Polypeptides of defined sequencePresentation Transcript
What are proteins? - complex natural compound: a complex natural substance that has a globular or fibrous structure composed of linked amino acids. Proteins are essential to the structure and function of all living cells and viruses. Proteins are not just polypeptides, they are polypeptides of defined sequence.
Meaning, every protein has a defined order of amino acid residues. As with the nucleic acids, this sequence is referred to as the primary structure of the protein.
When a living cell makes protein, the carboxyl group of one amino acid is linked to the amino group of another to form a peptide bond. The carboxyl group of the second amino acid is similarly linked to the amino group of a third, and so on, until a long chain is produced.
This chainlike molecule, which may contain from 50 to several hundred amino acid subunits, is called a polypeptide. A protein may be formed of a single polypeptide chain, or it may consist of several such chains held together by weak molecular bonds.
Each protein is formed according to a precise set of instructions contained within the nucleic, which is the genetic material of the cell. These instructions determine which of the 20 standard amino acids are to be incorporated into the protein, and in what sequence.
The R groups of the amino acid subunits determine the final shape of the protein and its chemical properties; an extraordinary variety of proteins can be produced from the same 20 subunits.