Carbohydrates are a broad category of organic compounds found in many foods, serving as a primary source of energy for the body. They are one of the three main macronutrients, alongside proteins and fats, that humans consume. Like other large biological molecules, carbohydrates are constructed from smaller, repeating units.
Introducing Monomers: The Basic Building Blocks
In biology, a monomer is a single, fundamental unit that can join with other similar units to build larger, more complex structures. These larger molecules, formed from many linked monomers, are known as polymers. For carbohydrates, these basic building blocks are simple sugar molecules, specifically called monosaccharides. They represent the smallest and most fundamental form of carbohydrates. Monosaccharides are the simplest sugars, and they cannot be broken down into smaller sugar units through digestion.
The Key Monomers of Carbohydrates
The three most common and biologically significant carbohydrate monomers are glucose, fructose, and galactose. Glucose is the most prevalent monosaccharide found in nature and serves as the main type of sugar in the bloodstream. It is the primary energy source for the body’s cells and the brain. Plants produce glucose through photosynthesis, storing it in linked chains like starch, and it is also found in foods such as honey and dried fruits.
Fructose, often referred to as “fruit sugar,” is another simple sugar naturally present in many fruits, vegetables, and honey. It is known for being the sweetest naturally occurring carbohydrate. Galactose is a monosaccharide that is not typically found in large free quantities in nature, but it is a component of lactose, the sugar found in milk. While these three monosaccharides have the same chemical formula, C6H12O6, their atoms are arranged differently, giving them distinct structures and properties.
From Monomers to Complex Carbohydrates
Monosaccharides can join together to form larger carbohydrate molecules through a process called dehydration synthesis, also known as a condensation reaction. During this reaction, a molecule of water is removed as a chemical bond, specifically a glycosidic bond, forms between two monosaccharides.
When two monosaccharides bond, they form a disaccharide. Common examples include sucrose (table sugar), which is formed from glucose and fructose, and lactose (milk sugar), composed of glucose and galactose. Maltose, often called malt sugar, is another disaccharide consisting of two glucose units linked together. Beyond disaccharides, many monosaccharide units can link to create polysaccharides, which are large, complex carbohydrates.
Polysaccharides serve diverse roles, including energy storage and structural support within living organisms. Starch, for instance, functions as the primary energy storage in plants, while glycogen serves a similar purpose in animals, stored mainly in the liver and muscles. Cellulose provides structural support, forming the cell walls of plants.