Problem 20 - Objective Biology for NEET

Question

In glycogen, which kind of linkage is found between adjacent glucose molecule? (a) 1,4 (b) 1,6 (c) both (d) 1,2

Step-by-Step Solution

Answer

The type of linkage found between adjacent glucose molecules in glycogen is both α(1→4) and α(1→6), so the answer is (c) both.

Step 1: Understand Glycogen Structure

Glycogen is a polysaccharide that consists of glucose units. It is the energy storage molecule in animals and fungi. Similar to starch, the glucose units in glycogen are linked by glycosidic bonds.

Step 2: Identify Types of Linkages in Glycogen

There are two types of glycosidic linkages present in glycogen, α(1→4) and α(1→6). The α(1→4) linkages form the linear chain while α(1→6) linkages create branches.

Step 3: Match the Given Options

Given the identification of both α(1→4) and α(1→6) linkages in glycogen, the correct answer aligns with option (c) both.

Key Concepts

Glycosidic Linkages

Understanding glycosidic linkages is fundamental when studying the structure of glycogen. These chemical bonds are what link individual glucose units together in polysaccharides, which include starch, cellulose, and glycogen. There are two types of glycosidic bonds in glycogen - α(1→4) and α(1→6). The α(1→4) linkages are the more common ones, and they form the long, straight chains of glucose molecules. Imagine these chains as a train with many cars connected end-to-end; these are the glucose units held together by α(1→4) glycosidic linkages.

Meanwhile, the α(1→6) linkages are responsible for branching out from the straight chains. These branches make glycogen a highly compact and branched molecule, allowing it to store abundant energy in a small space. When the body needs glucose for energy, enzymes break these glycosidic bonds to release glucose. This process ensures a steady supply of glucose to cells when needed, especially in between meals or during physical activity.

Polysaccharides

Moving on to polysaccharides, they are complex carbohydrates, essentially long chains of monosaccharides linked together. Polysaccharides serve various functions in living organisms, from structural components to energy storage. In humans and other animals, glycogen plays the critical role of storing glucose, which cells can later break down to produce energy. This makes glycogen an essential polysaccharide for energy metabolism.

Polysaccharides are classified based on their structure and purpose. For instance, cellulose is a structural polysaccharide in plants, providing rigidity to cell walls, whereas glycogen is a storage polysaccharide in animals. The structure of a polysaccharide determines its properties and its function in living organisms. For example, the branched nature of glycogen allows for the rapid mobilization of glucose when needed, something straight-chain polysaccharides like cellulose cannot do because of their structural function.

Glucose Units

At their most basic, glucose units are the building blocks of polysaccharides like glycogen. Each glucose unit is a molecule of sugar that represents the simplest form of carbohydrate energy readily accessible to the body. In glycogen, glucose units are strung together in a particular fashion that optimizes for space and efficiency of energy storage.

Thinking about these glucose units in terms of numbers, they are akin to beads on a string; where each 'bead' is a potential energy source that can be used when necessary. When glycogen is synthesized in the body through a process called glycogenesis, glucose molecules are added to the growing glycogen chain using energy from ATP molecules. The structure of glycogen, with its α(1→4) and α(1→6) glycosidic linkages, is an evolutionary adaptation designed to meet the rapid energy-release requirements of animals, including humans during high-energy-demand situations.