Overview
This lecture reviews the four main types of biological macromolecules, emphasizing how structure determines function, with detailed focus on carbohydrates, proteins, nucleic acids, and lipids.
Macromolecules Overview
- The four major macromolecules are carbohydrates, lipids, proteins, and nucleic acids.
- Structure determines function: the 3D arrangement of a macromolecule affects its biological role.
Carbohydrates
- Carbohydrates are made from monosaccharides (monomer units like glucose, fructose, galactose).
- Monosaccharides join by dehydration reactions to form disaccharides and polysaccharides.
- Cellulose (in plants) consists of strong, linear chains for cell wall protection, not energy storage.
- Amylose (coiled) and amylopectin (branched) store glucose in plants; glycogen (branched) stores glucose in animals.
- Branched and coiled structures allow compact glucose storage for energy.
Proteins
- Proteins are composed of 20 different amino acids joined by peptide bonds (dehydration reaction).
- Each amino acid has an amino group, carboxyl group, hydrogen, and variable R group.
- Primary structure: sequence of amino acids connected by peptide bonds.
- Secondary structure: alpha helices and beta sheets stabilized by hydrogen bonds between backbone atoms.
- Tertiary structure: overall 3D folding caused by R group interactions (hydrophobic, ionic, disulfide bridges, hydrogen bonds).
- Quaternary structure: multiple polypeptide chains assembled together (e.g., hemoglobin).
- Enzyme function depends on the integrity of the active site; structure changes can stop enzymatic activity.
Nucleic Acids
- Nucleic acids (DNA and RNA) are made of nucleotide monomers (phosphate group, five-carbon sugar, nitrogenous base).
- DNA uses deoxyribose and bases A, T, G, C; RNA uses ribose and A, U, G, C.
- Nucleic acid strands extend from the 5’ end to the 3’ end; new nucleotides add at the 3’ end by dehydration reactions.
- DNA is double-stranded and antiparallel for stability; mRNA is single-stranded and transient.
- Base pairing: A-T (or A-U in RNA) with 2 hydrogen bonds; G-C with 3 hydrogen bonds; ensures genetic information is preserved.
Lipids
- Lipids are primarily non-polar macromolecules, distinguished by long fatty acid chains.
- Phospholipids have a hydrophilic (polar) head and hydrophobic (non-polar) tails, crucial for cell membranes.
- Phospholipids self-assemble into bilayers, liposomes, and micelles based on their structure.
- Fatty acids can be saturated (rigid, less fluid) or unsaturated (kinked tails, more fluid), affecting membrane properties.
- Membrane flexibility is vital in cold environments to prevent cellular damage.
Key Terms & Definitions
- Monosaccharide — Single sugar unit; monomer of carbohydrates.
- Dehydration reaction — Chemical reaction that joins monomers by removing water.
- Peptide bond — Covalent bond joining amino acids in proteins.
- Primary structure — Linear sequence of amino acids in a protein.
- Secondary structure — Local folding (alpha helix, beta sheet) in proteins via hydrogen bonds.
- Tertiary structure — Overall 3D protein folding due to R group interactions.
- Quaternary structure — Association of multiple protein subunits.
- Nucleotide — Monomer of nucleic acids (phosphate, sugar, base).
- Antiparallel — DNA strands running in opposite 5’ to 3’ directions.
- Phospholipid — Lipid with hydrophilic head and hydrophobic tails; forms cell membranes.
Action Items / Next Steps
- Review notes on macromolecules’ structure and function.
- Prepare for review games and AP test practice next week.