Chapter 6: Introduction to Organic Chemistry

6.3. Common Biochemical Reactions

Learning Objectives

By the end of this section, you will be able to:

  • Describe and contrast two common biochemical reactions, dehydration synthesis and hydrolysis.

Dehydration Synthesis (Condensation)

This is a process of anabolism. Dehydration uses monomers (single subunits or building blocks) to build a larger molecule by joining the molecules in covalent bonds and releasing water as a product (hence, condensation). In order to join monomers together in a covalent bond, the hydroxyl (-OH) of one monomer and the Hydrogen (H) of another are removed, releasing H-OH, water. This frees up valence electrons for bond formation between the monomers. Dehydration synthesis is illustrated below (Figure 6.3.1.) using the example of building a carbohydrate macromolecule from its monomers, glucose. But note that dehydration reactions are common in all biomolecule families.

Shown is the reaction of two glucose monomers to form maltose. When maltose is formed, a water molecules is released. The components of the linkage are upper case O upper case H from one glucose molecule combining with one upper case H from the second glucose molecule.
Figure 6.3.1: Dehydration synthesis.

Hydrolysis

This is a process of catabolism. Hydrolysis means to ‘split’ water (hydro- water, lysis -break). The reaction uses water to break down larger molecules into either smaller subunits or monomers. Hydrolysis is the process used by our digestive system to break down ingested nutrient macromolecules to their monomers, the only form that can be used by cells. 

We will again use a carbohydrate as the process example (Figure 6.3.2.). The chemical reactions involves inserting a water molecule across the covalent bond between the macromolecule’s monomers. Upon release of the monomers, one has gained a hydrogen atom (H) and the other gains a hydroxyl group (-OH) from a split water molecule.

Shown is the breakdown of maltose to form two glucose monomers. Water is a reactant. The water molecule, upper case H subscript 2 baseline upper case O, breaks apart, with upper O upper H obtained by one of the glucose molecules, and upper H obtained by the second glucose molecule.
Figure 6.3.2: Hydrolysis reaction. Covalent bonds joining the macromolecules are broken by the use of a water molecule.

Both dehydration synthesis and hydrolysis reactions are catalyzed, or “sped up,” by specific proteins called enzymes (discussed in the next chapter).

Glossary

anabolism: larger molecule is built from the combination of smaller molecules

catabolism: >larger molecules are broken down into smaller molecules

dehydration synthesis: the combination of smaller molecules with the removal of water

hydrolysis: the breakdown of larger molecule with the use of water

metabolism: chemical reactions occurring in cells

License and attributions:

    • Biology, Second edition, 2018, Clark, M.A. et al. License: CC BY 4.0. Located at https://openstax.org/books/biology-2e/pages/2-3-carbon
    • Biology for AP Courses, 2018, Zedalis, J. et al. License: CC BY 4.0. Located at https://openstax.org/books/biology-ap-courses/pages/3-1-synthesis-of-biological-macromolecules

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BIO130: Introduction to Physiology Copyright © 2024 by Dinor Dhanabala; Sandra Fraley; and Gordon Lake is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

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