In the DNA (deoxyribonucleic acid) molecule, which specific sugar is found in the sugar–phosphate backbone?

Introduction / Context:
DNA and RNA are nucleic acids that store and transmit genetic information. They are both polymers made up of nucleotides, and each nucleotide contains a sugar component. The type of sugar present in the nucleotide helps distinguish DNA from RNA and influences the molecule's stability and function. This question asks you to identify the specific sugar present in the sugar–phosphate backbone of DNA.

Given Data / Assumptions:

The molecule in question is DNA, short for deoxyribonucleic acid. We are focusing on the sugar component of its backbone. Options include ribose, deoxyribose, pentose in general, sucrose and glucose. We assume basic knowledge of the structural differences between DNA and RNA.

Concept / Approach:
The sugar in DNA is deoxyribose, a five carbon (pentose) sugar that lacks one oxygen atom at the 2' carbon compared to ribose. In RNA, the corresponding sugar is ribose, which has a hydroxyl group at the 2' position. The absence of this hydroxyl group in deoxyribose makes DNA more chemically stable, which is one reason DNA is used as long term genetic storage in most organisms. Sucrose and glucose are not components of nucleic acid backbones; they are common dietary sugars and energy sources rather than structural sugars in DNA.

Step-by-Step Solution:
Step 1: Recall the full name of DNA: deoxyribonucleic acid, which already hints at deoxyribose as the sugar. Step 2: Remember that RNA stands for ribonucleic acid and contains ribose instead. Step 3: Recognise that both DNA and RNA sugars are pentose sugars, but the question asks for the specific sugar, not just the type. Step 4: Eliminate sucrose and glucose because they are not used as the sugar in the nucleic acid backbone. Step 5: Identify deoxyribose as the sugar found in DNA's sugar–phosphate backbone.

Verification / Alternative check:
Textbook diagrams of DNA nucleotides clearly label the sugar as deoxyribose, often showing the missing oxygen atom at the 2' position compared with ribose. Similarly, when tables compare DNA and RNA, one of the first differences listed is that DNA contains deoxyribose while RNA contains ribose. Matching these diagrams and descriptions to the options confirms deoxyribose as the correct answer.

Why Other Options Are Wrong:
Ribose is the sugar found in RNA, not DNA. Saying any pentose sugar at random ignores the specific structural requirement of DNA and is scientifically incorrect. Sucrose is a disaccharide composed of glucose and fructose and is a common table sugar, not a nucleic acid component. Glucose is a hexose sugar used in energy metabolism and polymerised into starch and glycogen, not used in the DNA backbone. These options do not accurately describe the sugar in DNA.

Common Pitfalls:
A common trap is to confuse the sugars of DNA and RNA because their names appear similar. Another pitfall is to overlook the word deoxy and think only about ribose as a general sugar. To avoid these errors, use the simple association: DNA equals deoxyribose, RNA equals ribose. Remembering this pairing makes it easy to answer questions about nucleic acid sugars, even under exam pressure.

Final Answer:
The sugar found in the sugar–phosphate backbone of DNA is deoxyribose.