biomoleculesproteins

Proteins are biomolecules composed of one or more long chains of amino acids. They perform a vast array of functions essential to living organisms. The sequence of amino acids determines a protein’s properties and ultimately its three-dimensional structure, which enables specificity in catalysis, binding, and regulation.

Proteins exhibit four levels of structure: primary (amino acid sequence), secondary (local structures such as alpha helices and beta sheets), tertiary (overall 3D folding of a single polypeptide), and quaternary (assembly of multiple polypeptides). The structure is stabilized by hydrogen bonds, ionic interactions, hydrophobic effects, and disulfide bonds. Protein folding is guided by chaperone proteins and may be affected by pH, temperature, and solvents. Denaturation disrupts structure and function.

Classes include enzymes, structural proteins, transport proteins, signaling molecules, antibodies, and membrane proteins. Proteins can be fibrous (structural, e.g., collagen, keratin) or globular (enzymes and many soluble proteins). They are synthesized by ribosomes in a process dictated by genetic information, translated from mRNA, and often undergo post-translational modifications such as phosphorylation, glycosylation, or cleavage. Degradation via proteolysis regulates activity and turnover.

Because of their central role, proteins are targets in medicine and industry. Enzymes catalyze reactions, antibodies defend against pathogens, and hormones regulate physiology. Protein structure determination uses techniques such as X-ray crystallography, nuclear magnetic resonance, and cryo-electron microscopy. Dysfunctions in proteins can lead to diseases including misfolding disorders and metabolic conditions.