What is the structure of a protein?

Structure of the protein is easier to understand if we start from the beginning and gradually build up our knowledge. Firstly, proteins are made of amino acids. Each amino acid is made of a central carbon atom , carboxyl group (-COOH), amine group (-NH₂), hydrogen atom and R group ( this one varies depending on the amino acid). Amino acids join together via peptide bond (p - for protein, p - for peptide) to form a polypeptide chain.We can describe the structure of a protein using 4 stages:Primary structure - this is the order of amino acids in the polypeptide chain. We can imagine each amino acid is a bead placed on the string to visualise this concept.Secondary structure - this is the shape polypeptide chain folds into. Two most common shapes are alpha - helix and beta - pleated sheet. Useful to know that it is determined by the hydrogen bonds.Tertiary structure - this is the three dimensional structure of a protein. It is determined by the interactions between the R - groups of different amino acids e.g. disulfide bridges or hydophilic-hydrophobic interactions.Quaternary structure - this is the arrangement of polypeptide chains and applies only to the proteins which are made of more than 1 chain.