Proteins and their Structure

proteins and their structure in this module you will learn about proteins and their structure it is often said that we should include protein-rich food in our diet proteins are present in many food items such as eggs fish and milk proteins are not just present in foods they are also an integral part of our body they are present in our hair muscles and even in hemoglobin proteins are formed when a large number of amino acids born together through peptide bond depending upon the molecular shape of proteins they can be classified as fibrous proteins and globular proteins

let us study about them one by one fibrous proteins are formed when polypeptide chains run parallel to each other and are linked together to form fibers the molecules of these chains at many points are held together by hydrogen and disulfide bonds these proteins are insoluble in water some common examples of fibrous proteins are collagen and keratin on the other hand globular proteins are formed due to the folding a round of polypeptide chains this gives us spherical shape to the globular proteins these proteins are soluble in water some examples of globular proteins are insulin and albumin

as you can see the structure of proteins is quite complex let us study about this complex structure of proteins in detail we can study the structure of proteins in four different levels that is primary secondary tertiary and quaternary structure of proteins as we already know a protein is made of a large number of amino acids although there are only 20 amino acids but these amino acids linked together in different sequences giving rise to different polypeptide chains the sequence of amino acids in a polypeptide chain of a protein is called its primary structure if the sequence

of these amino acids has changed a new protein gets formed now secondary structure of proteins refers to the manner or shape in which the polypeptide chains are arranged the different arrangement of polypeptide chains exist due to the hydrogen bonding between the oxygen of carbon L of one amino acid to the hydrogen of the amide group of another amino acid the secondary structure shown right now is called alpha helix structure as you can see in this structure the hydrogen bonding is intermolecular that occurs between the amino acids of adjacent turns this results in the twisting up

of the structure into a right-handed spiral structure another type of secondary structure is formed when the polypeptide chains are stretched to the maximum extension and are then so folded that different strands lie alongside each other this type of structure is called beta pleated structure the different strands are held together by intermolecular hydrogen bonding between the amino acids of two different strands this structure looks similar to the pleated folds of drapery therefore it is known as beta pleated sheet structure so alpha helix structure and beta pleated sheet structure represents two different types of secondary structures of

proteins the further folding of the secondary structure of proteins gives rise to the tertiary structure of proteins therefore the tertiary structure represents the overall folding and coiling of the peptide chains it is the tertiary structure of a protein that gives a geometric shape to the protein that can be a fibrous or globular shape although many proteins consist of a single polypeptide chain there are some proteins which consist of two or more polypeptide chains these polypeptide chains are referred to as the subunits the quaternary structure is the special arrangement of these subunits with respect to each

other in the protein structure these subunits in a quaternary structure may be similar or different so we have seen that proteins are specific in their structure other than this proteins are specific in their biological activity to the natural state in which a protein occurs is its native state and a protein in its native state is called a native protein a native protein is highly stable however if a native protein is subjected to physical or chemical changes such as temperature change or change in pH the hydrogen bond gets disturbed causing the shape of the protein to

change the protein unfolds and loses its biological activity this is called denaturation of proteins interestingly the primary structure of a protein remains unaltered even during denaturation it means that the sequence of amino acids remains unchanged when we cook an egg the egg white gets coagulated this is because of the denaturation of proteins present in the egg white let's recap proteins are formed when a large number of amino acids bond together through peptide bonds depending upon the molecular shape of proteins they can be classified as fibrous proteins and globular proteins the structure of proteins can be

studied in four different levels that are primary secondary tertiary and quarternary structure of proteins if a native protein is subjected to physical or chemical changes it unfolds and loses its biological activity this is called the denaturation of protein