Proteins are essential biomolecules that form part of the cells of all living organisms and play vital roles in bodily growth and the maintenance of physiological functions. Proteins are composed of small units called amino acids, which are linked together by peptide bonds to form long chains. There are twenty primary amino acids involved in protein synthesis, and their specific sequence and quantity vary from one protein to another; this arrangement determines the protein's shape and function within the body. While the body can produce some amino acids, "essential" amino acids must be obtained through diet. Proteins are found in animal sources—such as meat, fish, eggs, milk, and dairy products—as well as in plant sources like legumes, nuts, and grains. The nutritional value of a protein depends on the specific amino acids it contains and the body's ability to digest and utilize it. Proteins play a fundamental role in building muscles, skin, hair, nails, and various tissues, and they assist in repairing damaged cells and tissues by replacing them with new ones. Some proteins function as enzymes that accelerate biochemical reactions within the body, while others are involved in the formation of hormones that regulate processes such as growth and blood sugar levels. Antibodies are defensive proteins produced by the immune system to recognize and combat pathogens. Additionally, certain proteins facilitate the transport of substances within the body; for instance, hemoglobin transports oxygen through the bloodstream, while other proteins transport fats, vitamins, and minerals. There are structural proteins such as collagen, which supports the skin, bones, and tendons, and keratin, a component of hair and nails. Cell membrane proteins also facilitate the transport of substances, signal reception, and intercellular communication. Protein digestion begins in the stomach through the action of acid and enzymes and is completed in the small intestine. Following digestion, amino acids are absorbed into the bloodstream and transported to cells to be used in synthesizing new proteins. Unlike fats and carbohydrates, the body does not store protein; therefore, it must be consumed regularly as part of a balanced diet. Protein requirements vary based on age, weight, health status, and physical activity levels. Children, adolescents, pregnant women, and athletes require adequate amounts to support growth and tissue formation. Protein deficiency can lead to muscle weakness, stunted growth, impaired immunity, and slow wound healing. Conversely, excessive protein intake may cause health issues for some individuals, particularly those with kidney disease. Protein can serve as an energy source when carbohydrates and fats are insufficient, though it is not the preferred primary source of energy. Protein synthesis occurs within cells through the processes of transcription and translation, guided by information encoded in DNA. Genetic instructions are transferred from DNA to messenger RNA (mRNA), which is then read by ribosomes to assemble amino acids in the correct sequence. Once the protein chain is formed, it folds into a three-dimensional structure that enables it to perform its specific function. High temperatures or drastic changes in pH levels can alter a protein's shape and cause it to lose its function—a process known as protein denaturation. Proteins are utilized in numerous medical and industrial applications, such as the production of insulin, vaccines, and diagnostic or therapeutic enzymes. Furthermore, studying protein structure and function aids in understanding diseases and designing more precise medications. As proteins are essential for life, obtaining them from diverse sources in balanced quantities supports the body's health, growth, and ability to function normally.