The Science Behind Dehydration Synthesis and Hydrolysis

Also known as condensation reaction, dehydration synthesis^[1] is the process of combining small molecules (called monomers) in order to produce larger units (called polymers), following the removal of water (H₂O):

• In this process, a hydrogen ion (H+) from one component and a hydroxide ion (OH-) from the succeeding component are removed. The hydrogen ion and hydroxide then combine to form water, hence, the components appear to “lose water” or “dehydrate“.
• Dehydration synthesis is also called as “condensation reaction” because both are characterized by the condensation and formation of water from the large molecule.
• Examples of dehydration synthesis reactions are the conversion of monosaccharides to complex sugars, production of proteins from amino acids, conversion of fatty acids to complex fats, and the formation of nucleic acids from nucleotides.

The diagram below illustrates how dehydration synthesis generally occur in polymers.

For instance, this criterion is due to the fact that biomolecules and their building blocks are made of chemical elements and functional groups that are combined together. Basically, this category simply classifies them whether they are of the amine group, carboxyl group, and others.

In living organisms, chemical parameters like pH, temperature, and salinity are variable. Hence, biological catalysts, or enzymes that speed up chemical reactions are needed. Along with that, the type of dehydration synthesis is named after the catalyst that drive the reaction.

As mentioned earlier, dehydration synthesis can produce a wide variety of polymer products. Therefore, these types of reactions are grouped whether they form complex carbohydrates from simple sugars, create fatty acids from Acetyl-CoA, and others.

Relative to the process of dehydration synthesis, hydrolysis^[2] is merely the reverse. Using water molecules complex molecules are broken down into smaller units.

• Large molecules are broken down by breaking the bond between water molecules. In this process, a hydrogen ion (H+) is added to one component and a hydroxide ion (OH-) is added to another one.
• Since water is split, it is termed as “hydrolysis” which literally means “water separation“^[3].
• Examples of hydrolytic reactions are the breaking down of complex sugars, proteins, complex fats, and nucleic acids into monosaccharides, amino acids, fatty acids, and nucleotides.

This occurs when a salt when a salt is dissolved in water. The water then is converted to hydrogen ions (H+) and hydroxyl ions (OH-) as salt dissociates into cations and anions.

According to the Bronsted-Lowry theory, water can act as either an acid or a base. If the water molecule donates proton (H+), water is said to act as an acid.

In relation to what was mentioned above, the water molecule can act as a base and hydrolyze molecules. If the molecule accepts the proton (H+) from water, the molecule is said to act as a base.

As mentioned earlier, dehydration hydrolysis work the same way in the four major macromolecules. The table below will give you more simplified view of their reactions:

Should you need more illustrations, you may check this YouTube video below:

In most autotrophic organisms utilize dehydration synthesis in order to form long chains of small molecules. For instance, this process used for storing excess glucose by converting it to glycogen (storage form of carbohydrates in animals) or starch (storage form of carbohydrates) in plants.

• Another common example of dehydration synthesis in plants is the production of maltose (malt sugar) from the fusion of two glucose units resulting from the freeing of water molecule. Other polymers of carbohydrates are also formed this way.

On the other hand, in heterotrophic (unable to photosynthesize) organisms, the digestion of food into smaller substances is important to absorb the nutrients and convert them to a more usable form of energy. When the body needs energy to biosynthesize, this energy in the form of ATP undergoes hydrolysis and after which can now be utilized.

• In animals, digestion is one of the most common example of hydrolysis. Food is broken down (hydrolyzed) into small units by different enzymes present in the digestive tract. Such pave the way for the easier absorption of nutrients in the small intestine.
• Other examples include the hydrolysis of fat as this helps in the prevention of them clotting in different parts of the body.