2.4 Condensation and Hydrolysis

The fundamental processes for building and breaking down biological macromolecules.

• Macromolecules (Polymers): Large, high molecular weight compounds made from many repeating smaller units.
• Micromolecules (Monomers): The individual repeating units that link together to form a polymer.
• The interconversion between monomers and polymers is managed by two primary reactions: condensation and hydrolysis.

Condensation (Dehydration Synthesis)

Condensation is an anabolic (building-up) reaction where monomers are joined together to form larger molecules (dimers or polymers).

• Process: A hydroxyl ($-OH$) group is removed from one monomer, and a hydrogen atom ($-H$) is removed from another.

• Byproduct: These removed atoms combine to form a molecule of water (${\mathrm{H}}_2\mathrm{O}$). This is why the process is also called dehydration synthesis (water is removed, a bond is synthesized).

• Bond Formation: The removal of the water molecule allows a covalent bond to form between the two monomers.

• Requirements: These reactions are not spontaneous; they require specific enzymes and the monomers must be in an activated, energy-rich state.

• Example 1 (Dimer Formation): Two Alpha-Glucose monomers join to form Maltose (a dimer), releasing one water molecule.

• Example 2 (Polymer Formation): Many Alpha-Glucose monomers are repeatedly joined to form a large polymer like Amylose (a type of starch).

• Calculation: The number of water molecules released equals one less than the number of monomers joined. For example, joining 20 monomers requires 19 bonds, releasing 19 water molecules ($n-1$ rule).

Hydrolysis

Hydrolysis is a catabolic (breaking-down) reaction that is essentially the reverse of condensation. It breaks down polymers or dimers into their constituent monomers.

• Process: A covalent bond between monomers is broken by the addition of a water molecule.

• Mechanism: The water molecule splits into a hydroxyl group ($-OH$) and a hydrogen atom ($-H$). The $-OH$ attaches to one monomer, and the $-H$ attaches to the other, restoring them to their original form.

• Biological Example: The digestion of food is a major example of hydrolysis. Enzymes like carbohydrases (break down carbohydrates), proteases (proteins), lipases (lipids), and nucleases (nucleic acids) catalyze these reactions.

• Example: The polymer Amylose is broken down into many Alpha-Glucose monomers by adding water molecules in the presence of the enzyme amylase.

Biological Significance of Hydrolysis in Everyday Life

Proteases (protein-digesting enzymes) are used in washing powders to remove blood stains from clothes. These enzymes hydrolyze the proteins in blood, breaking them into soluble peptides and amino acids that wash away.

Comparison Table