Organic molecules, the building blocks of life, are defined by the presence of carbon (C). In most cases, each carbon atom bonds with hydrogen (H) or oxygen (O). Nitrogen (N) is also common, especially in proteins and nucleic acids.
These macromolecules are typically large, comprising hundreds to thousands of atoms. Carbon’s tetravalency allows it to form diverse backbones—linear, cyclic, or branched—making it the core of organic chemistry.
Water solubility varies widely. For example, the fatty acids that make up lipids are hydrophobic, resisting water, whereas many sugars dissolve readily. Roughly one‑third of the human body mass is made up of organic molecules.
DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) are the only nucleic acids found in nature. Their sugar backbones—deoxyribose in DNA and ribose in RNA—differ by a single oxygen atom. DNA’s double helix stores the genetic code, while RNA exists in three primary forms. Messenger RNA (mRNA) carries instructions from DNA to ribosomes, where proteins are synthesized.
Carbohydrates collectively represent the most abundant class of organic molecules on the planet. Their role spans basic cellular nutrition to structural support in plants. All carbohydrates share the ratio of two hydrogens for every oxygen and carbon atom, giving the general formula (CH₂O)ₙ. Simple sugars such as glucose (C₆H₁₂O₆), fructose, and galactose are monosaccharides. When linked together, they form polysaccharides like glycogen—an energy store in muscle and liver—and cellulose, a structural component of plant cell walls that humans cannot digest.
Lipids account for 15–20 % of lean body mass, making them a significant component even in individuals with minimal fat tissue. They contain a high proportion of carbon and hydrogen relative to oxygen, which explains their hydrophobic nature. Dietary fats, known as triglycerides, consist of a glycerol backbone bonded to three fatty acids, which can be saturated or unsaturated.
Proteins are the most varied macromolecules, providing structural support and catalyzing biochemical reactions. They are assembled from 20 standard amino acids, each containing nitrogen. Translation of mRNA by ribosomes, aided by transfer RNA (tRNA), produces polypeptide chains that fold into functional proteins.
For deeper insights into each class, refer to reputable scientific resources.
