One of the smallest protein molecules is insulin, and the largest being Titin which consist of 34,350 amino acids. It actually depends on the number of polypeptide molecules it contains. Now one or more of these polypeptide chains twist or fold spontaneously and a protein is formed. These amino acids are connected together with peptide bonds, and a few such bonds linking together form a polypeptide chain. What this actually entails is that proteins are long chain-like structure, with amino acids being the main ingredient. Now we previously learnt that amino acids are the building blocks of proteins. A selected number of examples are given to illustrate the power of the techniques in applications of biological interest.Proteins are what we call biological polymers (i.e. These data, together with sophisticated molecular modeling techniques, allow for refinement of protein structural models as well as rapid assessment of conformational changes resulting from ligand binding or macromolecular interactions. However, the chemical shifts must first be assigned to particular residues, making the technique considerably slower than the optical methods. NMR chemical shifts may also be used to determine the positions of secondary structure within the primary sequence of a protein. The frequencies of amide bands are analyzed to determine the distribution of secondary structures in proteins. Infrared (IR) and Raman spectroscopy require only small volumes of protein solution. Both CD and Raman spectroscopies are particularly useful for measurements over a range of temperatures. Circular dichroism (CD) spectroscopy provides rapid determinations of protein secondary structure with dilute solutions and a way to rapidly assess conformational changes resulting from addition of ligands. Several methods for determination of the secondary structure of proteins by spectroscopic measurements are reviewed.
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