DNA (deoxyribonucleic acid) is a large polymer made up of repeating structural units known as what?

Introduction / Context:
DNA is the hereditary material in almost all living organisms and is often described as a long chain like molecule or polymer. Polymers are made of many smaller repeating units linked together. Understanding what these repeating units are called in the context of DNA is fundamental to molecular biology. This question asks you to identify the proper term for these basic building blocks.

Given Data / Assumptions:

• We are considering the structure of DNA as a polymer.
• Options include nucleotides, ribosomes, peptides, amino acids, and monosaccharides.
• We assume basic knowledge of macromolecules such as nucleic acids, proteins, and carbohydrates.
• The question focuses on the repeating units that form the DNA strand itself.

Concept / Approach:
DNA is a nucleic acid composed of chains of nucleotides. Each nucleotide consists of three parts: a nitrogenous base (adenine, thymine, cytosine, or guanine), a five carbon sugar (deoxyribose), and a phosphate group. These nucleotides are linked together by phosphodiester bonds to form long strands. Ribosomes are cellular structures involved in protein synthesis, peptides and amino acids are associated with proteins, and monosaccharides are sugar units that form carbohydrates. Only nucleotides are the repeating units specific to nucleic acids like DNA and RNA.

Step-by-Step Solution:
Step 1: Recall that DNA stands for deoxyribonucleic acid, indicating that it is a nucleic acid. Step 2: Remember that nucleic acids are polymers of smaller units called nucleotides. Step 3: Identify a nucleotide as being composed of a sugar, a phosphate group, and a nitrogenous base. Step 4: Recognise that ribosomes are organelles, not subunits of DNA; they are composed of rRNA and proteins. Step 5: Understand that peptides and amino acids are building blocks of proteins, not nucleic acids. Step 6: Note that monosaccharides are units of carbohydrates like starch or cellulose, not DNA. Step 7: Therefore, the repeating units of DNA are correctly called nucleotides.

Verification / Alternative check:
Biochemistry texts depict DNA as a double helix with two antiparallel chains of nucleotides. They show each nucleotide as a base attached to deoxyribose with a phosphate group linking the sugars together. The term "polynucleotide chain" is frequently used to describe DNA strands, confirming that nucleotides are the repeating units. In contrast, discussions of protein structure emphasise amino acids as building blocks, clearly separating the terminology for different macromolecules.

Why Other Options Are Wrong:
Ribosomes: Complex cellular structures that build proteins; they are not the units forming DNA. Peptides: Short chains of amino acids; they belong to protein structure, not DNA. Amino acids: The monomeric units of proteins, not of DNA or RNA. Monosaccharides: Single sugar molecules like glucose and fructose, which form carbohydrates, not nucleic acids.

Common Pitfalls:
Students sometimes confuse biochemical terms because all macromolecules are polymers. A simple way to remember is: nucleic acids are made of nucleotides, proteins are made of amino acids, and carbohydrates are made of monosaccharides. Keeping these associations clear helps avoid mixing up nucleotides and amino acids in exam questions.

Final Answer:
The repeating structural units that make up DNA are called nucleotides.