Proteins are complex molecules found in all living organisms, playing many roles fundamental to life. They are made of smaller units called amino acids, linked in long chains. 20 types of amino acids combine in various sequences to create unique proteins. Each protein’s specific three-dimensional structure relates directly to its role within a cell or organism.
Proteins and Their Diverse Functions
Proteins perform diverse functions within the body, essential for the structure, operation, and regulation of cells, tissues, and organs. Different types are specialized for distinct biological roles.
Enzymatic proteins function as biological catalysts, accelerating chemical reactions within cells without being consumed. Amylase, found in saliva, helps initiate the digestion of starches into simpler sugars. Pepsin, another digestive enzyme, breaks down proteins into smaller units in the stomach.
Structural proteins provide support and shape to cells, tissues, and organs, contributing to the body’s framework. Collagen, the most abundant protein in mammals, provides strength to bones, skin, tendons, and ligaments. Keratin is another significant structural protein, forming the primary component of hair, nails, and the outer layer of skin, offering protection and rigidity.
Transport proteins are responsible for moving substances throughout the body or across cell membranes. Hemoglobin, found in red blood cells, transports oxygen from the lungs to various tissues and organs. Albumin, a protein in blood plasma, helps carry fatty acids, hormones, and some medicines, while also maintaining fluid balance.
Hormonal proteins act as chemical messengers, transmitting signals between different cells, tissues, and organs to coordinate biological processes. Insulin, for instance, is a protein hormone produced by the pancreas that regulates blood glucose levels by signaling cells to absorb sugar from the bloodstream. Growth hormone, secreted by the pituitary gland, promotes tissue growth and repair.
Defensive proteins protect the body against foreign invaders and harm. Antibodies, also known as immunoglobulins, are specialized proteins produced by the immune system that identify and neutralize harmful substances like bacteria and viruses.
Contractile proteins are responsible for muscle movement, enabling actions like walking, running, and even the beating of the heart. Actin and myosin are two primary contractile proteins that work together in muscle cells. They interact by sliding, causing muscle fibers to shorten and generate force.
Proteins in Our Daily Diet
Sufficient dietary protein is essential for growth, cell repair, and proper body function. The body uses amino acids from dietary protein to build new proteins (e.g., in muscles and bones) and create compounds like enzymes and hormones. Dietary protein also supplies essential amino acids, which the body cannot produce and must obtain from food.
Foods provide protein from both animal and plant sources. Animal sources include lean meats (beef, lamb, poultry), fish, seafood, eggs, and dairy products (milk, yogurt, cheese). These often contain all nine essential amino acids.
Plant-based protein sources are abundant and contribute to daily intake. Examples include legumes (beans, lentils, chickpeas), nuts, seeds, whole grains (quinoa), and soy products (tofu, tempeh, edamame). A varied diet ensures all necessary amino acids.