3.3
Synthèse de déshydratation
La synthèse par déshydratation est le processus chimique qui lie deux molécules ensemble de façon covalente en libérant une molécule d’eau. De nombreu…
Dehydration synthesis is a type of condensation reaction in which two monomers join by releasing a water molecule. This reaction can repeat many times, linking additional monomers to form large polymers.
For example, when a hydroxyl group of one glucose molecule reacts with a hydrogen atom of another glucose molecule, a water molecule is released, forming a glycosidic bond that links the sugars.
When many glucose molecules are linked together through repeated dehydration synthesis reactions, they form a polymer, called a polysaccharide.
Similarly, when the carboxyl group of one amino acid reacts with the amino group of another, water is released and a peptide bond forms.
Additional amino acids attach to the carboxyl end of the growing peptide chain, forming a polypeptide.
Dehydration synthesis can link similar or different polypeptides in various configurations, yielding diverse proteins with distinct structures and functions.
Similarly, glucose monomers can polymerize in various ways to form different polysaccharides, such as starch, cellulose, or glycogen.
View the full transcript and gain access to JoVE Core videos
Q1: What is dehydration synthesis and how does it work?
Dehydration synthesis is a condensation reaction where two monomers join together while releasing a water molecule. During this process, a hydroxyl group from one molecule combines with a hydrogen atom from another, and the remaining atoms form a covalent bond. This reaction can repeat many times to link additional monomers into large polymers.
Q2: How does dehydration synthesis form carbohydrates?
In carbohydrate synthesis, the hydroxyl group of one glucose molecule reacts with a hydrogen atom of another glucose molecule, releasing water and forming a glycosidic bond. When many glucose molecules undergo repeated dehydration synthesis, they form polysaccharides like starch, cellulose, and amylose. Different polymerization patterns create carbohydrates with distinct structures and functions.
Q3: What bond forms between amino acids during dehydration synthesis?
A peptide bond forms when the carboxyl group of one amino acid reacts with the amino group of another amino acid, releasing water. Additional amino acids attach to the carboxyl end of the growing peptide chain through repeated dehydration synthesis, forming a polypeptide. Different polypeptide configurations yield diverse proteins with distinct structures and functions.
Q4: How are lipids synthesized through dehydration synthesis?
Lipids such as triglycerides form when the three hydroxyl groups of a glycerol molecule react with the carboxyl groups of three fatty acids. This dehydration synthesis process releases three water molecules and forms ester bonds linking the glycerol to the fatty acids, creating a complete lipid molecule.
Q5: What role does dehydration synthesis play in nucleic acid formation?
Nucleic acids form through polymerization of nucleotide monomers via dehydration synthesis. Water molecules are removed as phosphodiester bonds form between consecutive nucleotides, linking them into long chains. This process creates DNA and RNA molecules essential for storing and expressing genetic information.
Q6: Why is dehydration synthesis important for building macromolecules?
Dehydration synthesis is the fundamental mechanism for creating all major macromolecules including carbohydrates, proteins, lipids, and nucleic acids. By linking monomers through covalent bonds while releasing water, this process builds complex molecules with diverse structures and physiological functions essential for life.
Q7: How does dehydration synthesis differ from hydrolysis?
Dehydration synthesis builds macromolecules by joining monomers and releasing water, while hydrolysis breaks macromolecules apart by adding water molecules. These are reverse reactions: dehydration synthesis creates polymers through condensation, whereas hydrolysis during biochemical reactions breaks them down into smaller components.