Question

One of the following sets will get coagulated on heating
A. Egg white and serum albumin
B. Histones and protamines of corn
C. Gliadin of wheat
D. All of the above

Answer 1

Hint: Proteins form secondary, tertiary, and quaternary structures from their primary structures based on the composition of the amino acids present and possess a functional form. Coagulation is the conversion of protein from liquid to solid form.

Complete answer:
The heat can cause denaturation of proteins by breaking the hydrogen and non-polar hydrophobic interactions. The secondary, tertiary, or quaternary structures are denatured but not the primary structure since it is not strong enough to break the peptide bonds so the amino acid sequence remains the same even after denaturation. Heat causes the coagulation of the proteins where the protein when denatured becomes solid in nature as it loses many hydrogen bonds. It is irreversible and occurs mainly by heating the proteins between 38°C to 71°C.

> Option A:
Egg white contains different proteins among which ovalbumin and ovotransferrin are in the highest concentration whereas egg yolk mainly has different lipids. So on heating, the egg white and proteins present in the serum-like, serum albumin denatures and forms coagulation and thus shrink in size. This is the method used for cooking eggs. The egg white can coagulate at temperatures between 60°C to 65°C.

> Option B:
Histones are the proteins used in the formation of nucleosome units as their positive charge allows negatively charged DNA to wound around. The heating is not strong enough to break the peptide bond in histone protein. Heat can only break the hydrogen bond between DNA and histone proteins.

> Option C:
Gliadin is the water-insoluble protein in wheat. On heating, there is only heat-induced malformation and no coagulation is seen.

Hence, the correct answer is option (A).

Note: Heating is one of the procedures used for sterilization as the proteins in the bacteria denature and coagulate and break down the cell membrane causing the death of bacteria. It is also used in cooking procedures.