Dehydration Synthesis

Introduction

Dehydration synthesis describes the formation of larger molecules from the smaller reactant molecules along with the loss of a water molecule. A dehydration reaction is a subpart of a condensation reaction where water is the most common by-product. In the process of Dehydration synthesis, two smaller molecules are joined chemically while removing elements from both the reactant molecules and forming a new covalent bond. Dehydration means the loss of water and synthesis means the formation of a new molecule. In biological systems, dehydration synthesis refers to the formation of biological polymers by the addition of monomers which is again accompanied by the elimination of water molecules. For example, amino acids as monomers combine to form the peptide as a polymer. Here a new covalent bond, a peptide bond is formed which is present between two amino acid molecules. Dehydration Synthesis generates the Building Blocks of life. Several important compounds are formed by dehydration synthesis, such as carbohydrates, proteins, DNA, and RNA.

What do you mean by Dehydration Reaction?

Dehydration means loss of water. A dehydration reaction is a reaction where two reactant molecules combine to produce an unsaturated molecule along with a water molecule as a by-product. In this process the hydrogen ion of one molecule joins with the hydroxide ion of the other molecule. A dehydration reaction is just the reverse of a hydration reaction where water molecules are added to the reaction. Some examples of Dehydration reactions are-

• The formation of symmetric ethers from alcohol condensation is a common example of a dehydration reaction.

$$\mathrm{2C_{2}H_{5}OH\:\leftrightarrows\:C_{2}H_{5}OC_{2}H_{5}\:+\:H_{2}O}$$

• Esterification is a special type of dehydration reaction in which carboxylic acid and alcohol combine to form an ester and a water molecule is formed as a by- product.

$$\mathrm{R_{1}COOH\:+\:R_{2}OH\:\rightarrow\:R_{1}COOR_{2}\:+\:H_{2}O}$$

Dehydration Synthesis of 2 Amino Acids

An amine group and a carboxylic acid serve as functional groups in amino acids. On the same carbon atom, these two groups can be found. An amide bond is created when the amine group on one amino acid combines with the acid group on another amino acid. In a dehydration synthesis involving two amino acids where the functional groups present are 𝑁𝐻2 and 𝐶𝑂𝑂𝐻, a polymer peptide is formed from Monomer amino acids.

One unit of Amino acid

One of the amino acids releases an 𝐻+ion. This released 𝐻+ ion then combines with the 𝑂𝐻− ion present in another amino acid. In this way, two monomer amino acids form a covalent bond in between and a dipeptide is formed. All polypeptide has an N terminal, where a free amino group is present, and a C terminal, where a free carboxyl group is present. Dehydration synthesis can be reversible also. Hydrolysis is the most common example of a reversible reaction to dehydration synthesis.

Dehydration synthesis of Amino acids to form a polymer

Protein Dehydration Synthesis

The process of creating larger molecules from smaller monomers is known as dehydration synthesis. The dehydration synthesis procedure is used to produce big biological molecules like proteins, carbohydrates, and nucleic acids. Although the position and stereochemistry of the covalent connection connecting the monomers do not alter from one molecule to the next (proteins contain 21 distinct amino acid monomers), the sequences in which they are assembled do. Each protein has a unique sequence, making each one a unique molecule with unique features.

The amine group of an amino acid can react with lots of acid groups to form a peptide bond, which is covalent. the newly formed acid i.e., the polymer formed from monomer, still contains one free amine group along with one free carboxylic acid. Hence the reaction can proceed further with more numbers of amino acids. Amino acids are linked together in a form of a linear chain. The number of amino acids combined, and the sequence of combination determines the protein’s shape, size, and function.

How does dehydration synthesis contribute to the formation of ATP?

