Structure of Glucose and Fructose

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Glucose vs Fructose

Glucose

It is defined as a monosaccharide and is found in all primary carbohydrates such as table sugar starch. It is also called grape sugar or blood sugar. It is represented as a six-membered ring and forms a pyranose ring structure. It is aldohexose and is the primary and preferred energy source of the body. The starch compound contains glucose.


Fructose

It is defined as a monosaccharide and is found in fruits and vegetables. The glycemic index is lower in fructose to that of glucose. Binding fructose to cellular protein is seven times faster compared to the glucose. Fructose is also referred to as D- fructose or fruit sugar and its functional group are called a ketone. It is primarily metabolized in the liver and is not found in starch.


Structure of Glucose

Glucose is defined as a group of carbohydrates, a simple sugar having a chemical formula C6H12O6. It is composed of six carbon atoms, including an aldehyde group. Thus, we can refer to this as an aldohexose. It exists in two forms, which are either in the open-chain (acyclic) form or ring (cyclic) form. The major source of energy needed for living organisms is given as glucose. Algae and plants prepare glucose during the photosynthesis process with the help of water, carbon dioxide, and sunlight. It is naturally found in honey and fruits. The glycogenolysis process obtains glucose present in animals.


  1. Steps to Draw an Open-Chain Structure of the Glucose Molecule

Follow the below steps to draw an acyclic form of glucose.

Step 1: First, draw six carbon atoms

Step 2: Now, draw extended arms for all the carbon atoms ignoring the first one.

Step 3: Now draw a hydrogen atom to carbon bond such that four will be on one side, one on the other side.

Step 4: Rest of the spaces should be filled with an OH group. (as importantly – transpose (OH) to —> (HO) for the left side to represent that oxygen is bonded to carbon)

Step 5: Complete both the ends with two single-bonded hydrogen bonds with one double-bonded carbon.

Baeyer showed the open-chain structure of the glucose compound. However, these structures have faced difficulties in explaining why glucose fails to react with Schiff base, sodium bisulphate or the mutarotation process. Haworth introduced the cyclic structure of glucose that confirms the existence of alpha and beta forms of mutarotation, glucose, and more.

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  1. Steps to Draw the Ring Structure of a Glucose Molecule

Follow the below steps to draw a cyclic form of glucose.

Step 1: Firstly, construct a hexagon

Step 2: Then, draw carbon atoms at five consecutive edges.

Step 3: Thereafter, attach an oxygen atom at the left out edge.

Step 4: Now, attach the four carbon atoms with OH and H groups.

Step 5: Complete the entire structure by attaching the left out carbon atom to two hydrogen atoms, one carbon atom and OH group.

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Glucose Properties

Glucose Chemical Formula

C6H12O6

Glucose Molar mass

180.156 g/mol

IUPAC Name

D-Glucose


Fructose Ring Structure

Fructose is described as a monosaccharide which is given as a simple sugar having a chemical formula C6H12O6. It is also known as fruit sugar and was discovered in 1847 by a French chemist named Augustin-Pierre Dubrunfaut. It is composed of a 6-carbon polyhydroxy ketone.

Crystalline fructose takes place as a cyclic six-membered structure, which is delinquent to the stability of the internal hydrogen-bonding and hemiketal. This form is known as D-fructopyranose. It primarily takes place in vine fruits, honey, most root vegetables, flowers, and berries. It can be obtained Commercially from maize, sugar beets, and sugar cane.


Open Chain structure and Ring Structure of a Fructose Molecule

The cyclic structure of fructose is given below:

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The Fischer projections of D-fructose and L-fructose can be given as follows:

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Fructose Properties

Dry fructose appears as a white coloured crystalline solid, which is odourless and sweet. It is soluble in ether, water, and alcohol.


Properties of Fructose

Fructose Molar mass

180.156 g/mol

Fructose Formula

C6H12O6

Density

1.694 g/cm3

Fructose Chemical Formula

C6H12O6

Melting point

103°C


The Structural Difference Between the Glucose and Fructose Compounds

Glucose and fructose are defined as constitutional isomers, which means that there is a difference in bond connectivity. Glucose is defined as an aldehyde, whereas fructose is defined as a ketone. So, when they become cyclicized by the formation of hemiketal/hemiacetal, glucose is a 6-ring sugar; on the other side, fructose is a five-ring sugar. We should also know that glucose is the preferred form of energy of the body and that every cell can metabolize the glucose compound. Only, the liver can metabolize fructose, that is why we should not intake much quantity of it.


D-Glucose vs L-Glucose

D-Glucose Chemistry

In the glucose molecule, a hydrogen and oxygen atom group is bonded to the carbon atom. On the other side of the glucose molecule, there exists a double-bonded oxygen atom. Looking at the D-glucose’s Fisher model with the double-bonded oxygen atom, which is pointed down, the hydrogen and oxygen group present at the top of the atom points towards the right.


L-Glucose Chemistry

D-glucose and L-glucose are composed of similar atoms. The only difference between these two structures can be displayed using the Fisher model. In the Fisher model, unlike D-glucose, the hydrogen and oxygen group of atoms present in L-glucose points to the left. If these two specific molecules faced each other, they would look like a reflection of one another.


FAQ (Frequently Asked Questions)

1. What are fructose and glucose?

Both the compounds fructose and glucose are given as simple sugars or monosaccharides. When these compounds are digested, both sugar and starch, whether high-fructose corn syrup (HCFS) or sucrose, produce excess quantities of glucose.

2. Explain various types of glucose?

The d-isomer, d-glucose, which is also called dextrose, is commonly found in nature, but the l-glucose, l-isomer, is not found commonly in nature. Hydrolysis of carbohydrates like plant sugar (sacrose), dairy sugar (lactose), cellulose, maltose, glycogen is used to obtain glucose.

3. Where does glucose produce from?

The food we consume is produced either from sugar or glucose. The prevalent sources of glucose are given as carbohydrates, such as bread pasta, cereals. In our stomachs, these types of foods are split into sugar, and then they are absorbed into the bloodstream.

4. Why is Glucose a monosaccharide?

Monosaccharides (to explain clearly, mono- = “one;” sacchar- = “sugar”) are given as simple sugars, where glucose is the most prevalent compound.

5. What is the function of fructose?

Similar to glucose, fructose also provides energy cells. These cells process fructose to gain energy using a method known as aerobic breathing, that primarily involves burning fructose in the presence of oxygen to generate ATP, which is the molecule of cellular energy.