How Macromolecules are built

Given the rich diversity of life, we might expect organisms to have an enormous variety of molecules. However the significant large molecules of all living things can be classified into four categories: carbohydrates, lipids, proteins, and nucleic acids. Only three of these categories- carbohydrates, proteins, and nucleic acids- are huge on a molecular scale and are called macromolecules. In this post, we will consider how macromolecules are built. Then we will examine the structure and function of these four large biological molecules in the next posts.

Macromolecules are polymers, built from monomers

The macromolecules (carbohydrates, proteins, and nucleic acids) are chain-like molecules called polymers, which are long molecules that contain molecules that are similar or identical linked by covalent bonds. Monomers are these building molecules that are similar or identical and serve as the building blocks of the molecules.

The synthesis and breakdown of polymers

The chemical procedure of how cells make and break down polymers are basically the same throughout every class of polymer. Polymers are synthesized by a reaction known as a condensation reaction, specifically dehydration reaction. Dehydration Reactions link monomers with a covalent bond through the loss of a water molecule. The dehydration reaction is facilitated by enzymes, specialized macromolecules (mostly proteins) that speed up chemical reactions.

Image result for dehydration reaction in the synthesis of a polymer
In the picture above, this highlights a dehydration reaction. One monomer provides a hydroxyl group and the other monomer provides a hydrogen to create a water molecule and the monomers are linked covalently.

Polymers are broken by hydrolysis (literally meaning to break using water), a process that is basically the opposite of the dehydration reaction. The bonds between the two monomers are broken by the addition of a water molecule.

Image result for hydrolysis reaction
A diagram illustrating a hydrolysis reaction. A hydrogen from the water is linked to one monomer and a hydroxyl group is linked to the other monomer. 

The Diversity of Polymers

Small molecules common to all organisms are ordered into unique combinations to make unique polymers. Despite great diversity of polymers, members of each of the 4 major classes of large molecules are similar in structure and function. 

In the next post, we will discuss the structure and function of carbohydrates.

-Tahmid Islam

Co-Founder and Editor of STEMTalksNC

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