Hydrolysis Reaction

Hydrolysis is a chemical reaction during which polymers (large molecules) break down into monomers (small molecules).

During hydrolysis, covalent bonds between monomers break, which allows for the breaking down of polymers. Bonds are broken down using water. Hydro literally means 'water', and - lysis stands for 'to unbind'.

What is the general equation of a hydrolysis reaction?

The general equation of hydrolysis is the general equation for condensation, but reversed:

$\mathrm{AB}+{\mathrm{H}}_2\mathrm{O}\to \mathrm{AH}+\mathrm{BOH}$

AB stands for a compound, while A and B stand for atoms or groups of atoms.

What is an example of a hydrolysis reaction?

Lactose is a simple carbohydrate - a disaccharide composed of two monosaccharides: galactose and glucose. Lactose is formed when glucose and galactose bond with glycosidic bonds. Here, we will again take lactose as an example - although we are now splitting it instead of condensing it!

If we swap the AB, and the A and B from the general equation above with the lactose, galactose, and glucose formulas, we get the following:

${\mathrm{C}}_{12}{\mathrm{H}}_{22}{\mathrm{O}}_{11}+{\mathrm{H}}_2\mathrm{O}\to {\mathrm{C}}_6{\mathrm{H}}_{12}{\mathrm{O}}_6+{\mathrm{C}}_6{\mathrm{H}}_{12}{\mathrm{O}}_6$

After the breakdown of lactose, both galactose and glucose each have six carbon atoms (C6), 12 hydrogen atoms (H12), and six oxygen atoms (O6).

Notice that lactose has 22 hydrogen atoms and 11 oxygen atoms, so how do both sugars end up with H12 and O6?

When the water molecule splits to break the bond between two monomers, both galactose and glucose gain one hydrogen atom (which then makes it 12 for each molecule), and one of them gets the remaining oxygen atom, leaving them both with 6 in total.

Therefore, the water molecule is split between both resulting sugars , with one receiving the hydrogen atom (H) and the other receiving the hydroxyl group (OH).

The diagram of hydrolysis of lactose would look like this:

Fig. 1 - The hydrolysis reaction of lactose

The hydrolysis reaction is the same for all polymers, as well as lipids. Similarly, condensation is the same for all monomers, along with non-monomers that are fatty acids and glycerol.

Therefore, you can conclude that:

• The hydrolysis reaction of polymers polysaccharides breaks them down into monomers: monosaccharides. Water is added, and covalent glycosidic bonds between monosaccharides are broken.

• The hydrolysis reaction of polymers polypeptides breaks them down into monomers that are amino acids . Water is added, and covalent peptide bonds between amino acids are broken.

• The hydrolysis reaction of polymers polynucleotides breaks them down into monomers: nucleotides. Water is added, and covalent phosphodiester bonds between nucleotides are broken.

So, for the breaking down of lipids:

During the hydrolysis reaction of lipids, they are broken down into their constituents, fatty acids, and glycerol. Water is added, and covalent ester bonds between fatty acids and glycerol are broken.

What is the purpose of hydrolysis reaction?

Hydrolysis is crucial for the normal functioning of cells. By allowing large molecules to break down, hydrolysis ensures the smaller molecules are formed. These are absorbed by cells more easily. This way, cells get their energy for cellular activities.

One of the most straightforward examples would be the food we eat. Macromolecules such as proteins in meat and cheese and lipids in fats are first broken down in the digestive tract before any energy reaches the cells. Various enzymes (proteins) help hydrolysis reactions.

Without hydrolysis, cells would not be able to function properly. And if you remember that cells make every part of our bodies, it means that all living organisms rely on both condensation and hydrolysis to store and release much-needed energy.