Adenosine triphosphate or ATP is a small and simple molecule. It is the main energy currency of cells. A phosphate group is added to ADP with the help of an enzyme called ATP synthase to form ATP. This process is called oxidative phosphorylation. Adenosine triphosphate is a combination of the nitrogenous base adenine, three phosphate groups and the five-carbon sugar ribose. ADP unit combines with a phosphate unit to form ATP. The energy derived from ATP hydrolysis in this process is used in Sodium-potassium pumps to pump sodium and potassium ions across the cell membrane. In the reaction of dehydration synthesis of ADP to form ATP water molecule is released. The three phosphate groups are labelled as alpha, beta, and gamma to understand the closest one and the furthest one from the ribose sugar respectively. All these chemical groups together form an energy powerhouse. ADP is combined with a phosphate to form ATP in the following reaction −

$$\mathrm{ADP\:+\:P_{1}\:+\:free\:energy\:\leftrightarrows\:ATP\:+\:H_{2}O}$$

Dehydration synthesis for formation of ATP or hydrolysis of ATP to form ADP

Muessig, ADP ATP cycle, CC BY-SA 3.0

How does dehydration synthesis lead to the formation of carbohydrate polymers?

Carbohydrates are polymers that are made up of sugar molecules, which include glucose, fructose, and arabinose. These sugar molecules act like a monomer here. When this monomer combines, it forms dimers such as sucrose, lactose, cellulose, starch, etc. The monomer sugar molecules combine via the formation of a glycosidic bond. This glycosidic bond is formed by the dehydration synthesis process. An 𝑂𝐻 group of one sugar molecule and another 𝑂𝐻 groups from another sugar molecule combine to form a bond between the two molecules. A bridge of an oxygen atom is formed between the two molecules with the release of a water molecule.

Formation of carbohydrate polymer

How are triglycerides formed by dehydration synthesis?

Triglycerides (Lipids) also called fats, are formed when three fatty acid molecules attach to a glycerol molecule. The formation of triglycerides is an esterification reaction which is again a dehydration synthesis reaction. The alcohol groups present on the glycerol molecule combine with the acidic group on fatty to form an ester bond with the release of water. The fatty acids contain carboxylic acids where one carboxyl group is present at the end of a linear hydrocarbon containing at least four carbon atoms. Various enzymes catalyse the dehydration synthesis of triglycerides. Diacylglycerol acyltransferase 1 (DGAT1) is one of them. This enzymatic reaction is present in mammalian triglyceride synthesis.

Formation of triglycerides by dehydration synthesis

OpenStax College 220 Triglycerides-01, CC BY 3.0

Conclusion

A dehydration reaction is a subunit of a condensation reaction. Monomers combine to form polymers along with loss of water molecules. Dehydration synthesis refers to the formation of biological polymers which is again accompanied by the elimination of water molecules. This process is also used in the creation of synthetic polymers such as polyethylene, terephthalate (PET), etc. In biological systems, dehydration synthesis reactions are very special and involve the formation of ATP, carbohydrate, protein, etc.

FAQs

1. What happens if dehydration synthesis does not occur?

Dehydration synthesis is very important in biological systems. Life would have been difficult without a dehydration reaction when no protein, no ATP, no carbohydrate, and many more important biological molecules will not be present.

2. What does dehydration synthesis require?

Dehydration synthesis reactions form large and complex molecules and generally require energy. Hydrolysis reactions are just the opposite, here molecules break down and generally release energy.

3. Is dehydration synthesis exothermic or endothermic?

In all Dehydration synthesis reactions small monomers combine to form large polymer molecules which generally require energy. Hence Dehydration synthesis is endothermic.

4. What molecule is lost in the dehydration reaction?

A dehydration reaction is just the opposite of a hydration reaction. It is a chemical reaction that involves the loss of water. Dehydration reactions are very common reactions in biological systems where the polymer is formed along with the release of water into the system.

5. What is the purpose of dehydration?

We have so many purposes for dehydration reactions in our life. This dehydration is a very important process by which many types of food can be preserved. This preservation of food for indefinite periods takes place by extracting the moisture from food that inhibits the growth of microorganisms.