Protein

Protein molecules are chains of amino acids that play many important roles in living systems. As far as is known, proteins have existed as long as life on earth has existed and are an essential ingredient in all cells. For most organisms, including humans, proteins must be ingested and digested in order to obtain essential nutrients that cannot be synthesized by the organism itself.

Synthesis

Main Article: Ribosome

In both eukaryotic and prokaryotic cells, proteins are manufactured in ribosomes, which are made up of two sub-units of specially folded strands of RNA as well as some small proteins. A eukaryotic ribosome (e.g., that of a human) is slightly larger than the prokaryotic ribosome (e.g., that of a bacterial cell), but the two perform essentially the same essential function. Ribosomes connect amino acids to each other via peptide bonds in order to form strings called polypeptides.

Structure

The sequence of amino acids is determined by the genetic code on DNA; the simple sequence of amino acids alone is referred to as a protein's primary structure. Different residual groups on the amino acids can interact with water or each other, sometimes linking to each other, forming a certain three-dimensional structure, such as an alpha helix or a beta sheet; localized three-dimensional structure is referred to as a protein's secondary structure. A protein's tertiary structure is the entire three-dimensional conformation of a given peptide. Quaternary structure exists in proteins that are made up of multiple peptides, and it is the entire three-dimensional structure of every peptide and the links between them.

Function

Proteins are used within organisms for an extremely vast array of functions, which include but are not limited to structure, sending and receiving messages, regulation of processes, and enzymes are proteins catalyze chemical reactions.

See Also

• Amino acid