Question

Sketch a representation of sucrose and clearly label the portion that originates from glucose, the portion that originates from fructose, and the glycoside linkage between the rings.

Short answer

A representation of sucrose can be drawn as follows: \( Glucose \; \; \longrightarrow \; \; \) \( \O \! _1 \color{red}{\bigstar} \! \downarrow \! _2 \) - \( \O \! _3 \! \downarrow \! _4 \) - \( \O \! _5 \! \downarrow \! _6 \) \( \frac{||}{|||||} \) \( Fructose \;\; \longrightarrow \;\; \) \( \! _1 \! \downarrow \! _2 \color{blue}{\bigstar} \) - \( \O \! _3 \! \downarrow \! _4 \) - \( \O \! _5 \! \downarrow \! _6 \) The red star (\(\color{red}{\bigstar}\)) represents the glycoside linkage between the rings, formed by the connection between carbon 1 of glucose (α form) and carbon 2 of fructose (β form). The fructose portion is connected to the glucose portion through the glycosidic bond.

Step-by-step solution

Understand the structures of glucose and fructose

First, let's remind ourselves of the structures of glucose and fructose. Glucose is an aldohexose with the formula C6H12O6, while fructose is a ketohexose with the formula C6H12O6 as well. The difference between the two lies in the position of the carbonyl group (C=O). In glucose, the carbonyl group is at carbon 1, while in fructose, it is at carbon 2.

Identify the glycoside linkage between glucose and fructose

In sucrose, glucose and fructose are linked through their anomeric carbons (carbon 1 of glucose and carbon 2 of fructose) via a glycosidic bond. The glycoside linkage in sucrose is created by a condensation reaction, resulting in the elimination of a water molecule (H2O) and the formation of an α,1-2β linkage connecting the two monosaccharides.

Draw a representation of sucrose

Now, we can draw a representation of sucrose, showing the glucose and fructose units and the glycoside linkage between them. Please note, this is a simplified sketch, showing the rings of the sugars and the glycosidic bond: \( Glucose \; \; \longrightarrow \; \; \) \( \O \! _1 \! \downarrow \! _2 \) - \( \O \! _3 \! \downarrow \! _4 \) - \( \O \! _5 \! \downarrow \! _6 \) \( \frac{||}{|||||} \) \( Fructose \;\; \longrightarrow \;\; \) \( \! _1 \! \downarrow \! _2 \) - \( \O \! _3 \! \downarrow \! _4 \) - \( \O \! _5 \! \downarrow \! _6 \)

Label the portions of glucose, fructose, and the glycoside linkage

Now, let's label the parts of sucrose that originate from glucose, fructose, and the glycoside linkage. \( Glucose \; \; \longrightarrow \; \; \) \( \O \! _1 \color{red}{\bigstar} \! \downarrow \! _2 \) - \( \O \! _3 \! \downarrow \! _4 \) - \( \O \! _5 \! \downarrow \! _6 \) \( \frac{||}{|||||} \) \( Fructose \;\; \longrightarrow \;\; \) \( \! _1 \! \downarrow \! _2 \color{blue}{\bigstar} \) - \( \O \! _3 \! \downarrow \! _4 \) - \( \O \! _5 \! \downarrow \! _6 \) The red star (\(\color{red}{\bigstar}\)) represents the glycoside linkage between the rings, formed by the connection between carbon 1 of glucose (α form) and carbon 2 of fructose (β form). The fructose portion is connected to the glucose portion through the glycosidic bond.

Key concepts

Understanding the Glucose Structure

Glucose is a simple sugar that plays an essential role in living organisms as an energy source. It is classified as an aldohexose, meaning it has six carbon atoms and contains an aldehyde group.
The chemical formula for glucose is \( \text{C}_6\text{H}_{12}\text{O}_6 \), and its structure can be represented in a ring form, most commonly as a six-membered pyranose ring.

• In the pyranose form, five carbon atoms and one oxygen atom form the ring, with the aldehyde group having undergone a reaction with one of the hydroxyl groups to close the ring.
• The first carbon atom in glucose is referred to as the anomeric carbon, and it plays a crucial role in linking to other sugars.

Understanding the structure of glucose is fundamental in learning about other disaccharides, like sucrose, where glucose forms one of the building blocks.

Exploring the Fructose Structure

Fructose is another simple sugar found in many plants and is often bonded with glucose to form the disaccharide sucrose. Unlike glucose, fructose is a ketohexose, which means it has six carbon atoms and a ketone group.
Similar to glucose, its chemical formula is also \( \text{C}_6\text{H}_{12}\text{O}_6 \), but its atoms are arranged differently.

• The ketone group of fructose is located at the second carbon atom rather than the first, as seen in glucose.
• In its cyclic form, fructose usually forms a five-membered ring, known as a furanose ring.
• The second carbon atom is the anomeric carbon, crucial for forming bonds with other sugars.

Having an understanding of fructose's structure helps us recognize how it pairs with glucose to form compounds like sucrose.

The Role of Glycosidic Bonds

A glycosidic bond is a type of covalent bond that links a carbohydrate molecule to another group, which could be another sugar. These bonds are vital in the structure of polysaccharides and disaccharides like sucrose.
To form a glycosidic bond, a condensation reaction takes place, where a molecule of water is released.

• In sucrose, a glycosidic bond is formed between the anomeric carbon of glucose (carbon 1) and the anomeric carbon of fructose (carbon 2).
• The linkage between these two sugars is specifically known as an \( \alpha, 1-2 \beta \) glycosidic bond.
• This bond type not only serves as a connection between sugars but also influences the sweetness and digestibility of the molecule.

Recognizing the importance of glycosidic bonds is fundamental to understanding how different sugars combine and interact.