Biomolecules are organic molecules produced by living organisms necessary for sustaining life. These complex chemical compounds form the physical structures of cells and perform the chemical reactions required for growth, energy production, and reproduction. All biomolecules are considered organic because they are built around a framework of carbon atoms. The presence of carbon allows for the creation of the large, intricate molecular shapes that give these substances their diverse biological functions.
The Basic Components of Life
The vast complexity of biological structures is constructed from a small set of repeating molecular units. To build their large structures, most biomolecules rely on small building blocks called monomers. These individual units are chemically linked together in long chains to form polymers, which are the large macromolecules found in cells.
Carbon is the foundational element for these structures due to its unique atomic configuration, known as tetravalence. Carbon atoms can form four stable covalent bonds, allowing them to link together in endless combinations of straight chains, branched structures, and rings. This bonding flexibility permits the chemical diversity required to support all known forms of life.
Carbohydrates
Carbohydrates are a group of biomolecules that includes sugars, starches, and fiber, and their primary role is providing energy. These molecules are characterized by a chemical composition that approximates a 1:2:1 ratio of carbon, hydrogen, and oxygen atoms. The simplest form is a monosaccharide, or “simple sugar,” with glucose being the most recognized example, serving as the immediate fuel source for cellular respiration.
When two monosaccharides join, they form a disaccharide, such as sucrose. Complex carbohydrates, or polysaccharides, are long polymers made of many sugar units bonded together. Starch is the primary form of energy storage in plants, while cellulose provides rigid structural support to plant cell walls. These large chains must be broken down into simple sugars before the body can utilize them for energy.
Lipids
Lipids are a diverse group of compounds defined by their hydrophobic nature, meaning they repel water. This characteristic arises from their long hydrocarbon chains, which are nonpolar and do not mix with the polar water molecules. Lipids serve multiple functions, including acting as an efficient form of long-term energy storage.
Fats and oils, known chemically as triglycerides, store roughly twice the energy per gram compared to carbohydrates. Phospholipids are the fundamental structural components of all cellular membranes. These molecules have a hydrophilic “head” and two hydrophobic “tails,” causing them to spontaneously form a double layer that separates the cell’s interior from its external environment. Steroids, such as cholesterol and certain hormones, are also lipids, distinguished by their four-ring carbon structure, and function in signaling and maintaining membrane fluidity.
Proteins
Proteins carry out the vast majority of biological processes in the cell. These molecules are polymers built from smaller monomer units called amino acids. There are 20 common types of amino acids, and the sequence in which they are linked determines the protein’s specific structure and function.
The linear chain of amino acids, known as the primary structure, spontaneously folds into a precise three-dimensional shape, a process called protein folding. This final, intricate shape determines the protein’s activity; if the shape is altered, the function is usually lost. Proteins perform many roles, including acting as enzymes, which catalyze chemical reactions without being consumed. Structural proteins like keratin in hair and collagen in connective tissues provide physical support to the body. Proteins also serve in transport, moving substances like oxygen (hemoglobin) and other molecules across cell membranes or throughout the body.
Nucleic Acids
Nucleic acids are responsible for storing, transmitting, and expressing genetic instructions. These polymers are constructed from monomers known as nucleotides, which consist of a sugar, a phosphate group, and a nitrogenous base. The two main types are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).
DNA serves as the long-term genetic blueprint for the cell, containing the inherited instructions necessary for building all the organism’s proteins. It achieves this by forming a stable, double-stranded helix structure where the sequence of bases encodes the genetic information. RNA acts as the messenger and translator of these instructions, carrying copies of the genetic code from the DNA to the cellular machinery that synthesizes proteins. This flow of information from DNA to RNA to protein is the central mechanism for the continuity of life.