Disaccharides: Definition, Structure, Types & Examples

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  • 0:01 What is a Disaccharide?
  • 1:19 Building Blocks of…
  • 2:11 Common Disaccharides
  • 3:00 Hydrolysis & Lactose…
  • 3:48 Other Disaccharides
  • 4:20 Lesson Summary
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Lesson Transcript
Instructor: Thomas Higginbotham

Tom has taught math / science at secondary & post-secondary, and a K-12 school administrator. He has a B.S. in Biology and a PhD in Curriculum & Instruction.

Disaccharides are among the most commonly known and encountered sugars, including sucrose (table sugar) and lactose, the discomfort-causing sugar in milk. In this lesson, learn what disaccharides are and how they are structured.

What Is a Disaccharide?

If you look on the side of a cereal box, you will see the broad category of carbohydrates, which is further broken down into several categories, including fiber and sugars. Those sugars are one example of a disaccharide, sucrose.

But what is a disaccharide? As you might suspect based on the di- meaning 'two' prefix, a disaccharide is two monosaccharides combined into one. More specifically, a disaccharide results when two monosaccharides are joined in a chemical process called dehydration synthesis, which causes two monosaccharides to combine, losing a water molecule in the process. This process is also known as a condensation reaction. Here we see an example of the formation of the disaccharide sucrose, formed from the combination of the monosaccharides fructose and glucose.

All carbohydrates are made up of carbon, hydrogen, and oxygen and follow the chemical formula Cx(H2O)y. For example, the carbohydrate D-Glucose has a chemical formula of C6H12O6 and the carbohydrate that is regular table sugar has a chemical formula C12H22O11.

Building Blocks of Disaccharides

To understand the nature and impact of disaccharides, it is helpful to know a little about their monosaccharide building blocks, or simple sugars. The most common monosaccharides are glucose, galactose, and fructose. Glucose is the body's primary fuel source, used to produce the energy molecule adenosine triphosphate, or ATP, through cellular respiration. Fructose is a monosaccharide commonly found in fruits.

As you may be able to tell by comparing this image of the monosaccharide glucose to the previous image of the disaccharide sucrose, monosaccharides are smaller than disaccharides, which is one of the reasons monosaccharides are able to be directly absorbed into the bloodstream through the digestive tract. This is important to note and is especially relevant when we look at what happens to people with lactose intolerance.

Common Disaccharides

Disaccharides are generally water-soluble and sweet when ingested. Because they are made of the combination of two simple sugars, you might correctly guess that disaccharides are known as complex sugars. Let's take a look at some of the most commonly encountered disaccharides and the two monosaccharides from which they're made. Again, these complex sugars are created through dehydration synthesis, or condensation reaction:

  • Sucrose (table sugar) comes from glucose and fructose joining
  • Lactose (milk sugar) comes from glucose and galactose joining
  • Maltose (malt or beer sugar) comes from two glucose molecules joining

You may have noticed that most sugars, whether simple or complex, end with the suffix -ose.

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