Carbohydrates: Structure and Classification
Carbohydrates are fundamental biological molecules with the general formula CH2On, where n is typically between 1 and 7. They are soluble substances that play various roles in living organisms.
Definition: Carbohydrates are organic compounds composed of carbon, hydrogen, and oxygen atoms, typically with a 2:1 ratio of hydrogen to oxygen.
Monomers and Polymers
In the context of carbohydrates A level Biology AQA, it's essential to understand the concepts of monomers and polymers:
Vocabulary: A monomer is one of many small molecules that combine to form a larger molecule polymer.
Vocabulary: A polymer is a long molecule made up of small repeating units monomers.
Classification of Carbohydrates
Carbohydrates are classified based on the number of sugar units they contain:
- Monosaccharides: Single sugar units
- Disaccharides: Two sugar units
- Polysaccharides: Long chains of sugar units
Example: Glucose C6H12O6 is an example of a monosaccharide.
Monosaccharides
Monosaccharides A Level Biology focuses on the simplest form of carbohydrates. These are sweet-tasting, soluble substances that serve as the building blocks for more complex carbohydrates.
Highlight: Common monosaccharides include glucose, fructose, and galactose.
Glucose Isomers
Glucose exists in two isomeric forms: alpha and beta glucose. These are examples of structural isomers.
Definition: Isomers are molecules with the same molecular formula but different structural arrangements of atoms.
The key difference between alpha and beta glucose lies in the position of the hydroxyl group −OH on carbon 1:
- In alpha glucose, the -OH group is below the carbon ring
- In beta glucose, the -OH group is above the carbon ring
Vocabulary: The terms "alpha" and "beta" in glucose refer to the orientation of the hydroxyl group on the anomeric carbon carbon1.
Disaccharides
Disaccharides A Level Biology covers the formation of these molecules through the combination of two monosaccharides. This process involves a condensation reaction, resulting in the formation of a glycosidic bond and the release of a water molecule.
Example: Common disaccharides include maltose glucose+glucose, sucrose glucose+fructose, and lactose glucose+galactose.
The structure of carbohydrates a level Biology curriculum emphasizes the importance of understanding these molecular arrangements and their biological significance.
