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Structure of Glucose and Fructose, Cyclic and Open Chain
IMPORTANT LINKS
Biomolecules
Glucose and fructose are two important simple sugars that you’ll often come across in biology and chemistry. They are both monosaccharides, meaning they are made of just one sugar unit.
These sugars can exorcist in two forms: a straight (open chain) form and ring shaped (cyclic) from. Understanding both structures is important because they help explain how these sugars behave in the body and in chemical reactions. In this article, we’ll learn about the open chain and cyclic structures of glucose and fructose in a clear and easy way.
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What are Glucose and Fructose?
Glucose and fructose are simple sugars, also called monosaccharides. They both have the same chemical formula C6H12O6 but their structures are different. Glucose is an aldose sugar because it has an aldehyde group, while fructose is a ketone sugar as it contains a ketone group. These sugars are naturally found in fruits, honey, and many other foods. They give energy to our body and are important in many biological processes. Understanding their basic nature is the first step to learning their structure.
Open Chain Structure of Glucose
Glucose is an aldose sugar, which means it has an aldehyde group (CHO) at the end. In its open chain form, glucose has six carbon atoms arranged in a straight line. The first carbon (C1) has the aldehyde group, and the remaining carbons have hydroxyl groups (OH) and hydrogen atoms attached.
Steps to Draw the Open Chain Structure of Glucose:
To draw an open chain structure or acyclic structure of glucose, we need to follow these steps-
Step I- Draw 6 carbon atoms bonded to each other by a single bond in a straight chain.
Step II- Extend the remaining two bonds of four carbon atoms in the middle and attach hydrogen to one side of these carbon atoms.
Step III- For the remaining four bonds of middle carbons, attach hydroxyl groups.
Step IV- For the remaining two carbon atoms, attach two hydrogens and hydrogen to one terminal carbon.
Step V- For another terminal carbon, attach an aldehyde to the carbon atom.
Cyclic Structure of Glucose
In, solution, glucose doesn’t stay in the open chain form for long. It folds into a ring structure by a reaction between the aldehyde group (C1) and the hydroxyl group on C5, forming a six membered ring known as glucopyranose.
This ring formation is a type of intramolecular reaction called hemiacetal formation.
Steps to Draw Ring Structure of Glucose:
In order to draw a ring structure or the cyclic structure of glucose, follow undermentioned steps-
Step I- Draw a hexagon because glucose is formed of 6 carbon atoms.
Step II- At five vertices, put one carbon atom at each vertical.
Step III- On the remaining one vertice, put an oxygen atom.
Step IV- To the four carbon atoms, now attach hydrogen and hydroxyl groups, respectively.
Step V- To the remaining one carbon, attach a carbon atom bonded with hydrogen and hydroxyl groups, respectively.
Structure of Fructose
Fructose has a molecular formula C6H12O6. It is made up of 6 carbon-membered polyhydroxy ketones. It is found in fruits, honey, flowers and berries. It has two structures- an open chain structure and a ring structure (cyclic structure).
Ring and Open Chain Structure of Fructose
The ring structure of fructose is in the shape of a pentagon. The ring is made up of four carbon and oxygen atoms. The other two carbon atoms are attached to carbons bonded with oxygen atoms.
The open chain structure, also known as the fischer projection, is formed by 6 carbon-membered straight chains.
Haworth Structure of Fructose
For fructose, Haworth proposed furanose ring structures for the two anomeric forms of D (-) fructose. Furan is a structure containing a five-membered heterocyclic ring with an oxygen atom. It forms the basis of the two cyclic structures of D (-) fructose known as α – D (-) fructofuranose and β – D (-) fructofuranose.
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Key Differences Between Glucose and Fructose
Point of Difference
Glucose
Fructose
Type of Sugar
Aldose (has an aldehyde group)
Ketose (has a ketone group)
Carbonyl Group Position
On carbon 1 (C1)
On carbon 2 (C2)
Open Chain Structure
Starts with an aldehyde group
Has a ketone group in the middle
Ring Structure Name
Forms a 6-membered ring (pyranose)
Forms a 5-membered ring (furanose)
Ring Formation
Ring forms between C1 and C5
Ring forms between C2 and C5
Examples in Nature
Found in blood sugar, fruits
Found in fruits, honey
|
Point of Difference |
Glucose |
Fructose |
|
Type of Sugar |
Aldose (has an aldehyde group) |
Ketose (has a ketone group) |
|
Carbonyl Group Position |
On carbon 1 (C1) |
On carbon 2 (C2) |
|
Open Chain Structure |
Starts with an aldehyde group |
Has a ketone group in the middle |
|
Ring Structure Name |
Forms a 6-membered ring (pyranose) |
Forms a 5-membered ring (furanose) |
|
Ring Formation |
Ring forms between C1 and C5 |
Ring forms between C2 and C5 |
|
Examples in Nature |
Found in blood sugar, fruits |
Found in fruits, honey |
Importance of Open and Cyclic form
Form
Why It’s Important
Open Chain Form
- Shows the presence of aldehyde or ketone group- Helps in reactions like oxidation
Cyclic Form
- More stable and commonly found in nature- Takes part in important processes like glycolysis
Switch Between Forms
- Glucose and fructose can shift between open and cyclic forms in water- This allows flexibility in biological reactions
|
Form |
Why It’s Important |
|
Open Chain Form |
- Shows the presence of aldehyde or ketone group- Helps in reactions like oxidation |
|
Cyclic Form |
- More stable and commonly found in nature- Takes part in important processes like glycolysis |
|
Switch Between Forms |
- Glucose and fructose can shift between open and cyclic forms in water- This allows flexibility in biological reactions |
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FAQs
Why is glucose called dextrose?
Glucose is called dextrose because it is dextrorotatory i.e., as an optical isomer it rotates plane polarized light to the right and also an origin for the D designation.
What is the difference between glucose and fructose?
The primary difference between glucose and fructose is that glucose contains an aldehyde functional group, whereas fructose contains a ketone functional group.
What are the 3 types of glucose?
The three types of glucose are- α-glucopyranose, β-glucopyranose and β-glucopyranose hydrate.
Why does fructose only have 5 sides?
Fructose has a ketone functional group, and the ring closure occurs at the second carbon. In the case of fructose, a five-membered ring is formed. The hydroxyl group on the fifth carbon is converted into the ether linkage to close the ring with the second carbon atom. This makes a 5-member ring, four carbons and one oxygen.
Which one is sweeter glucose or fructose?
Fructose is sweeter than glucose. That’s why it’s often found in fruits and honey.