Carbon's Building Blocks: An Introduction to Organic Chemistry

Think about three things you might find in your kitchen: a teaspoon of sugar, a drop of sunflower oil, and a strip of chicken. Now think about the instructions inside every cell of your body — your DNA. These four things could not look or feel more different, yet they share one invisible feature. They are all built around the same atom: carbon. Chemists noticed centuries ago that most substances made by living things contain carbon. They called this branch of science 'organic chemistry' — the chemistry of carbon-containing compounds. Today you are going to find out why carbon is such an extraordinary atom, and how it builds the molecules that make life possible.

Organic chemistry is the study of compounds that contain carbon–hydrogen bonds. Almost all molecules made by, or found in, living organisms are organic compounds. Why carbon? Carbon has four bonding 'hands' — it can form four covalent bonds at once. A covalent bond is when two atoms share electrons to stay connected. Because carbon has four of these bonds available, it can link to other carbon atoms in long chains, rings, and branching structures. No other common element can do this as flexibly. This gives carbon the power to build millions of different molecules. Biochemists group the organic molecules of living things into four main classes. Think of these as the four construction materials of life. 1. Carbohydrates — Your Quick-Energy Fuel Carbohydrates are made of carbon, hydrogen, and oxygen, usually in a ratio that gives them the formula (CH₂O)ₙ. Simple carbohydrates, called sugars (such as glucose), dissolve easily and release energy quickly. Complex carbohydrates, like starch and cellulose, are long chains of sugars. When you eat a slice of bread, your body breaks down the starch into glucose to power your cells. Cellulose, found in plant cell walls, gives plants their rigid structure — it is what makes a carrot crunchy. 2. Lipids — Long-Term Energy and More Lipids include fats, oils, and waxes. They are made mostly of carbon and hydrogen, with very little oxygen. Because lipids pack a lot of energy into a small space, your body stores spare energy as fat. Lipids also build cell membranes — the thin, flexible boundary around every cell in your body — and act as chemical messengers (hormones). The olive oil in a salad dressing is a lipid. 3. Proteins — The Workers of the Cell Proteins are large, complex molecules built from smaller units called amino acids. There are 20 different amino acids, and the order in which they are joined determines what a protein does. Proteins carry out almost every task in a living organism: enzymes speed up chemical reactions, haemoglobin carries oxygen in your blood, keratin makes your hair and nails strong, and antibodies defend you against infection. 4. Nucleic Acids — The Instructions Nucleic acids store and transmit genetic information. DNA (deoxyribonucleic acid) holds the instructions for building every protein your body makes. RNA (ribonucleic acid) carries those instructions from the DNA to the cell's protein-making machinery. Nucleic acids are built from units called nucleotides, each containing a sugar, a phosphate group, and a nitrogen-containing base.