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Carbohydrate Classification


MCAT Biochemistry

Carbohydrate classification concerns the names and structures of some of the most important carbohydrate molecules. Carbohydrates are organic compounds composed of carbon chains bound to hydrogen and oxygen. Monosaccharides, also called simple sugars, can be classified by the number of carbons they contain, such as trioses, tetroses, pentoses, and hexoses. Carbohydrates can also be classified by their most oxidized functional group, with aldoses having an aldehyde and ketoses having a ketone as the most oxidized functional group.

Cyclic aldoses form structures called hemiacetals, and cyclic ketoses form structures called hemiketals, with 6-membered rings called pyranoses and 5-membered rings called furanoses. Moving on to more complex carbohydrates, disaccharides consist of two monosaccharides bonded via glycosidic linkages, with sucrose, lactose, and maltose being important examples. Lastly, polysaccharides, such as cellulose, starch, and glycogen, are long chains of linked monosaccharides playing significant roles in metabolism and energy storage.

Lesson Outline

<ul> <li>Carbohydrates: organic compounds composed of carbon chains bound to hydrogen and oxygen</li> <li>Monosaccharides: carbohydrate monomers</li> <ul> <li>Simple sugars are classified based on the number of carbons they contain</li> <li>Aldoses: carbohydrates with an aldehyde as the most oxidized functional group</li> <li>Ketoses: carbohydrates with a ketone as the most oxidized functional group</li> <li>Examples of important monosaccharides: glyceraldehyde, glucose, galactose, mannose, and fructose</li> </ul> <li>Cyclic ring structures</li> <ul> <li>6-membered rings: pyranoses</li> <li>5-membered rings: furanoses</li> </ul> <li>Disaccharides: two monosaccharides bonded via glycosidic linkages</li> <ul> <li>Important disaccharides: sucrose, lactose, and maltose</li> </ul> <li>Polysaccharides: long chains of linked monosaccharides</li> <ul> <li>Metabolically important polysaccharides: cellulose, starch, and glycogen</li> </ul> </ul>

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What are the main categories of carbohydrate classification?

Carbohydrates are classified into three main categories: monosaccharides, disaccharides, and polysaccharides. Monosaccharides are simple sugars, like glucose, fructose, and galactose. Disaccharides are composed of two monosaccharides joined together, such as sucrose, lactose, and maltose. Polysaccharides are complex carbohydrates that consist of more than 10 monosaccharide units, examples include starch, glycogen, and cellulose.

How are monosaccharides further classified as aldoses or ketoses?

Monosaccharides are further classified as aldoses or ketoses based on their functional groups. Aldoses have an aldehyde functional group (a carbonyl group at the end of the carbon chain) in their open-chain form. Ketoses have a ketone functional group (a carbonyl group in the middle of the carbon chain) in their open-chain form. For example, glucose and galactose are aldoses, while fructose is a ketose.

What are the differences between glucose, fructose, and galactose?

Glucose, fructose, and galactose are all hexose monosaccharides with the same molecular formula (C6H12O6), but they differ in their structure and properties. Glucose has an aldehyde functional group and is an aldose. It is the most important carbohydrate in terms of energy production in living cells. Fructose is a ketohexose (hexose ketone) with a ketone functional group and is found in high concentrations in fruits and honey. Galactose is an aldohexose (hexose aldose), like glucose, but it has a different stereochemistry and is predominantly found in dairy products. Its primary role is to form lactose when combined with glucose.

What role does glycogen play in carbohydrate storage and metabolism?

Glycogen is a large, branched polysaccharide made of glucose units. It serves as the primary storage form of carbohydrates in animals. Glycogen is synthesized and stored mainly in the liver and muscle cells. During periods of high energy demand or low glucose availability, glycogen is broken down into glucose to meet the body's energy needs. Thus, glycogen plays a crucial role in maintaining glucose homeostasis and energy metabolism in the body.

How are disaccharides formed and what are some common examples?

Disaccharides are formed through a condensation reaction, which joins two monosaccharide units through a glycosidic bond. This reaction involves the loss of a water molecule during the process. Some common examples of disaccharides include sucrose (glucose + fructose), lactose (glucose + galactose), and maltose (glucose + glucose).