A molecule of DNA is a polymer composed of which type of repeating subunit?

Introduction / Context:
Deoxyribonucleic acid, or DNA, is the hereditary material in almost all living organisms. At a molecular level, DNA is built as a long chain, or polymer, of smaller repeating units. This question checks whether you know the correct name for those basic building blocks and can distinguish them from higher level structures and other biomolecules.

Given Data / Assumptions:

• The question asks about the repeating subunit in a DNA molecule.
• The options include amines, nucleotides, chromosomes, and fatty acids.
• We assume familiarity with basic biomolecules such as proteins, lipids, and nucleic acids.

Concept / Approach:
DNA is a nucleic acid, and nucleic acids are polymers made up of nucleotide monomers. Each nucleotide consists of three parts: a phosphate group, a five carbon sugar (deoxyribose in DNA), and a nitrogenous base. Chromosomes are higher order structures composed of DNA and associated proteins, not the repeating units themselves. Fatty acids and most amines belong to other classes of molecules, not to nucleic acid monomers. Therefore, to answer this question, we need to identify which option correctly names the monomer of DNA.

Step-by-Step Solution:
Step 1: Consider option A, amines. Amines are organic molecules derived from ammonia and appear in many biomolecules, but they are not the standard name for DNA monomers.Step 2: Consider option B, nucleotides. Textbooks describe DNA as a polymer of nucleotides linked by phosphodiester bonds, so this matches the known structure.Step 3: Consider option C, chromosomes. A chromosome is a long DNA molecule packaged with proteins, representing a higher organizational level, not the basic repeating subunit.Step 4: Consider option D, fatty acids. Fatty acids are components of lipids and membranes, not of DNA.Step 5: Conclude that nucleotides are the correct repeating subunits of DNA, making option B correct.

Verification / Alternative check:
You can verify the answer by recalling that the structure of DNA is often illustrated as a ladder or double helix where each rung corresponds to a pair of nitrogenous bases from two nucleotides, and the sides are sugar phosphate backbones built from linked nucleotides. The term nucleotide is consistently used in genetics and molecular biology to describe the monomer units of both DNA and RNA.

Why Other Options Are Wrong:
Option A is wrong because amines refer broadly to nitrogen containing organic compounds and not specifically to DNA monomers. Option C is wrong because chromosomes are made of DNA and proteins and represent entire structures rather than monomer units. Option D is wrong because fatty acids belong to lipids and play structural and energy storage roles, not genetic information storage.

Common Pitfalls:
A common mistake is to confuse levels of biological organization, for example mixing up nucleotides, genes, DNA molecules, and chromosomes. Another pitfall is to associate any nitrogen containing molecule, such as an amine, with DNA without recognizing the precise terminology used in molecular biology. Learning to distinguish between monomers, polymers, and higher order structures helps avoid such confusion in exam questions.

Final Answer:
Nucleotides.