The amide functional group has a carbon atom double-bonded to an oxygen atom and single-bonded to a nitrogen atom. An amide is created by a dehydration synthesis with an organic acid and an amine. Notice that the amide functional group looks like an ester with a nitrogen in place of an oxygen. (Compare Figure with Figure .) The dehydration synthesis of an amide is shown in Figure .
An ester is formed by dehydration synthesis with an organic acid and an alcohol. An alcohol and an organic acid combine to form an ester and water. An example of an ester is shown in Figure .
The chemical reactions that form covalent bonds between monomers are collectively called reactions. In this type of reaction, a water molecule is released as a product, effectively dehydrating the reactants as a larger biomolecule is synthesized. Dehydration synthesis is also called a condensation reaction due to the removal of water (condensation = water “condenses” out). In each of the four macromolecule groups, the specific chemical bonds formed by dehydration synthesis involve unique atom pairs and three-dimensional positions, affecting the structure and function of each biomolecule differently.
The opposite chemical reaction occurs when polymers are separated into individual monomers. reactions incorporate the atoms from a water molecule into each monomer as the chemical bond between the monomers is broken (hydrolysis = water “loosens” the bond). In hydrolysis reactions, water participates in the chemical reaction as a reactant. A cell’s collective metabolism results from the balance between these reciprocal reactions. Cells use dehydration synthesis reactions to build the functional biomolecules that support life. When biomolecules are damaged or no longer needed, cells use hydrolysis reactions to degrade the polymers and frequently recycle the monomers to form new biomolecules.
Additionally, many macromolecules are involved in regulating and promoting the synthesis and breakdown of other macromolecules. Carbohydrates and lipids store energy needed to drive synthesis reactions. Nucleic acids store and transmit information that directs which macromolecules to synthesize, while protein and nucleic acid enzymes catalyze chemical reactions in both synthesis and degradation of macromolecules. The sum of all chemical reactions synthesizing and breaking down in living organisms is collectively referred to as an organism’s .
The monomers of organic compounds join together by a chemical reaction know as dehydration synthesis to make polymers. The reverse reaction of breaking up polymers is accomplished by another chemical reaction known as hydrolysis. This interactive animation illustrates both reactions.
An amino acid is a carbon atom bonded to an amine, a carboxyl group and some third group that we sometimes indicate as . In Figure two amino acids are distinguished by un-named groups and . Through dehydration synthesis an amide bond is formed. In the context of amino acids this bond is called a peptide bond, and two linked amino acids is called a dipeptide.