Biological Macromolecules Overview

Overview

This lecture reviews the four main types of biological macromolecules, their structures, functions, monomers, and related concepts, with emphasis on their exam-relevant features and differences.

Types of Macromolecules

• The four types of biological macromolecules are carbohydrates, lipids, proteins, and nucleic acids.
• Carbohydrates have the empirical formula (CH₂O)ₙ and include sugars and starches.
• Lipids include triglycerides, fatty acids, steroids, and phospholipids; generally hydrophobic.
• Proteins are polymers of amino acids and perform many cellular functions.
• Nucleic acids (DNA and RNA) store and transmit genetic information.

Carbohydrates

• Monosaccharides are single sugar units (e.g., glucose, fructose, galactose, ribose).
• Glucose is an aldohexose; fructose is a ketohexose; galactose is a C4 epimer of glucose.
• Disaccharides consist of two sugar units (e.g., sucrose, lactose, maltose).
• Polysaccharides (starch, glycogen, cellulose, chitin) have structural or storage roles.

Lipids

• Most lipids are nonpolar and not soluble in water.
• Triglycerides are for long-term energy storage; composed of glycerol + 3 fatty acids.
• Phospholipids form cell membranes; have a polar head and two nonpolar tails (one saturated, one unsaturated).
• Steroids (e.g., cholesterol, testosterone) have four fused rings.
• Chitin is the structural polysaccharide in insects; cellulose for plants.

Proteins & Amino Acids

• Amino acids are the monomers of proteins; general structure: central carbon, amino group, carboxyl group, hydrogen, and R group.
• Peptide bonds are formed between amino acids via dehydration synthesis (loss of water).
• Proteins have four levels of structure: primary (sequence), secondary (α-helix, β-sheet), tertiary (folding), quaternary (multiple chains).
• Some amino acids are nonpolar/aromatic (e.g., phenylalanine).
• Enzymes (end in "-ase") are proteins that speed up chemical reactions.

Nucleic Acids

• Nucleotides are the monomers; consist of a phosphate group, ribose sugar, and nitrogenous base.
• Pyrimidines: thymine, cytosine, uracil (one ring); Purines: adenine, guanine (two rings).
• DNA and RNA differ at carbon 2 in the sugar; DNA has H, RNA has OH.

Key Terms & Definitions

• Monosaccharide — Single sugar unit, e.g., glucose.
• Polysaccharide — Many sugar units; e.g., starch, glycogen.
• Peptide Bond — Covalent bond between amino acids formed by dehydration synthesis.
• Phospholipid — Lipid forming cell membranes, with hydrophilic head and hydrophobic tails.
• Steroid — Lipid with four fused rings.
• Enzyme — Protein that catalyzes reactions, usually ending in "-ase".
• Pyrimidine — Nitrogenous base with one ring (thymine, cytosine, uracil).
• Purine — Nitrogenous base with two rings (adenine, guanine).

Action Items / Next Steps

• Review core structures of each macromolecule type.
• Memorize differences between α and β glycosidic linkages.
• Practice identifying monomers and functional groups.
• Study major disaccharides and the structure of phospholipids.
• Know examples of enzymes, proteins, and non-protein molecules.