Proteins are essential molecules in our bodies, made up of smaller building blocks called amino acids. Each amino acid contains an amino group, a carboxyl group, and a unique side chain that determines its properties. These amino acids link together through peptide bonds to form long protein chains.
Proteins have four levels of structural organization. Primary structure is the sequence of amino acids. Secondary structure includes alpha helices and beta sheets. Tertiary structure is the overall three-dimensional folding, and quaternary structure involves multiple protein chains working together.
Proteins can be classified into six major functional categories based on their primary roles in the body. Enzymes act as biological catalysts, speeding up chemical reactions. Structural proteins like collagen provide support and shape to tissues. Transport proteins such as hemoglobin carry substances throughout the body.
Storage proteins store amino acids and other materials for later use. Hormonal proteins like insulin act as chemical messengers, coordinating body functions. Defensive proteins including antibodies protect us from pathogens and foreign substances. Each category has specialized structures that enable their specific functions.
Enzymes function as biological catalysts by binding to specific substrates at their active sites. The traditional lock-and-key model suggests that enzymes have rigid structures that perfectly match their substrates, like a key fitting into a lock.
The more accurate induced fit model shows that enzymes are flexible and change shape when substrates bind. This creates the optimal environment for catalysis. The catalytic cycle involves substrate binding, transition state formation, product formation, and product release. Enzymes like pepsin aid digestion, while catalase breaks down harmful peroxides.
Transport proteins like hemoglobin are essential for moving substances throughout the body. Hemoglobin consists of four subunits, each containing a heme group with an iron center that binds oxygen. The cooperative binding mechanism allows efficient oxygen pickup in the lungs and release in tissues where it's needed.
Structural proteins provide support and shape to our bodies. Collagen forms a strong triple helix structure that gives strength to connective tissues. Keratin creates protective barriers in hair, nails, and skin. Elastin allows tissues to stretch and return to their original shape. Actin and myosin filaments work together to enable muscle contraction and movement.
Protein hormones function as chemical messengers that coordinate body functions through complex communication networks. These hormones are released by endocrine glands, travel through the bloodstream, and bind to specific receptors on target cells using a lock-and-key mechanism that ensures precise signaling.
Insulin demonstrates how protein hormones regulate metabolism by controlling glucose uptake into cells. Growth hormone stimulates cell division and tissue growth throughout the body. Thyroid-stimulating hormone regulates metabolic rate by controlling thyroid function. These hormones trigger signal cascades that amplify their effects, allowing small amounts of hormone to produce large cellular responses.