Protein structure/function relationships

The sequence of DNA bases is unique to a particular gene, and this nucleotide sequence will encode the specific amino acid sequence of a given protein. All proteins are comprised of 20 standard amino acids, and each amino acids is encoded by at least one specific three base sequence of DNA called a codon. Therefore a sequence of codons at the level of DNA will determine the sequence of amino acids in a protein. The sequence the amino acid sequence of a protein is crucial in the determination of the three-dimensional structure of that protein which in turn determines its function. If we can find a way of altering that three-dimensional structure than we have a powerful tool which can be used to alter the function of a protein. 

Each amino acid has a particular physical-chemical property, such as electrostatic charge or hydrophobicity. When amino acids form polymers, each amino acid in the sequence will contribute to the determination of the three-dimensional structure of that particular protein. The rules which determine how a linear sequence of amino acids folds up to form a functional protein are a long way from being understood, and are currently the subject of much of intense basic research efforts. Even though the actual details of the protein-folding rules are unknown, the basic principle that a sequence of amino acids determines the three-dimensional structure is a well-founded. Individual proteins can be unfolded to form nonfunctional polypeptide chains, but these unfolded proteins can be refolded to format active proteinsin the absence of any external help. This is very strong evidence which suggests that the physico-chemical properties in a sequence of amino acids are sufficient to determine the specific folding of an amino acid chain to form a functional protein.

Each single protein molecule in every living cell is encoded by the DNA, and every single protein goes through the process folding to determine its specific three-dimensional structure. In a cell, all the copies of a particular protein have the same three-dimensional structure, and it is the exact protein structure which determines the specific function of a protein.