proteini

Proteins are large, complex biomolecules essential for nearly all biological processes. They are polymers of amino acids linked by peptide bonds, folded into three-dimensional structures that determine their functions. The sequence of amino acids—the primary structure—governs how the chain folds into secondary, tertiary, and, for multi-chain proteins, quaternary structures.

Proteins are broadly categorized as fibrous (structural, like collagen and keratin) or globular (enzymes, transport proteins, antibodies). They perform roles including catalysis, support, movement, signaling, transport, immune defense, and regulation of metabolism.

Biosynthesis begins with gene transcription and mRNA translation at ribosomes. After synthesis, proteins may undergo post-translational modifications (phosphorylation, glycosylation, folding assistance by chaperones) that affect activity and localization. The proteome of a cell or organism refers to its complete set of proteins.

In nutrition, proteins supply amino acids. Essential amino acids must be obtained from the diet. Complete proteins provide all essential amino acids in adequate proportions (e.g., most animal proteins; many plant proteins when diversified). Digestion uses proteases such as pepsin, trypsin, and chymotrypsin to cleave proteins into amino acids and di- or tri-peptides absorbed in the small intestine.

Common examples include enzymes like amylase and lactase; structural proteins such as collagen; transport proteins like hemoglobin; and regulatory proteins such as insulin and glycogen synthase.

Proteins are studied in proteomics, a field that maps and quantifies the protein complement of a cell, tissue, or organism, often using mass spectrometry and bioinformatics.