![]() The secondary structure consists of local packing of polypeptide chain into α-helices and β-sheets due to hydrogen bonds between peptide bond – central carbon backbone. Primary structure refers to the linear sequence of the amino acids connected by the peptide bonds. Proteins have four levels of organization. Since the sequence of the amino acids is contingent on the genetic code, the shape of the protein is encoded in the DNA. The 3D conformation of the protein depends on the interactions between amino acids in the polypeptide chain. In short, the better fit between two molecules, the better it functions, the more bonds can be made, the faster the signal can pass, or the stronger two molecules connect (think adhesion molecules). ![]() The change of enzymatic pocket, due to mutation or modification of an amino acid residue changes the affinity and/or specificity of the enzyme. The best known example of the shape-function relationship is the “key and lock” theory of enzymatic function. ![]() The precise shape of the domain, resulting from the presence of non covalent bonds between residues in a polypeptide chain decides about the function. They are modular in nature and their interactions with other molecules in the cell rely on the presence of specific functional domains. Proteins are the building blocks of cell structures and motors of cellular activities. ![]() 3 Four levels of protein structure Protein structure and function ![]()
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