CHAPTER 19: Unit 2. Types of Proteins: Primary Structure

Proteins are made of the condensation reactions of 50 amino acids or more connected via a peptide bond.

The dipeptide is made of two amino acids and the tripeptide is made of three amino acids and tetrapeptide is made of four amino acids etc.

There are four types of protein structures:

Reference: https://www.thoughtco.com/protein-structure-373563

The videos below illustrate these types of protein structures:

The detailed structure of primary protein is given in the figure below:

Reference: https://socratic.org/questions/how-would-you-describe-the-primary-structure-of-a-protein

An example of the primary structure is a human insulin which is made of 2 chains A and B connected through S – S bridge (or disulfide bond) at specified carbon atoms.The S – S bridge (or disulfide bond) is also found in the A chain C – terminus.  Chain A is made of 21 carbon atoms and Chain B is made of 30 carbon atoms.

References:https://www.jbclinpharm.org/articles/review-of-insulin-and-its-analogues-in-diabetes-mellitus.html

The function of insulin is to regulate the amount of glucose in the blood stream. The insulin is produced in the pancreases.When the S-S bond is bridging both chains, the insulin is said to be biologically inactive and called C peptide and it is stored in the granules in the pancreases. When insulin is needed (for example to lower amount of sugar in blood steam) then the S – S bond or bridge between the two chain is broken and the chains are free, and the insulin is said to be biologically active.