By the end of this lesson, you should be able to:
- Understand the synthesis of macromolecules
- Explain dehydration (or condensation) and hydrolysis reactions
Biological Macromolecules
Food provides the body with the nutrients it needs to survive. Many of these critical nutrients are biological macromolecules, or large molecules, necessary for life. Basically, these macromolecules (polymers) come from different combinations of smaller organic molecules (monomers). What specific types of biological macromolecules do living things require? How do the formations of these molecules occur? What functions do they serve? In this lesson and the next few, these questions will be explored.
Foods such as bread, fruit, and cheese are rich sources of biological macromolecules. Image Attribution: Modification of work by Bengt Nyman / OpenStax Biology
Biological Macromolecules
As you’ve learned, biological macromolecules are large molecules, necessary for life, that are built from smaller organic molecules. In general, there are four major classes of biological macromolecules (carbohydrates, lipids, proteins, and nucleic acids).
Each is an important cell component and performs a wide array of functions. Combined, these molecules make up the majority of a cell’s dry mass (recall that water makes up the majority of its complete mass). Biological macromolecules are organic, meaning they contain carbon. In addition, they may contain hydrogen, oxygen, nitrogen, and additional minor elements.
Dehydration Synthesis
Most macromolecules are made from single subunits, or building blocks, called monomers. The monomers combine with each other using covalent bonds to form larger molecules known as polymers. In doing so, monomers release water molecules as byproducts. This type of reaction is known as dehydration synthesis, which means “to put together while losing water.”
Most macromolecules are made from single subunits, or building blocks, called monomers. The monomers combine with each other using covalent bonds to form larger molecules known as polymers. In doing so, monomers release water molecules as byproducts. This type of reaction is known as dehydration synthesis, which means “to put together while losing water.” Image Attribution: OpenStax Biology
In a dehydration synthesis reaction (see image above), the hydrogen of one monomer combines with the hydroxyl group of another monomer, releasing a molecule of water. At the same time, the monomers share electrons and form covalent bonds. As additional monomers join, this chain of repeating monomers forms a polymer.
Different types of monomers can combine in many configurations, giving rise to a diverse group of macromolecules. In fact, even one kind of monomer can combine in a variety of ways to form several different polymers. For example, glucose monomers are the constituents of starch, glycogen, and cellulose.