Aldose vs. Ketose Sugars

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  • 0:00 A Review of Carbohydrates
  • 1:40 Aldose: Structure and Examples
  • 2:52 Ketose: Structure and Examples
  • 3:47 Differences Between…
  • 4:31 Lesson Summary
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Lesson Transcript
Instructor: Danielle Reid

Danielle has taught middle school science and has a doctorate degree in Environmental Health

Aldose and ketose sugars are carbohydrate molecules distinctly different from one another. In this lesson, you'll learn about these sugars, discovering their unique characteristics and structure.

A Review of Carbohydrates

In the boxing ring to the right we have rough and tumble aldose. And on our left, we have light as a feather ketose! Let the games begin!

Okay, that might be a touch dramatic. Although they may not be battling one another in a boxing ring, there is a match to consider: aldose vs. ketose sugars. Before we dive into the differences between the two, let's review some basic concepts related to both sugar types.

These sugars are referred to as carbohydrates. Carbohydrates are an abundant class of organic compounds that supply energy to our body and are made of sugar units called saccharides. There are two types of carbohydrates: simple and complex. A simple carbohydrate contains only one or two sugar units. Examples of simple sugars include our friends aldose and ketose. Complex carbohydrates contain a polymer of sugar units. That is, these compounds contain long chains of sugar units linked together. Examples of two different sugars are sucrose (i.e. simple carbohydrate) and starch (i.e. complex carbohydrates).

simple vs complex

Going back to sugar units, we can classify these units (based on amount) into three categories: monosaccharides, disaccharides, and polysaccharides. For the purpose of this lesson, we will focus on monosaccharides. Aldose and ketose sugars are classified as monosaccharides. By definition, monosaccharides contain one sugar unit. Thus, you can think of a monosaccharide as another term for a simple carbohydrate. What would we then classify aldose and ketose sugars to be? That's right! They are simple carbohydrates, or monosaccharides.

Aldose: Structure and Examples

Aldose is a type of monosaccharide, or simple carbohydrate, that contains an aldehyde in its structure. In organic chemistry, an aldehyde functional group is defined by the presence of a carbon atom double bonded to an oxygen atom and single bonded to a hydrogen atom. The molecular formula for an aldehyde is RCOH. An R group is any molecule or atom that can bind to the carbonyl atom (CO), forming an aldehyde.

When you look at the term 'aldose,' think of this word as a family name that numerous sugar molecules can identify with. In other words, there are specific examples of aldose sugars. What collectively makes each example part of the aldose family is the presence of an aldehyde in its structure. Examples of these sugars include ribose and glyceraldehyde.

An aldose sugar that has three or more carbon atoms is characterized as possessing stereoisomerism. A stereoisomer is a type of isomer that differs because of spacial orientation as opposed to atom connectivity within the structure. A feature for the structure of aldose is its ability to react and form a cyclic ring. For example, the aldose sugar glucose can react with an acid to form the cyclic aldose sugar glucopyranose.

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