Question

Which is not a homopolymer?

• A. Insulin
• B. Chitin
• C. Glycogen
• D. Collagen

Hint:

Remember that proteins (like Insulin and Collagen) are polymers built from various types of amino acids, making them heteropolymers. Polysaccharides composed of a single repeating monosaccharide unit (like glucose in glycogen or N-acetylglucosamine in chitin) are homopolymers.

Answer 1

The Correct Option is D

Step 1: Define homopolymer and heteropolymer.

A homopolymer is a polymer formed from a single, identical type of monomer unit.
A heteropolymer (or copolymer) is a polymer formed from two or more different types of monomer units. Step 2: Analyze the monomer units of each given option and classify them.
(A) Insulin: Insulin is a protein hormone. Proteins are polymers made up of amino acid monomers. The functional insulin molecule (composed of A and B chains) contains a sequence of many different types of amino acids. Therefore, by definition, insulin is a heteropolymer.
(B) Chitin: Chitin is a complex polysaccharide that forms the exoskeletons of arthropods and cell walls of fungi. It is a linear polymer composed exclusively of repeating units of N-acetylglucosamine. Since it consists of only one type of monomer, chitin is a homopolymer.
(C) Glycogen: Glycogen is a branched polysaccharide that serves as the primary glucose storage molecule in animals and fungi. It is composed exclusively of repeating units of glucose. Since it consists of only one type of monomer, glycogen is a homopolymer.
(D) Collagen: Collagen is a major structural protein found in connective tissues. Like all proteins, it is composed of amino acids. While collagen's primary structure is characterized by highly repetitive sequences (e.g., Gly-X-Y, where X and Y are often proline or hydroxyproline, but can be other amino acids), it is still made from multiple different types of amino acids. Therefore, collagen is a heteropolymer. Step 3: Identify which option(s) are NOT homopolymers.
The question asks to identify the option that is \textit{not} a homopolymer, meaning we are looking for a heteropolymer. Based on our analysis:
Chitin (B) is a homopolymer.
Glycogen (C) is a homopolymer.
Insulin (A) is a heteropolymer (thus, not a homopolymer).
Collagen (D) is a heteropolymer (thus, not a homopolymer). Both Insulin and Collagen are heteropolymers. In a strictly defined context, both (A) and (D) are correct answers to the question "Which is not a homopolymer?". However, if this is a single-choice question and (D) is the designated correct answer, it implies that among the given choices, Collagen is the intended non-homopolymer.