A condensation reaction is a type of chemical reaction in which monomers (small molecules) join together to form polymers (large molecules or macromolecules).
During condensation, covalent bonds form between monomers, allowing them to join together into polymers. As these bonds form, water molecules are removed (or lost).
You might come across another name for condensation: dehydration synthesis or dehydration reaction.
Dehydration means to remove water (or loss of water - think what happens when you say you are dehydrated). Synthesis in biology refers to the creation of compounds (biological molecules).
In all likelihood, you have come across condensation in chemistry concerning the change of the physical states of matter - gas into liquid - and most commonly, the water cycle study. Yet condensation in biology doesn't mean that biological molecules turn from gases into liquids. Instead, it means the chemical bonds between molecules form with the elimination of water.
What is the general equation of a condensation reaction?
The general equation of condensation goes as follows:
A and B are stand in symbols for the molecules that are condensed, and AB stands for the compound produced from the condensation.
What is an example of a condensation reaction?
Let's use the condensation of galactose and glucose as an example.
Glucose and galactose are both simple sugars - monosaccharides. The result of their condensation reaction is lactose. Lactose is also a sugar, but it is a disaccharide, meaning that it consists of two monosaccharides: glucose and galactose. The two are linked together with a chemical bond called a glycosidic bond (a type of covalent bond).
The formula for lactose is , and galactose and glucose is .
The formula is the same, but the difference is in their molecular structures. Pay attention to the placement of the -OH on the 4th carbon atom in Figure 1.
Fig. 1 - The difference in molecular structures of galactose and glucose is in the position of the -OH group on the 4th carbon atom
If we remember the general equation of condensation, it goes as follows:
Now, let us swap A and B (groups of atoms) and AB (a compound) with galactose, glucose, and lactose formulas, respectively:
data-custom-editor="chemistry"
Notice that both molecules of galactose and glucose have six carbon atoms (C6), 12 hydrogen atoms (H12), and six oxygen atoms (O6).
As a new covalent bond forms, one of the sugars loses a hydrogen atom (H), and the other loses a hydroxyl group (OH). From these, a molecule of water is formed (H + OH = H2O).
Since a water molecule is one of the products, the resulting lactose has 22 hydrogen atoms (H22) instead of 24 and 11 oxygen atoms (O11) instead of 12.
The diagram of condensation of galactose and glucose would look like this:
Fig. 2 - The condensation reaction of galactose and glucose
The same thing happens during other condensation reactions: monomers join to form polymers, and covalent bonds form.
Therefore, we can conclude that:
A condensation reaction of monomers monosaccharides forms covalent glycosidic bonds between these monomers. In our example above, disaccharide forms, meaning two monosaccharides join together. If multiple monosaccharides join together, a polymer polysaccharide (or complex carbohydrate) forms.
The condensation reaction of monomers that are amino acids results in polymers called polypeptides (or proteins). The covalent bond formed between amino acids is a peptide bond.
The condensation reaction of monomers nucleotides forms a covalent bond called a phosphodiester bond between these monomers. The products are polymers called polynucleotides (or nucleic acids).
Although lipids are not polymers (fatty acids and glycerol are not their monomers), they form during condensation.
Note that a condensation reaction is the opposite of a hydrolysis reaction. During hydrolysis, polymers are not made as in condensation but are broken down. Also, water is not removed but added in a hydrolysis reaction.
What is the purpose of a condensation reaction?
The purpose of a condensation reaction is the creation of polymers (large molecules or macromolecules), such as carbohydrates, proteins, lipids, and nucleic acids, all of which are essential in living organisms.
They are all equally important:
Condensation of glucose molecules allows for creating complex carbohydrates, for instance, glycogen, which is used for energy storage. Another example is the formation of cellulose, a carbohydrate that is the main structural component of cell walls.
The condensation of nucleotides forms nucleic acids: DNA and RNA. They are crucial for all living matter as they carry genetic material.
Lipids are essential energy storage molecules, building blocks of cell membranes and providers of insulation and protection, and they form in the condensation reaction between fatty acids and glycerol.
Without condensation, none of these essential functions would be possible.
Condensation Reaction - Key takeaways
Condensation is a chemical reaction during which monomers (small molecules) join to form polymers (large molecules or macromolecules).
During condensation, covalent bonds form between monomers, which allow monomers to join together into polymers. Water is released or lost during condensation.
Monosaccharides galactose and glucose covalently bond to form lactose, a disaccharide. The bond is called a glycosidic bond.
Condensation of all monomers results in the formation of polymers: monosaccharides covalently bond with glycosidic bonds to form polymers polysaccharides; amino acids covalently bond with peptide bonds to form polymers polypeptides; nucleotides covalently bond with phosphodiester bonds to form polymers polynucleotides.
The condensation reaction of fatty acids and glycerol (not monomers!) results in the formation of lipids. The covalent bond here is called the ester bond.
The purpose of a condensation reaction is the creation of polymers that are essential in living organisms.
Explanations 
Exams 
Magazine 
