Carbohydrates - Monosaccharides (A-level Biology)
Carbohydrates: Monosaccharides
Simple and Complex Sugars
- Simple sugars include monosaccharides and disaccharides. Collectively these molecules are referred to as simple sugars.
- Simple sugars can function as small molecules. Monosaccharides and disaccharides can exist on their own and have many important biological roles.
- Simple sugars can also be joined to form complex sugars. Simple sugars can be utilised as monomers to make polymers called complex carbohydrates, which also have various significant biochemical roles.
Monosaccharides
- Monosaccharides are the simplest sugars. Monosaccharides just consist of a single monomer. Examples of monosaccharides are glucose, fructose, and galactose.
- Monosaccharides are organic compounds. This means that they contain the elements C and H, and additionally contain O.
Glucose
- Glucose is perhaps the most important biological monosaccharide. Glucose is crucial as it is heavily involved in respiration, the process by which living organisms generate energy.
- Glucose is a hexose sugar. This means that it consists of 6 carbon atoms.
- Glucose has two key isomers: α-glucose and β-glucose. Memorise their structures for your exam. Isomers are chemical molecules that have similar chemical formulas, but different structures due to variation in atom arrangement. Isomers can have very different functions.
In addition to α-glucose and β-glucose, there are other common and biologically relevant monosaccharides, shown in figure 2:
- Fructose is commonly found in fruits.
- Galactose is a part of the disaccharide lactose that is present in milk.
- Ribose is a pentose sugar. That means unlike glucose, it only has 5 carbon atoms. It is a common component of genes.
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