STPM Biology Biological Molecules Part 16 Amino Acids - Properties of Protein

1. Protein is amphoteric.

• Its structure has basic and acidic group.
• Amino group, NH2 is basic; while carboxyl group, COOH is acidic.

Structure of amino acid

2. Protein is an important buffer in biological systems.

• The amphoteric nature of protein allows it to function as a buffer.
• Amino groups of protein removes excess acids in the system.
• Carboxyl groups neutralize the excess bases in the system.

Protein as buffer in biological system

3. The colloidal nature of proteins allow it to exist as individual molecules in solution.

• Colloids are particles not soluble in water but remain suspended in the solution.
• Colloidal particles are usually 1nm to 100nm in diameter.
• Most globular proteins are soluble in water due to the small size of its molecule and existing polar groups such as -COOH.
• Globular protein with larger molecules will from colloidal suspensions in water.
• The colloidal nature of protein provides a larger surface are for biochemical reactions in cells.

Differences between solution, colloidal solution and suspensions

4. Protein denaturation.

• The change of structure and shape of the protein molecule due to the breaking down one or more bonds maintaining the structure of protein molecule is called protein denaturation.
• It can be caused by acids, bases, heat, pH and ultraviolet light.

Protein denaturation