An Introduction to Glucose Molecules: Alpha Vs Beta Glucose
Let’s us understand the structure, function, and type of Glucose molecule before analysing the difference between Alpha and Beta Glucose.
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Definition of Glucose
Glucose is a type of sugar with the molecular formula C₆H₁₂O₆, being a subclass of carbohydrates, and the most abundant one amongst the monosaccharides. Mainly utilized by plants and most algae as an input for photosynthesis and water and carbon dioxide to produce the world’s most abundant carbohydrate, cellulose.
Functions of Glucose
Of all the nutrients, glucose is the most significant source of energy for metabolism in organisms. Glucose is stored as a polymer, primarily as starch and amylopectin in plants and glycogen in animals, for metabolic usage. Blood sugar is the other name for glucose in the blood of animals. The synthetic stereoisomer of glucose, l-glucose, is synthesized in relatively minute quantities and is less physiologically active than the natural form, d-glucose.
Types of Glucose
- D-Glucose
- Beta-D-Glucopyranose
- Alpha-D-Glucopyranose
What is Alpha and Beta Glucose?
Alpha Glucose:
The other isomer of dextrose(D) glucose is alpha(D) glucose where the -OH group pairs are in position 1 and position 4 on one side of the plane. It can be termed as an anomer where the (-CH₂OH) group is adjacent to the hydroxyl group at the first position. Due to the steric hinderance developed due to the presence of the OH groups on the same sides of this glucose isomer, this glucose isomer is less stable than beta(D) glucose.
Properties of Alpha Glucose
There is 36% more of alpha-glucose available in nature. Typically, alpha-glucose is much more reactive than beta-glucose due to the position of the hydroxyl group which largely determines the properties of a molecule. It has a specific rotation of 112.2° and melting point of 146°C. Besides that it can crystallise as alpha-glucopyranose from its aqueous solution.
Beta Glucose:
Beta glucose is another dextrose(D) glucose isomer. It can be recognized as comprising hydroxyl (-OH) groups on its 1 and 4-position, which are on opposite sides of the molecule. The -OH group at position 1 is on the same side of the molecule as that of (-CH₂OH).
Properties of Beta Glucose
Beta glucose is more stable as less steric hindrance with bulky groups separated from each other. Hence beta glucose occurs naturally 64%. The specific rotation for beta glucose is 18.7° and melting point is 150 °C. From aqueous solutions beta-glucose can be crystallized as beta-glucopyranose and beta-glucopyranose hydrate.
Alpha and Beta Glucose Difference
| S.No |
Category |
Alpha Glucose |
Beta Glucose |
| Definition | 1 and 4 hydroxyl groups are located on the same side. | 1 and 4 hydroxyl groups are located on the opposite side. | |
| Energy level | Alpha glucose has high energy. | Beta glucose has low energy. | |
| 1 | Stability | Alpha glucose has low stability. | Beta glucose has high stability. |
| 2 | Melting Point | 146⁰C | 150⁰C |
| 3 | Polymerisation | Results in the formation of starch. | Results in the formation of cellulose. |
| 4 | Specific Rotation | 112.2⁰ | 18.7⁰ |
| 5 | Sources | Beans, Corn, Sucrose, Potato | Algae, Mushroom, Legumes, Nuts |
Summary
The only chemical difference between alpha and beta glucose is the positioning of the -OH (hydroxyl) and -H (hydrogen) groups on carbon 1. Whereas in beta glucose the -OH is attached above the ring, the -OH on alpha glucose is attached below the ring.
