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: Identify the Requirement for Breakdown

The enzyme amylase can only break down glycosidic linkages between glucose monomers if the monomers are in the \( \alpha \) form.

Step 2: Analyze Each Option

Determine which polysaccharides contain glucose monomers in the \( \alpha \) form:Option (A) glycogen, starch, and amylopectin - All three contain glucose monomers in the \( \alpha \) form.Option (B) glycogen and cellulose - Glycogen contains \( \alpha \) form glucose monomers, but cellulose contains \( \beta \) form.Option (C) cellulose and chitin - Both cellulose and chitin contain glucose monomers in the \( \beta \) form.Option (D) starch, chitin, and cellulose - Starch contains \( \alpha \) form glucose monomers, but chitin and cellulose contain \( \beta \) form.

Step 3: Determine the Correct Option

Since amylase can only break down polysaccharides with glucose monomers in the \( \alpha \) form, the correct option is \text{(A) glycogen, starch, and amylopectin}.

Key Concepts

Glycosidic Linkage

Glycosidic linkages are the bonds that connect sugar molecules (monosaccharides) to form larger carbohydrate structures like polysaccharides. These linkages occur between the hydroxyl groups of two monosaccharides. The type of glycosidic linkage formed can affect the properties and digestibility of the resulting carbohydrate.

A glycosidic linkage can be in either the \(\alpha\) form or the \(\beta\) form, depending on the position of the hydroxyl group attached to the anomeric carbon (Carbon 1).

• \(\alpha\)-glycosidic linkage: The hydroxyl group on the anomeric carbon is in the opposite direction (trans) to the CH2OH side group. These linkages are digestible by enzymes like amylase.
• \(\beta\)-glycosidic linkage: The hydroxyl group on the anomeric carbon is in the same direction (cis) as the CH2OH side group. These linkages are usually not digestible by enzymes like amylase.

Understanding these distinctions helps in determining which carbohydrates can be broken down by certain enzymes, such as amylase.

Glucose Monomers

Glucose monomers are the building blocks of many important carbohydrates. Each glucose monomer is a simple sugar molecule with the chemical formula C6H12O6.

Monomers join together through glycosidic linkages to form disaccharides, oligosaccharides, and polysaccharides. These links can be categorized based on the position of the glucose units:

• \(\alpha\) form: Glucose units are linked by \(\alpha\)-glycosidic bonds.
• \(\beta\) form: Glucose units are linked by \(\beta\)-glycosidic bonds.

For example, in starch, glucose monomers are linked by \(\alpha 1,4\)-glycosidic bonds, making it digestible by amylase. On the other hand, cellulose consists of glucose monomers linked by \(\beta 1,4\)-glycosidic bonds, which most humans cannot digest.

Polysaccharides

Polysaccharides are large carbohydrate molecules composed of long chains of monosaccharide units bound together by glycosidic linkages. They can serve different functions in living organisms, such as energy storage or structural support.

Examples of polysaccharides include:

• Glycogen: A highly branched polysaccharide used by animals for energy storage. It contains glucose monomers in \(\alpha 1,4\)-glycosidic linkages with branches at \(\alpha 1,6\) points.
• Starch: A plant polysaccharide also used for energy storage, consisting of amylose and amylopectin. Both components have glucose monomers linked mostly in the \(\alpha 1,4\) form, making them digestible by amylase.
• Cellulose: A structural polysaccharide in plants. Its glucose monomers are linked by \(\beta 1,4\)-glycosidic bonds, making it indigestible for many animals, including humans.

The specific types of glycosidic linkages in these polysaccharides determine whether or not they can be broken down by amylase. For instance, only those with \(\alpha\)-glycosidic linkages, like glycogen and starch, can be digested by this enzyme.