution.
These four major macromolecules (plus water) aren't just a vocabulary list—they're the foundation for understanding how cells store energy, build structures, transmit information, and respond to their environment. Don't just memorize what each molecule does; know why its chemical properties make that function possible. When an FRQ asks about membrane structure or enzyme function, you need to trace the answer back to molecular principles.
Living organisms need both quick-access fuel and long-term reserves. The chemical bonds in carbohydrates and lipids store energy that cells release through metabolic reactions.
Compare: Carbohydrates vs. Lipids for energy storage—both store chemical energy in C-H bonds, but carbohydrates offer quick access while lipids provide more energy per gram for long-term reserves. If an FRQ asks about metabolic trade-offs, this distinction is key.
Genetic information must be stored accurately and transmitted reliably. Nucleic acids use a modular nucleotide structure that allows both stable storage and precise copying.
Compare: DNA vs. RNA—both are nucleic acids built from nucleotides, but DNA is double-stranded and stable (storage), while RNA is single-stranded and functional (expression). Know which nucleotides pair in each.
Proteins perform more diverse functions than any other macromolecule. Their three-dimensional shape—determined by amino acid sequence—dictates exactly what they can do.
Compare: Enzymes vs. Structural Proteins—both are proteins with specific shapes, but enzymes have active sites that bind substrates temporarily, while structural proteins maintain permanent physical arrangements. This distinction matters for questions about protein function.
Water isn't a macromolecule, but its unique properties make all biological chemistry possible. Polarity and hydrogen bonding explain nearly every property you need to know.
Compare: Hydrolysis vs. Dehydration Synthesis—both involve water and polymer bonds, but they run in opposite directions. Hydrolysis adds water to break bonds (digestion); dehydration synthesis removes water to form bonds (building macromolecules).
| Concept | Best Examples |
|---|---|
| Quick energy source | Glucose, monosaccharides |
| Long-term energy storage | Lipids (fats), glycogen, starch |
| Cell membrane structure | Phospholipids, cholesterol |
| Genetic information storage | DNA |
| Protein synthesis | mRNA, tRNA, rRNA |
| Enzymatic catalysis | Proteins with active sites |
| Structural support | Cellulose, collagen, chitin |
| Solvent and reaction medium | Water |
Which two macromolecules both store energy in C-H bonds, and what determines whether an organism uses one versus the other?
A protein loses its function when heated but retains its amino acid sequence. What structural level was disrupted, and why does this matter for enzyme activity?
Compare and contrast DNA and RNA in terms of structure, stability, and biological role.
How do water's polar properties enable both hydrolysis and dehydration synthesis reactions?
An FRQ asks you to explain how cell membrane structure relates to molecular properties. Which macromolecule would you focus on, and what specific chemical feature makes it suited for this role?