Problem 20 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

Which of the following statement is not correct? [Main Online April 25, 2013] (a) Amylopectin is a branched polymer of \(\alpha\)-glucose. (b) Cellulose is a linear polymer of \(\beta\)-glucose (c) Glycogen is the food reserve of plants (d) All proteins are polymers of \(\alpha\)-amino acids.

Step-by-Step Solution

Answer

Statement (c) is not correct.

Step 1: Analyze Statement (a)

Evaluate whether "Amylopectin is a branched polymer of \(\alpha\)-glucose" is correct. Amylopectin is part of starch, which is indeed a branched polymer of \(\alpha\)-glucose units. Therefore, statement (a) is correct.

Step 2: Analyze Statement (b)

Evaluate whether "Cellulose is a linear polymer of \(\beta\)-glucose" is correct. Cellulose is a natural polymer consisting of a linear chain of hundreds to thousands of \(\beta\)-glucose units. Thus, statement (b) is correct.

Step 3: Analyze Statement (c)

Examine the statement "Glycogen is the food reserve of plants." Glycogen is actually the primary storage form of glucose in animals and humans, not plants. Plants store glucose in the form of starch. Hence, statement (c) is not correct.

Step 4: Analyze Statement (d)

Evaluate whether "All proteins are polymers of \(\alpha\)-amino acids" is correct. Proteins are indeed polymers made up of \(\alpha\)-amino acids, linked through peptide bonds. Therefore, statement (d) is correct.

Key Concepts

Amylopectin

Amylopectin is a complex carbohydrate and a crucial ingredient of starch. It consists of

• branched chains
• made up of \(\alpha\)-glucose units

that are linked together. Unlike amylose, another starch component which is linear, amylopectin has many branching points. These branches occur every

• 24 to 30 glucose units

and provide a structure similar to a tree. Due to this structure,

• enzymes can quickly digest amylopectin
• making it an efficient energy source

for humans and animals. You can find amylopectin in foods like potatoes, vegetables, and cereals.
Its branched structure contributes to the gelatinization properties in cooking and adds a thickening ability to sauces and gravies.

Cellulose

Cellulose is a vital structural component of the cell wall in plants. It is an unbranched polymer consisting of

• repeating \(\beta\)-glucose units

in a straight chain. Due to the \(\beta\) configuration of the glucose molecules, cellulose has a very stable and rigid structure.This sturdy build gives plants their strength and toughness.
Humans, however, cannot digest cellulose because they lack the necessary enzymes to break the

• \(\beta\)-glycosidic bonds

in cellulose. Instead, cellulose serves

• as dietary fiber

which helps maintain a healthy digestive system.

• Ruminants like cows can digest cellulose due to specialized bacteria in their stomachs.

Additionally, cellulose is used in producing goods like paper, cotton, and even biofuels.

Glycogen

Glycogen acts as the primary glucose storage form in animals and humans. This complex carb resembles amylopectin with its branched structure, but is even more densely branched. Its more frequent branching occurs every

• 8 to 12 glucose units

aver the amylopectin structure. Glycogen plays a critical role in energy regulation. When you exercise or need a quick form of energy, glycogen is broken down into glucose.
It is mostly stored in

• the liver and skeletal muscles

where it serves different functions:

• In the liver, glycogen helps maintain blood sugar levels.
• In muscles, it serves as a quick energy source during physical activity.

This storage system is an essential part of energy management in the body, essentially functioning as a fuel reserve that can be tapped into when needed.

Proteins

Proteins are complex molecules that play a crucial role in nearly all biological processes. They are polymers made up of \(\alpha\)-amino acidslinked by peptide bonds. There are

• twenty different amino acids

that can combine in a multitude of ways to create the proteins needed for various functions. Each combination forms a unique protein, determining its shape and function.
Proteins are involved in:

• building tissues and muscles
• acting as enzymes to speed up chemical reactions
• supporting immune functions
• transporting molecules

The sequence of amino acids in a protein dictates its 3D structure, which is essential for its specific biological activity. Therefore, understanding the composition and function of proteins is key to exploring biology and medicine.