Question

Which of the following carbohydrates are branched polymer of glucose? (A) Amylose (B) Amylopectin (C) Cellulose (D) Glycogen

Short answer

(B) Amylopectin and (D) Glycogen are the correct answers, as both are branched polymers of glucose with α(1→4) glycosidic linkages (linear chain) and α(1→6) glycosidic linkages (branch points) between glucose units.

Step-by-step solution

Amylose

Amylose is a linear, unbranched polysaccharide composed of glucose units linked through α(1→4) glycosidic bonds. Since amylose is unbranched, it is not the correct answer.

Amylopectin

Amylopectin is a branched polysaccharide composed of glucose units. It has both α(1→4) glycosidic linkages (linear chain) and α(1→6) glycosidic linkages (branch points) between glucose units. Since amylopectin is branched, it could be the correct answer.

Cellulose

Cellulose is a linear, unbranched polysaccharide composed of glucose units linked through β(1→4) glycosidic bonds. Since cellulose is unbranched, it is not the correct answer.

Glycogen

Glycogen is a highly branched polysaccharide composed of glucose units. It has both α(1→4) glycosidic linkages (linear chain) and α(1→6) glycosidic linkages (branch points) between glucose units. Since glycogen is branched, it could also be the correct answer. Based on our analysis, both amylopectin and glycogen are branched polymers of glucose. Therefore, the correct answer is (B) Amylopectin and (D) Glycogen.

Key concepts

Amylopectin

Amylopectin is one of the two components of starch, and it's the reason why starch has a branched structure. It is a large, branched molecule made up of numerous glucose units. The key to its structure lies in the types of bonding between these glucose units.

Amylopectin contains α(1→4) glycosidic bonds, which are responsible for the linear chains of glucose. However, what makes it distinct are the α(1→6) glycosidic bonds, occurring at the branch points approximately every 24 to 30 glucose units. These special bonds create a tree-like structure, allowing enzymes easier access to the glucose molecules during digestion. This accessibility speeds up the energy release from amylopectin, an important feature for both plants and animals that store starch for energy.

Glycogen

Glycogen is often referred to as the animal equivalent of starch, it's an essential form of energy storage in humans and animals. Similar to amylopectin in plants, glycogen is a branched polymer of glucose. But unlike amylopectin, glycogen has a much higher branch density, with branches occurring every 8 to 12 glucose units.

This frequent branching allows for rapid release of glucose when energy is needed by the body, such as during physical activity. Glycogen is primarily stored in the liver and muscles, and enzymes break it down whenever there's a need to mobilize energy reserves. The highly branched structure of glycogen makes it soluble in water, which is crucial for its role in metabolic processes.

Carbohydrates Structure

Understanding the structure of carbohydrates is fundamental to comprehending how they serve various functions in living organisms. Carbohydrates are organic compounds made up of carbon, hydrogen, and oxygen atoms, usually with a hydrogen to oxygen atom ratio of 2:1.

The smallest units of carbohydrates are monosaccharides, such as glucose. These monosaccharides can link together in different ways to form disaccharides, oligosaccharides, and polysaccharides. The glycosidic bonds that link monosaccharides can differ in position and orientation, such as the α(1→4) bonds in starch and glycogen or the β(1→4) bonds in cellulose. These different linkages result in diverse structures and properties, leading to varying digestibility and function in the body.

Polysaccharides

Polysaccharides represent a group of complex carbohydrates that are formed by the linkage of multiple monosaccharides. These large macromolecules can serve various roles from structural components to energy storage. Common examples are starch in plants and glycogen in animals for energy, and cellulose in plants for structural support.

The structure of polysaccharides includes simple linear chains as well as highly branched complexes such as amylopectin and glycogen. The way in which the glucose units are bonded together in polysaccharides significantly affects their properties, including solubility, digestibility, and the speed at which they are metabolized. This complexity makes polysaccharides versatile biological materials that are essential to a number of physiological processes in living organisms.