A protein is a long chain or polymer of amino acids. The sequence and the three-dimensional shape of amino acid residues determine the function. As well as multiples forms present in various tissues. Proteins also have several functions inside cells. Such as enzymes that catalyze metabolic reactions, antibodies that provide immunity to infection. And transport molecules that carry other molecules that form part of the machinery that reads the genetic code.

Amino Acid is a chemical building block of protein. Amino acids have an amine group, a carboxylic acid group, and a side chain attached to the alpha carbon atom. There are 20 standard amino acids that are incorporated into proteins during the translation of mRNA by living cells. The set of amino acids used in protein synthesis are known as proteinogenic or natural amino acids.

Some proteins are involved with making energy by oxidizing food molecules in mitochondria for cellular respiration. Others transport carbon dioxide in the blood to be exhaled by the respiratory system. Proteins are also needed to make muscle fibers contract or let skeletal muscles relax. Proteins help maintain the structure of cell membranes and transport molecules across those membranes.

Proteins also have structural or mechanical functions. Such as actin and myosin in muscle and the proteins in the cytoskeleton. Natural proteins have their own set of rules. They may contain “non-natural” stereoisomers, which are structural isomers that differ only in the way the atoms are arranged in space. Proteins also contain less common types of non-carbon bonds, which can be in the form of sulfur-containing cysteine.

Although purifying protein means taking away other things that are in them. There are lots of ways to purify proteins. Such as ultracentrifugation, precipitation, electrophoresis, and chromatography. And the method which generally used to study the structure or function of protein includes immunohistochemistry, site-directed mutagenesis, X-ray crystallography, nuclear magnetic resonance, and mass spectrometry.