ECA Study Guide — Exam Prep

Carbon: The Skeleton of Life

Carbon forms the skeleton of all organic macromolecules because it can form four bonds. This allows carbon to build long, continuous chains (and rings) with diverse shapes.

In skeletal (line) drawings, every corner and end of a line is a carbon atom
Counting carbons: a zigzag with 6 vertices/ends = 6 C; a 5-sided ring = 5 C; a branched "Y" shape with 4 ends/vertices = 4 C
Functional groups attached to the carbon skeleton add O, N, P (and S) atoms

Four Macromolecule Classes & Their Monomers

Large biological molecules are built from smaller repeating units called monomers.

Carbohydrates → monomer: monosaccharide (e.g., glucose)
Proteins → monomer: amino acid
Nucleic acids → monomer: nucleotide
Lipids are not true polymers, but include fats (triglycerides), phospholipids, and steroids

Dehydration Synthesis & Hydrolysis

Dehydration synthesis (a condensation reaction) links two monomers together. Water is a PRODUCT because a water molecule is removed to form the new bond.

Hydrolysis breaks apart a macromolecule by adding water. Water is a REACTANT because it is used up to break the bond.

Dehydration synthesis: builds up; releases H₂O
Hydrolysis ("water-splitting"): breaks down; uses H₂O

Functional Groups

Functional groups are clusters of atoms attached to the carbon skeleton that give a molecule its chemical properties. All four below are polar.

Hydroxyl / alcohol (–OH): polar; found in carbohydrates, some amino acids, and nucleic acids
Amino / amine (–NH₂): polar and basic; found in ALL amino acids and in the nitrogenous bases of nucleic acids
Carboxyl / carboxylic acid (–COOH): polar and acidic; found in ALL amino acids
Phosphate (–PO₄²⁻): polar; found in phospholipids and nucleic acids

Which Elements Are in Which Molecules?

Every biological molecule has C, H, and O. Nitrogen, phosphorus, and sulfur appear only in certain classes.

Carbohydrates (and glucose): C, H, O
Lipids (triglycerides) and steroids: C, H, O
Phospholipids: C, H, O, P
Proteins and enzymes: C, H, O, N, and S (sulfur in some amino acids)
Nucleic acids and DNA: C, H, O, N, P

Identifying Structures

Know how to recognize each class of macromolecule from a drawing.