proteiinin

Proteiini (Finnish for protein) is a large, diverse class of biomolecules essential to nearly all physiological processes. Proteins are polymers of amino acids folded into unique three-dimensional structures that determine their functions. They are encoded by genes and synthesized by ribosomes through translation of messenger RNA.

Amino acids are linked by peptide bonds to form polypeptide chains. The sequence of amino acids (the primary structure) dictates how the chain folds into secondary structures such as alpha helices and beta sheets, which further fold into tertiary and, for some proteins, quaternary structures. Proteins can be fibrous (structural, e.g., collagen, keratin) or globular (enzymes, transport proteins). Many proteins require cofactors or prosthetic groups to be functional.

Biosynthesis begins with transcription of genes into mRNA, followed by translation at ribosomes. After synthesis, proteins may undergo post-translational modifications (phosphorylation, glycosylation, etc.) that modulate activity, localization, or stability. Protein turnover involves selective degradation by proteolytic systems.

Proteins perform a wide range of roles: enzymes accelerate chemical reactions; structural components provide support; transport and storage proteins move molecules or ions; signaling proteins regulate cellular processes; antibodies defend against pathogens. Nutritionally, dietary proteins supply essential amino acids not synthesized by the body. Most adults require about 0.8 grams per kilogram of body weight per day, with higher needs during growth or intense training. Protein quality varies with amino-acid composition and digestibility.

Origin of the term: the word protein was coined in the 1830s by Jöns Jakob Berzelius, from the Greek proteios meaning primary. The concept of proteins has since become central to biochemistry, physiology, and medicine.