AP Biology Unit 1 Notes: Understanding Biological Macromolecules

Biological macromolecules

Large, carbon-based molecules used by organisms to store energy, build cellular structures, transmit information, and carry out chemical reactions (carbohydrates, lipids, proteins, nucleic acids).

Structure determines function

Principle that a macromolecule’s specific arrangement of atoms (its structure) determines its chemical behavior and biological role.

Carbon backbone (of life)

Carbon’s ability to form four covalent bonds allows long chains, branches, and rings, creating diverse biological molecules with different shapes and properties.

Monomer

A small molecular subunit that can be linked to other subunits (e.g., an amino acid).

Polymer

A large molecule made of many repeating monomer units linked together (e.g., a polypeptide).

Dehydration synthesis (condensation reaction)

Builds polymers by forming a covalent bond between monomers while removing a molecule of water.

Hydrolysis

Breaks polymers into monomers by adding water to help break a covalent bond.

Functional group

A specific cluster of atoms that behaves in consistent ways and helps determine a molecule’s properties (polarity, acidity/basicity, reactivity).

Hydroxyl group (-OH)

Functional group that often increases polarity and water solubility; common in sugars.

Carboxyl group (-COOH)

Functional group that can donate H+ (acidic); found in amino acids and fatty acids.

Amino group (-NH2)

Functional group that can accept H+ (basic); found in amino acids.

Phosphate group (-PO4)

Functional group that often contributes negative charge and is important in energy transfer and nucleic acids.

Hydrophilic

Describes polar or charged regions that interact well with water.

Hydrophobic

Describes nonpolar regions that do not interact well with water and tend to cluster away from it.

Amphipathic

Having both hydrophilic and hydrophobic regions (e.g., phospholipids with a polar head and nonpolar tails).

Isomer

A molecule with the same molecular formula as another molecule but a different structure, often leading to different biological function.

Covalent bond

A strong bond that holds the main backbone of polymers together (e.g., glycosidic, peptide, phosphodiester bonds).

Hydrogen bond

A weak interaction important for macromolecule shape, such as DNA base pairing and protein secondary structure (strong collectively, weak individually).

Glycosidic linkage

The covalent bond that links monosaccharides together in carbohydrates; formed by dehydration synthesis.

Triglyceride

A lipid made from glycerol and fatty acids; used for long-term energy storage and insulation due to many C-H bonds and low water attraction.

Saturated fatty acid

A fatty acid with no double bonds; straighter chains that pack tightly (often associated with more solid fats).

Unsaturated fatty acid

A fatty acid with one or more double bonds; kinked chains that pack less tightly, increasing membrane fluidity when present in phospholipids.

Peptide bond

The covalent bond linking amino acids in a polypeptide; formed by dehydration synthesis.

Nucleotide

The monomer of nucleic acids, consisting of a phosphate group, a five-carbon sugar (ribose or deoxyribose), and a nitrogenous base.

Phosphodiester bond

The covalent bond that links nucleotides, connecting the sugar of one nucleotide to the phosphate of the next to form the sugar-phosphate backbone.