Welcome back students. Let's see another biomolecule that is protein which is present in the living organisms. Now proteins are the particular sequences of amino acid that is the backbone of peptide chain or the protein. So mainly amino acids are called as a building blocks of proteins which make the long polypeptide chain which is called as protein. Now this is mainly the peptide bond which attaches these amino acids and the sequence of protein is formed. Now protein exists in a long chain of amino acids arranged in a particular sequence. Now the positional formation of amino acids in a protein is given by a primary structure of protein. A simple polypeptide chain which resembles the primary structure of proteins. The first amino acid is called as n terminal amino acid of this. This is the n terminal amino acid and the last amino acid of the protein chain is called as c terminal amino acid. Next comes the secondary structure of proteins which is also called as beta plated sheet. Now in this there is no interaction between every 4th amino acid by formation of hydrogen bonds and the polypeptide gets a helical shape that is of alpha helix as well as the beta plated sheet as you can be seeing here. Now individual polypeptides trans are observed. The polypeptide chains are arranged side by side as you can see here in this hydrogen bonds formed between these chains. These chains have hydrolygates in this manner. These proteins are sorry the polypeptide chains are arranged. Hydrogen bonds formed between the chains are group of extend above and below the sheet. The extend below above the sheet. Next the typical or their typical of fibrous proteins such as silk. So mainly this fibrous protein which is present in silk it is arranged in this manner. It has or you can say it has secondary structure of proteins. Next comes the triple helix. Three polypeptide chains woven together in the triple helix and glycine, proline, hydroxy proline and hydroxyl lysine are the examples of the triple helix. Edge bonding between OH groups gives a strong structure to the secondary structure and typical of like protein like collagen, connective tissue, skin, tendons and cartilage. All these are made up of this type of secondary structure. Now these amino acids or you can say the secondary structure of proteins also has alpha helix in which it has a helix shape like this. So in this there is no interaction between every four amino acid by formation of hydrogen bonds and the polypeptide gets a helical shape and example for this is the keratin. Next comes the tertiary structure. In this this is the specific overall shape of a protein and when the polypeptide becomes further stabilized by holding and coiling. The formation of ionic bonds or hydrophobic bonds or you can say the disulfide bridges. The protein is said to be tertiary in structure example for this can be amylase, pepsin or other enzyme. Now tertiary structure is absolutely necessary for many various biological activities. Cross linkages between the R groups is present. That means you can say the like disulfide bridges, ionic bonds, hydrogen bonds or hydrophobic bonds are also observed. So students in this session we have seen the protein structure in next session we will have a more detailed look on proteins. Thank you.