The Science Behind Dehydration Synthesis and Hydrolysis

Dehydration Synthesis

Dehydration Synthesis: Despite being very diverse, life can still be broken down into its 4 major building blocks: carbohydrates, proteins, lipids, and nucleic acids.

Being a constituent of living organisms, a more general name for this group of organic compounds is biomolecules. These biomolecules are needed for survival: carbohydrates and lipids for energy source, proteins for structural support, and nucleic acids for carrying genetic information.

Water is essential in numerous cellular processes. In fact, in the presence of water, dehydration synthesis and hydrolysis are the biochemical processes that are used to either build or break down the said biological molecules.

Let’s take a look and explore what actually happen in these reactions.

What is Dehydration Synthesis?

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.

Dehydration Synthesis and Hydrolysis
Dehydration Synthesis and Hydrolysis (Source: Wikimedia)

Types of Dehydration Synthesis

In biological organisms, various types of dehydration synthesis occur. Such are classified based on the following:

1. Based on the nature of reactants

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.

2. Based on the nature of the catalyst

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.

3. Based on the product formed

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.

What is Hydrolysis?

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.

Types of Hydrolysis

Various types of hydrolysis occur in living organisms. The three types[4] are listed below:

1. Salt Hydrolysis

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.

2. Acid Hydrolysis

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.

3. Base Hydrolysis

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.

Reactions of Dehydration Synthesis and Hydrolysis

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:

Type of Organic Compound Type of Bond Involved Dehydration Synthesis Hydrolysis
Carbohydrates Glycosidic bond Two or more monosaccharides combined = Disaccharide/Polysaccharide + H2O Disaccharide/Polysaccharide + H2O = Monosaccharide units
Proteins Peptide bond Two or more amino acids =Dipeptide/Protein + H2O Dipeptide/Protein + H2O = Two or more amino acids
Lipids Ester bond 3 Fatty acids + Glycerol = Lipid molecule Lipid molecule + 3 H2O = 3 Fatty acids + Glycerol
Nucleic acids Phosphodiester bond 10 nucleotides = Nucleic acid + H2O Nucleic acid + H2O = 10 nucleotides

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

Roles of Dehydration Synthesis in Biological Systems & Examples

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.

Roles of Hydrolysis in Biological Systems & Examples

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.

From being a mere thirst quencher to a facilitator of photosynthesis to becoming a builder or breaker of molecular compounds, we have seen that at molecular level, water is undeniably essential for living organisms. What do you think are other abilities and uses of this compound?

Cite this article as: "The Science Behind Dehydration Synthesis and Hydrolysis," in Bio Explorer, February 22, 2017,


  • [1]“Dehydration Synthesis: Definition, Reaction & Examples – Video & Lesson Transcript |”. Accessed February 20, 2017. Link.
  • [2]“Hydrolysis and Dehydration Synthesis: How we become what we eat”. Accessed February 20, 2017. PDF.
  • [3]“Online Introduction to Biology – Chemistry – Important Molecules in Living Systems”. Accessed February 20, 2017. Link.
  • [4]“Hydrolysis – Chemistry LibreTexts”. Accessed February 20, 2017. Link.
The Science Behind Dehydration Synthesis and Hydrolysis
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