The key difference between D and L glucose is that in D-glucose, three hydroxyl groups and one hydrogen group are in the right side whereas, in L-glucose, the three hydroxyl groups and one hydrogen group are in the left side.
The “D” and “L” letter indication in the names of D-glucose and L-glucose are used to distinguish the structural differences in the glucose molecule. These two forms are called enantiomers because their molecular structures are mirror images of each other. Therefore, the key difference between D and L glucose lies in their structure. We can explain the differences in their shapes using the Fisher projection model; it is one of the ways of drawing organic molecules.
CONTENTS
1. Overview and Key Difference
2. What is D Glucose
3. What is L Glucose
4. Side by Side Comparison – D vs L Glucose in Tabular Form
5. Summary
What is D Glucose?
D-glucose is the enantiomer of the L-glucose and we call it dextrose. Unlike L-glucose, it occurs widely in nature. Moreover, this compound is the most extensively important aldohexose in living organisms. For example, it is important as an energy source in most living organisms ranging from bacteria to human.
Figure 01: D and L Glucose Structures
These organisms get energy from this compound through aerobic or anaerobic respiration or fermentation.
What is L Glucose?
L-glucose is an organic compound and its IUPAC name is (2S,3R,4S,5S)-2,3,4,5,6-pentahydroxyhexanal. Its molecular formula and molecular weights are C6H12O6 and 180.16 gmol-1 respectively. This compound naturally occurs in fruits and other parts of plants in its free state. However, it is not present in higher living organisms.
But, we can synthetically produce it in the laboratory. This compound has a similar taste which is equivalent to the taste of D-glucose. Living organisms cannot consume it as their energy source because it is not phosphorylated by hexokinase, which is the first enzyme in the glycolysis pathway.
What is the Difference Between D and L Glucose?
D-glucose is the enantiomer of the L-glucose and we call it dextrose. L-glucose is an organic compound and its IUPAC name is (2S,3R,4S,5S)-2,3,4,5,6-pentahydroxyhexanal. In D-glucose, three hydroxyl groups and one hydrogen group attach to the right side whereas, in L-glucose, three hydroxyl groups and one hydrogen group attach to the left side.
Furthermore, D-glucose can exist in both linear form and cyclic form, but L-glucose exists in an equilibrium mixture of α-L-glucopyranose and β-L-glucopyranose. D-glucose is the main energy source in most of the living organisms. However, L-Glucose is a low-calorie sweetener that is a good suggestion for diabetes patients.
Summary – D vs L Glucose
The “D” and “L” letter indication in the names of D-glucose and L-glucose are useful to distinguish the structural differences in the glucose molecule. The difference between D and L glucose is that in D-glucose, three hydroxyl groups and one hydrogen group are in the right side whereas, in L-glucose, the three hydroxyl groups and one hydrogen group are in the left side.