Biomolecules

When you eat a meal, what happens to that food inside your body? It gets broken down into molecules — tiny particles that your cells can actually use. And your body itself is made of these same kinds of molecules. This chapter is about the chemical building blocks of life: the biomolecules. Carbohydrates, proteins, lipids, and nucleic acids — plus the enzymes that make everything work and the vitamins that keep everything running smoothly. Let us start with carbohydrates. The name comes from 'hydrate of carbon' because these molecules have a ratio of roughly one carbon to one water molecule (CH₂O)ₙ. Carbs are the most abundant biomolecules on Earth. Their primary function is to provide energy, but they also serve structural roles. Simple carbohydrates are monosaccharides — single sugar units like glucose, fructose, and galactose. Glucose is the most important monosaccharide because it is the primary fuel for cellular respiration. Two monosaccharides joined together make a disaccharide — sucrose (table sugar), lactose (milk sugar), and maltose. Complex carbohydrates (polysaccharides) are long chains of monosaccharides: starch (energy storage in plants), glycogen (energy storage in animals), and cellulose (structural component of plant cell walls). Cellulose is the most abundant organic molecule on Earth — and humans cannot digest it because we lack the enzyme cellulase. Proteins are the workhorses of the cell. They do almost everything: catalyze reactions (enzymes), provide structure (collagen in skin and bones), transport molecules (hemoglobin carries oxygen), defend the body (antibodies are proteins), regulate processes (insulin regulates blood sugar), and enable movement (actin and myosin in muscles). Proteins are made of amino acids linked together by peptide bonds. There are 20 standard amino acids, of which 9 are essential — they must come from your diet because your body cannot make them. Each amino acid has a central carbon bonded to an amino group (-NH₂), a carboxyl group (-COOH), a hydrogen atom, and a variable R group that gives each amino acid its unique properties. A protein's function depends entirely on its structure — from the sequence of amino acids (primary structure), how the chain folds locally (secondary structure — alpha helices and beta sheets), the overall three-dimensional shape (tertiary structure), and how multiple chains assemble (quaternary structure). If the shape changes, the protein stops working — this is what happens when you cook an egg; the proteins denature and the egg white turns solid. Lipids are a diverse group of hydrophobic molecules. Fats and oils store energy — fat contains about twice the calories per gram as carbohydrates. Phospholipids make up cell membranes. Steroids like cholesterol and hormones regulate body processes. Nucleic acids carry genetic information. DNA holds the genetic blueprint; RNA helps execute it. Both are made of nucleotides. And then there are enzymes — biological catalysts that speed up reactions without being consumed. Almost all enzymes are proteins. They work by lowering the activation energy of reactions. Their activity is affected by temperature, pH, and inhibitors. Vitamins and minerals are essential micronutrients that often act as helpers for enzymes. Understanding biomolecules is understanding the chemistry of life itself.