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DEHYDRATION SYNTHESIS: DESPITE BEING VERY DIVERSE, LIFE CAN BE BROKEN DOWN INTO ITS FOUR MAJOR BUILDING BLOCKS: CARBOHYDRATES, PROTEINS, LIPIDS AND NUCLEIC ACIDS.
Being a constituent ofliving 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 process- es. 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 happens 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, H²O, 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 monosaccha -rides 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
(a) Dehydration synthesis: Monomers are joined by removal of OH from one monomer and removal of H from the other at the site of bond formation. (Monomer 1)— OH + HO —(Monomer 2)
⤴H₂O→
Monomers linked by covalent bond
(b) Hydrolysis: Monomers are released by the addition of a water molecule, adding OH to one monomer and H to the other.
Monomers linked by covalent bond
⤷H₂O→
(Monomer 1) — OH
+ HO — (Monomer 2)
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 biomole- cules 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 mole- cules 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 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: here
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 under- goes 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 water is undeniably essential for living organisms at the molecular level. What do you think are other abilities and uses of this compound?
●Type of Organic Compound¹ Type of Bond Involved² Dehydration Synthesis³ Hydrolysis⁴
●¹Carbohydrates¹Glycosidic bond²Two or more monosacchar- ides combined = Disacchar- ide/ Polysaccharide + H2O³Disaccharide/Polysacchari- de+H2O = Monosaccharide units⁴
●Proteins¹ Peptide bond² Two or more amino acids =Dipeptide/Protein + H2O³ Dipeptide/Protein + H2O = Two or more amino acids⁴
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