Differentiate between the tertiary and quaternary structure of protein.

Hint: Protein is a chain of many amino acids linked together by covalent bonds. They form long linear chains called polypeptides which when folds form a three-dimensional structure. The R-group in proteins includes hydrogen bonding, dipole-dipole interactions, ionic bonding, and non-covalent bonds.

Complete answer:
The overall peptide’s three-dimensional shape is called the tertiary structure of the protein. The interactions between the R groups of the amino acids are the primary reason for the tertiary structure of a protein.
> The R-groups of like charges repel each other and that of opposite charges form ionic bonds. The polar R groups can form hydrogen bonds and dipole-dipole interactions.
> Tertiary structures also have hydrophobic interactions. In this, the R group clusters inside the protein leaving the hydrophilic amino acid outside. The hydrophilic amino acid is then surrounded by water molecules.
> The disulphide bond is a special type of covalent bond which contributes to the tertiary structure. They are sulphur-containing chains and have strong bonds.
Some proteins have subunits that are made up of multiple polypeptide chains. The quaternary structure of the protein is formed when these subunits come together.
> An example of a protein with a quaternary structure is hemoglobin. Hemoglobin is made up of four subunits, two each of alpha and beta types.
> The quaternary structure gives rise to the complex arrangement in the protein.
> Another example is DNA which consists of ten subunits.

Note:
The folds in the protein are stabilized by different covalent bonds. Proteins although being macromolecules are very small to be seen even under a microscope. The interactions that hold the tertiary structure also hold the subunits in the quaternary structure.