Organic Molecules Overview

Overview

This lecture covers the major classes of organic molecules—carbohydrates, lipids, proteins, and nucleic acids—their structures, functions, and the chemical processes involved in their synthesis and breakdown.

Introduction to Organic Chemistry

• Organic compounds always contain carbon and are often large, complex molecules.
• Macromolecules (polymers) are built from repeating monomer subunits.
• Four major types: carbohydrates, lipids, proteins, nucleic acids.

Polymer Synthesis and Breakdown

• Dehydration synthesis joins monomers to form polymers, releasing water.
• Hydrolysis breaks polymers into monomers, requiring water input.
• Both reactions are catalyzed by enzymes.

Carbohydrates

• Three types: monosaccharides (single sugars), disaccharides (two sugars), polysaccharides (long chains).
• Monosaccharides (e.g., glucose, fructose) provide immediate energy and are directly absorbed.
• Disaccharides (e.g., sucrose, lactose) and polysaccharides are broken down by hydrolysis before absorption.
• Glycogen (animal storage) and starch (plant storage) are digestible polysaccharides; cellulose is not digestible but provides fiber.
• Carbohydrates also contribute to DNA/RNA backbone and cell surface signaling.

Lipids

• Lipids are water-insoluble molecules: main types are triglycerides, phospholipids, and steroids.
• Triglycerides (fats/oils): glycerol + 3 fatty acids, long-term energy storage, insulation, and organ protection.
• Saturated fats (solid, no double bonds) increase heart disease risk; unsaturated fats (liquid, double bonds) are healthier.
• Phospholipids have a hydrophilic head and hydrophobic tails, form the cell membrane bilayer.
• Steroids (e.g., cholesterol, estrogen, testosterone) have four carbon rings and regulate functions and membrane stability.

Proteins

• Proteins are polymers of amino acids linked by peptide bonds.
• Twenty amino acids; nine are essential and must come from the diet.
• Each amino acid has an amino group, carboxyl group, and unique R group.
• Structure levels: primary (sequence), secondary (hydrogen bonds—alpha helices/beta sheets), tertiary (3D folding), quaternary (multiple chains).
• Protein function depends on structure; mutations or denaturation can disrupt activity.
• Functions include structure (collagen, keratin), movement (actin, myosin), transport (hemoglobin), defense (antibodies), and catalysis (enzymes).

Enzymes

• Enzymes are protein catalysts that speed up biochemical reactions without being consumed.
• Each enzyme is specific to its substrate (e.g., lactase acts on lactose).
• Enzymes often end with "-ase".

Nucleic Acids and ATP

• Nucleic acids (DNA, RNA) are polymers of nucleotides (nitrogen base, pentose sugar, phosphate).
• DNA stores genetic information (adenine-thymine, guanine-cytosine pairs), is double-stranded, and in the nucleus.
• RNA acts as messenger, uses ribose sugar, uracil instead of thymine, and is single-stranded.
• ATP (adenosine triphosphate) is a single nucleotide that stores and releases energy for cellular work.

Key Terms & Definitions

• Monomer — a single building block unit of a polymer.
• Polymer — a large molecule made of repeating monomers.
• Dehydration synthesis — process joining two molecules with the removal of water.
• Hydrolysis — breaking a bond in a molecule using water.
• Monosaccharide — single sugar unit.
• Disaccharide — two monosaccharides joined together.
• Polysaccharide — long chain of monosaccharides.
• Triglyceride — fat molecule made of glycerol and three fatty acids.
• Phospholipid — lipid with a phosphate group, forms cell membranes.
• Steroid — lipid with four fused carbon rings.
• Amino acid — building block of proteins.
• Peptide bond — bond linking two amino acids.
• Enzyme — protein that catalyzes a specific biochemical reaction.
• Nucleotide — building block of nucleic acids.
• ATP — energy-carrying nucleotide used by cells.

Action Items / Next Steps

• Review & memorize the structural differences and functions of carbohydrates, lipids, proteins, and nucleic acids.
• Study the four levels of protein structure and why structure affects function.
• Learn the main differences between DNA and RNA.
• Prepare for next chapter on cells and genetic information flow.