Chapter 24 Carbohydrates

Chapter 24 Carbohydrates - Chemistry 140C Winter 2010 (K....

Info iconThis preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
Chemistry 140C Winter 2010 (K. Albizati) 1 Chapter 24 - Carbohydrates To most people, the term “sugar” refers to that sweet, white granular material we put in coffee, tea and in our baked goods. This kind of sugar is an example of an important class of biomolecules called “carbohydrates.” Carbohydrate is the general term for a class of biomolecules which are essentially poly-hydroxy aldehydes and poly-hydroxyketones. Carbohydrates play a variety of roles in biochemistry and human biology. Some terms that are used interchangeably: CARBOHYDRATE = SUGAR = SACCHARIDE All refer generally to poly-hydroxy aldehydes and ketones. We will concentrate our study on those carbohydrates that are naturally-occurring and therefore important in biology and medicine. Classification and Nomenclature Best to start out just looking at some examples. By far, the most important carbohydrate is glucose: This is the general form of a monosaccharide they have one carbonyl group (aldehyde, ketone or acid) and the remaining carbons each bear one hydroxyl. Monosaccharides can be linked together via ether and/or acetal bonds to form very large polymers called polysaccharides. A disaccharide consists of 2 linked monosaccharides and so on.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Chemistry 140C Winter 2010 (K. Albizati) 2 Almost all saccharides in nature have at least one chiral carbon and they occur in nature as a single enantiomer. Glucose has 4 chiral carbons and has 15 other stereoisomers for a total of 16 possible stereoisomers of this gross structural formula. The suffix –ose is often used in describing and naming carbohydrates. For example: - a carbohydrate with 6 carbons is called a hexose - a carbohydrate with 5 carbons is called a pentose - a carbohydrate with an aldehyde as its carbonyl unit is called an aldose - a carbohydrate with a ketone as its carbonyl unit is called a ketose Glucose is an “aldohexose.” What is a 3 carbon carbohydrate with a ketone called? There is only one of those and it is 1,3-dihydoxyacetone. The isomeric 3 carbon carbohydrate is glyceraldehyde: Look at glyceraldehyde more closely: Naturally-occurring glyceraldehyde has an R-configured chiral carbon. Using nomenclature which dates back nearly a hundred years, we call this D- glyceraldehyde. The opposite enantiomer is called L-glyceraldehyde. The D and the L refer to the configuration of the highest numbered chiral carbon when viewed in a Fischer configuration. D- has the hydroxyl on the right side and L has the hydroxyl on the left side.
Background image of page 2
Winter 2010 (K. Albizati) 3 So…… D or L series? Almost all naturally occurring carbohydrates are of D-configuration. The downside to nomenclature of carbohydrates is that it is dominated by specific common names. The two upsides are that there are not that many biologically important carbohydrates to know and understand and they are frequently found on food ingredient labels so you can recognize a carbohydrate by name in your diet. So let’s look at the important aldoses and ketoses.
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 25

Chapter 24 Carbohydrates - Chemistry 140C Winter 2010 (K....

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online