próteini

Próteini are large biomolecules essential to nearly every biological process. They are polymers built from amino acids and perform structural, catalytic, signaling and regulatory roles in all living organisms. The word "próteini" is used in some languages to refer to these molecules.

They are composed of one or more polypeptide chains folded into unique three-dimensional structures. The sequence of amino acids determines the chain's properties. Proteins exhibit four levels of structure: primary, secondary (a-helix, beta sheets), tertiary (three-dimensional fold), and quaternary (assembly of multiple chains).

Functions include enzymes that accelerate chemical reactions, structural proteins that provide scaffolding (collagen, keratin), transport proteins such as hemoglobin, signaling molecules like insulin, immune components like antibodies, and motors such as actin and myosin. They also serve in storage and defense.

Synthesis begins with gene transcription and mRNA translation on ribosomes, followed by post-translational modifications (phosphorylation, glycosylation, cleavage). Dietary proteins are digested into amino acids and small peptides, which the body uses to synthesize new proteins. Recommended intake varies; adequate essential amino acids are required for growth and maintenance.

Protein diversity is immense: fibrous proteins for structure, globular proteins for catalysis and regulation, membrane proteins, and multi-subunit complexes. Proteins are studied in proteomics and biotechnology, and many therapeutic proteins and antibodies are produced recombinantly.

The term protein was coined in the 1830s–1840s by Jöns Jakob Berzelius, reflecting the notion of a fundamental ingredient of life.