Chemical Digestion of Carbohydrates: Definition & Process

Digestion

The calories that you consume during the day basically consist of a combination of three main nutrients, called carbohydrates, proteins and fats. When you sit down to a meal, you probably do not give much thought to what happens to these nutrients as they make their way through your digestive tract. But when we take a closer look, we see that each of these nutrients is made up of long chains of subunits that must be chemically broken down by enzymes.

Nutrients are made up of long chains of subunits that must be broken down by enzymes

These nutrients must be broken down so they are small enough to be absorbed out of your digestive tract, otherwise they would pass right through you, and you would suffer from malnutrition. This lesson will focus on carbohydrates. Carbohydrates are organic compounds, including sugars and starches, that serve as a major energy source for your body. In this lesson, you will learn how the carbohydrates that you eat are broken down in your digestive tract.

Monosaccharides

The basic building blocks of any carbohydrate, whether it is bread, a baked potato or a plate of pasta, are called monosaccharides. Monosaccharides are defined as simple sugars because they are in their simplest form and cannot be broken down more than they already are. In fact, their name is very descriptive. We see that the prefix 'mono' means one, and the suffix 'saccharide' means sugar. So, a monosaccharide is literally 'one sugar,' standing by itself, with no other units attached to it.

Monosaccharides are the basic building blocks of carbohydrates

There are three common monosaccharides in your diet. They are called glucose, fructose and galactose. Of these three, glucose is the most important, and when we talk about blood sugar levels, we are referring to glucose. Glucose is also a major energy source for your body cells.

Disaccharides and Polysaccharides

When you join a couple of monosaccharides together you form a disaccharide. The prefix 'di' means two, and disaccharides are defined as a class of sugars that are composed of two monosaccharides, basically a 'double sugar.' There are three common disaccharides in your diet, and we call them sucrose, lactose and maltose.

There is one more type of carbohydrate that your digestive system is able to digest and break down into a monosaccharide, and that is starch. Starch is a polysaccharide. The prefix 'poly' means many, and polysaccharides are defined as a class of sugars that are composed of many monosaccharides.

There is another type of polysaccharide that you eat called cellulose. Cellulose is found in foods, such as fruits, vegetables and grains, but your body does not have the enzymes that it needs to break down cellulose. Therefore, we do not get nutrients from cellulose, but these foods do provide us with fiber. Fiber cannot be digested but helps the body move food through the digestive tract. Fiber is almost like a scrub brush that moves through your intestine and keeps food remnants moving along their path.

Cellulose provides us with fiber, which cannot be digested but helps food move through the digestive tract

Hydrolysis

The digestive tract can be thought of as a disassembly line because food moves from one area to the next and is broken down bit by bit. When you eat, your body takes disaccharides and polysaccharides, and it breaks them down into monosaccharides. It is necessary for this breakdown to occur so the sugar units are small enough to be absorbed out of your digestive tract and into your bloodstream. Carbohydrates are disassembled, or broken down, by a process called hydrolysis. Hydrolysis is the breakdown of a chemical compound that involves splitting a bond by water. The term is easy to recall if you remember that 'hydro' means water and 'lysis' means to loosen or break. So, hydrolysis is the process by which a water molecule comes in and breaks the bond between sugars. For example, as a water molecule (H2O) is added to the bonds that hold a starch together, the bonds are broken. The result is individual monosaccharides. These monosaccharides are now small enough to pass through your intestinal mucosa and into your bloodstream.

In hydrolysis, water breaks the bonds in carbohydrates

Lesson Summary

Let's review: carbohydrates are organic compounds, including sugars and starches, that serve as a major energy source for your body. The basic building blocks of any carbohydrate are called monosaccharides, or simple sugars. When two monosaccharides are joined together, they form disaccharides. And when many monosaccharides are joined together, they form polysaccharides. Disaccharides and polysaccharides must be broken down to monosaccharides by hydrolysis so they are small enough to be absorbed. Hydrolysis is the breakdown of a chemical compound that involves splitting a bond by water. There are polysaccharides that your body cannot break down called cellulose. But cellulose is still valuable because it provides your body with fiber. Fiber helps the body move food through the digestive tract, somewhat like a scrub brush.

Learning Outcome

At the end of this lesson, you should be able to:

• Define what carbohydrates are
• Identify the basic building blocks of carbohydrates
• Identify the three most common monosaccharides
• Discuss disaccharides and polysaccharides
• Identify the three most common disaccharides
• Describe what happens during hydrolysis