Question

What is a glycoside bond? How is it formed?

Short answer

Answer: A glycoside bond is a covalent bond that connects a carbohydrate molecule to another molecule, such as another carbohydrate or a non-carbohydrate molecule like an alcohol or an amine. It is formed through a condensation reaction, also known as a dehydration reaction, involving the following steps: 1) Protonation of the anomeric carbon of the carbohydrate, 2) nucleophilic attack by the hydroxyl group or another nucleophile of the second molecule, and 3) deprotonation with the elimination of a water molecule, resulting in the glycoside bond.

Step-by-step solution

Definition of a Glycoside Bond

A glycoside bond is a covalent bond that connects a carbohydrate (sugar) molecule to another molecule, which can be another carbohydrate or a non-carbohydrate molecule such as an alcohol or an amine. The bond is formed between the anomeric carbon (the carbon derived from a carbonyl group) of the sugar and the hydroxyl (-OH) or another functional group of the second molecule. Glycoside bonds are found in many biological molecules, such as in the structure of DNA, RNA, and polysaccharides like cellulose and starch.

Formation of a Glycoside Bond

The formation of a glycoside bond is a condensation reaction, also known as a dehydration reaction, because a water molecule is eliminated in the process. The steps involved in the formation are as follows: 1. Protonation: The anomeric carbon of the carbohydrate molecule is protonated by an acid catalyst. The protonation activates the anomeric carbon, making it more electrophilic and susceptible to nucleophilic attack. 2. Nucleophilic attack: The hydroxyl group (or another nucleophile) of the second molecule attacks the protonated anomeric carbon, forming a new bond between the molecules. 3. Deprotonation: Finally, a deprotonation step occurs, resulting in the elimination of a water molecule and the formation of the glycoside bond. Overall, the process can be summarized as follows: Carbohydrate + Alcohol/Amine ⟶ Glycoside + Water It's important to note that the formation of glycoside bonds is reversible, and the bonds can be hydrolyzed (broken) by the addition of water.