Lactose Intolerance and the Major Disaccharides: Definition, Structure & Examples Video

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  • 0:05 Saccharides
  • 1:44 Disaccharides
  • 3:05 Lactose Intolerance
  • 4:40 Lesson Summary
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Lesson Transcript
Instructor: Rebecca Gillaspy

Dr. Gillaspy has taught health science at University of Phoenix and Ashford University and has a degree from Palmer College of Chiropractic.

Disaccharides are a class of sugar created by the combination of two monosaccharides. The three major disaccharides in your diet are maltose, sucrose, and lactose. In this lesson, you will learn about these disaccharides and a common digestive system disorder called lactose intolerance.


In biochemistry, carbohydrates are viewed as molecules, such as saccharides.

When you think of carbohydrates, you probably think of starchy foods such as pasta or bread. Or, maybe you think of simple carbs, like candy and cookies.

While these are all examples of carbohydrate foods, in biochemistry, we tend to look at carbohydrates as molecules like saccharides, which are basically sugars. In this lesson, we will learn about some of the properties of saccharides and how they are linked together to form disaccharides. We will also learn about lactose intolerance, which is a disorder that some people suffer from when they eat a certain type of disaccharide.

Saccharides are molecules comprised of carbon, hydrogen, and oxygen atoms. A monosaccharide is one sugar unit. This is an easy term to recall because we see that the prefix 'mono' means one and the suffix 'saccharide' of course means sugar.

Because monosaccharides are the smallest sugars and because they are the basic building blocks of all larger and more complex sugars, we often refer to them as simple sugars. There are three dietary monosaccharides that we will consider. The first is called glucose. This is the most important sugar in your body because it is used as fuel by all of your body cells. Glucose is also found in your blood and therefore referred to as blood sugar.

Fructose is another dietary monosaccharide and is the most abundant sugar in fruit. We also see galactose, which is found in milk. These monosaccharides each have their own unique chemical structure, but we notice that the thing they have in common is that they are all single-ring structures.


In dehydration synthesis, water is removed and two monosaccharides become a disaccharide.
Dehydration Synthesis

We can take these single-ring structures and combine them by taking away water, or H2O. This combining of molecules by removing water is a chemical reaction called dehydration synthesis. For instance, we can put two monosaccharides together and create a two-sugar molecule called a disaccharide. We see that 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 major disaccharides in your diet, and they are formed when we stick together the three monosaccharides in different combinations.

For instance, we can take two glucose monosaccharides, remove a water or H2O molecule, and create the disaccharide maltose. Therefore, maltose is glucose + glucose. Maltose is commonly referred to as malt sugar, and it is the sugar that we get when we eat starches and they break down in our digestive tract.

We can create sucrose from the linkage of glucose + fructose. Sucrose is the white, sweet tasting, crystalline powder that you know as table sugar.

And, we can create lactose from the linkage of glucose + galactose. Lactose is also referred to as milk sugar because it is found in milk as well as other dairy products.

Lactose, which is made by linking glucose and galactose, is one of the three major disaccharides.

Lactose Intolerance

Because lactose is a double sugar, or disaccharide, it is too big to pass through the lining of your digestive tract when you consume it. Therefore, it must be broken down into its monosaccharide units to be absorbed out of your digestive tract and into your bloodstream.

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