Problem 2 - Campbell Biology

Question

The enzyme amylase can break glycosidic linkages between glucose monomers only if the monomers are in the \(\alpha\) form. Which of the following could amylase break down? (A) glycogen, starch, and amylopectin (B) glycogen and cellulose (C) cellulose and chitin (D) starch, chitin, and cellulose

Step-by-Step Solution

Answer

Option (A) glycogen, starch, and amylopectin.

Step 1: Understanding Glycosidic Linkages

Glycosidic linkages are bonds that connect glucose monomers in polysaccharides. In the \(\alpha\) form, the -OH group attached to the 1st carbon atom of glucose is below the plane of the ring.

Step 2: Identifying Polysaccharides with \(\alpha\) Linkages

Amylase can only break down polysaccharides with \(\alpha\)-glycosidic linkages. These include glycogen, starch, and amylopectin.

Step 3: Eliminating Polysaccharides with \(\beta\) Linkages

Polysaccharides like cellulose and chitin have \(\beta\)-glycosidic linkages, where the -OH group on the 1st carbon is above the plane of the ring. Therefore, amylase cannot break these down.

Step 4: Choosing the Correct Answer

Based on the analysis, amylase can break down glycogen, starch, and amylopectin, which are all listed in option (A).

Key Concepts

Enzyme Specificity

Enzymes are proteins that act as biological catalysts, speeding up chemical reactions in the body. They are highly specific, meaning that each enzyme only catalyzes one kind of reaction or a reaction involving a specific type of molecule. This specificity is based on the enzyme's active site and the shape of the molecule it interacts with, known as the substrate. In the exercise, amylase is an enzyme that specifically targets glycosidic linkages in \(\frac{\beta}{\beta-alpha}\) glucose monomers. This means amylase can only break down polysaccharides like glycogen, starch, and amylopectin, which have \(\frac{\beta}{\beta-alpha}\)-glycosidic linkages.

Glucose Monomers

Glucose monomers are the building blocks of various polysaccharides. They can exist in two main forms: \(\frac{\beta}{\beta-alpha}\) and \(\beta-beta}\). In the \(\frac{\beta}{\beta-alpha}\) form, the -OH group attached to the 1st carbon atom is below the plane of the ring, while in the \(\beta-\beta}\) form, it is above the plane. The arrangement of these -OH groups is crucial because it dictates the type of glycosidic linkage formed. Amylase can only break down polysaccharides with \(\frac{\beta}{\beta-alpha}\)-glycosidic linkages, which include glycogen, starch, and amylopectin. This is due to the enzyme's specificity for the \(\frac{\beta}{beta-alpha}\) configuration.

Polysaccharides

Polysaccharides are large molecules made up of many glucose monomers linked by glycosidic bonds. They play various roles in living organisms, primarily as energy storage or structural components. Common polysaccharides include:

• Glycogen: An energy storage molecule in animals, composed of \(\frac{\beta}{\beta-alpha}\)-glycosidic linkages.
• Starch: An energy storage molecule in plants, also composed of \(\frac{\beta}{\beta-alpha}\)-glycosidic linkages and includes amylose and amylopectin.
• Cellulose: A structural component in plant cell walls composed of \(\frac{\beta}{\beta-beta}\)-glycosidic linkages, making it indigestible by human enzymes like amylase.
• Chitin: A structural component in the exoskeletons of arthropods, also having \(\frac{\beta}{\beta-beta}\)-glycosidic linkages.

Since amylase can only target \(\frac{\beta}{beta-alpha}\)-glycosidic linkages, it effectively breaks down glycogen, starch (amylose, and amylopectin), but not cellulose or chitin.