Macromolecules are large molecules fundamental to all living organisms. They form essential structures and perform diverse functions for cells and tissues. These molecules are polymers, built from repeating units called monomers. Four main types are crucial for life.
Carbohydrates: Energy and Structure
Carbohydrates are macromolecules composed of carbon, hydrogen, and oxygen atoms. Their building blocks are sugar units called monosaccharides, like glucose, a primary energy source. Monosaccharides link to form disaccharides, like sucrose, or long chains (polysaccharides). Polysaccharides include starch and glycogen, serving as energy storage molecules in plants and animals, respectively.
Beyond energy storage, carbohydrates also have structural roles. Cellulose provides structural support in plant cell walls. Chitin, another structural polysaccharide, is found in insect and crustacean exoskeletons. Some carbohydrates are also involved in cell recognition and signaling on cell surfaces.
Lipids: Versatile Energy Storage and Barriers
Lipids are diverse molecules, insoluble in water due to their nonpolar nature. They perform various functions, including long-term energy storage, like fats and oils. Common lipids like triglycerides are stored in adipose cells, serving as concentrated energy reserves.
Lipids form cell membranes. Phospholipids, with hydrophilic heads and hydrophobic tails, arrange into a lipid bilayer. This bilayer creates a selective barrier, controlling substance movement into and out of cells. Steroids, another lipid, function as chemical messengers, including hormones like testosterone and estrogen, regulating bodily processes.
Proteins: The Body’s Workhorses
Proteins are versatile macromolecules made of amino acids linked in long chains. Their specific amino acid sequence determines a protein’s unique three-dimensional shape, directly related to its function. Proteins perform diverse roles within living organisms, often acting as primary functional molecules.
Many proteins function as enzymes, accelerating most chemical reactions, like digestion. Other proteins provide structural support, like collagen in connective tissues or keratin in hair. Proteins also facilitate transport, such as hemoglobin carrying oxygen in the blood, and aid in defense, with antibodies protecting against foreign invaders. They also serve as messengers, like hormones, transmitting signals between cells.
Nucleic Acids: The Blueprint of Life
Nucleic acids are the primary information-carrying molecules in cells. They are polymers made of repeating nucleotides. Each nucleotide has a sugar, a phosphate group, and a nitrogen-containing base. The two main types are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).
DNA is the genetic material found in all free-living organisms and most viruses, containing instructions for building and maintaining organisms. It typically forms a double helix structure with two paired nucleotide strands. RNA carries out these instructions, assisting in protein synthesis. Messenger RNA (mRNA) acts as a temporary copy of genetic information from DNA, while other RNA types, like ribosomal RNA (rRNA) and transfer RNA (tRNA), translate this information into proteins.