A key skill for the exam is matching a function or description to the correct macromolecule class.
Carbohydrate: short-term energy; makes up plant cell walls
Lipid: long-term energy storage (fats); makes up the cell membrane (phospholipids); steroids; phospholipids have both hydrophobic and hydrophilic properties
Protein: some proteins have both hydrophobic and hydrophilic regions; enzymes
Nucleic acid: contains the genetic code
Quick Reference: Elements
Use this to answer "which elements does this molecule contain?"
Carbohydrates, glucose, triglycerides, steroids: C, H, O
Phospholipids: C, H, O, P
Proteins, enzymes: C, H, O, N, S
Nucleic acids, DNA: C, H, O, N, P
Identify the Molecule
Practice classification from drawings:
Four fused rings with an OH → steroid (lipid)
Glycerol with three long tails → fat (lipid)
Central C with NH₃⁺, COO⁻, H and a side chain → amino acid (protein)
Two sugar rings joined → carbohydrate
Sugar + base + three phosphates (ATP) → nucleotide (nucleic acid)
Two amino acids joined by a peptide bond → amino acid (dipeptide) / protein