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A1.2.7—Differences between DNA and RNA

DNA and RNA differ in sugar, bases, strand structure, and usual length, giving each nucleic acid distinct roles in cells.

Syllabus
First assessment 2025
Objective
A1.2.7
Level
HL

Exam analysis

Chance of appearing4%of analysed past papers
Latest appearanceMay 2025
Most common paperPaper1
Typical marks1–3

Common command terms

  • Identify
  • State
  • Distinguish
  • Determine

Scoring notes

Common mistake
Listing a DNA feature as an RNA feature, especially thymine, uracil, ribose, or deoxyribose.

Recent exam appearances

May 2025Paper2 HL · TZ33(a)[ 1 ]A1.2.7—Differences between DNA and RNA
May 2019Paper2 HL · TZ27(a)[ 3 ]A1.2.7—Differences between DNA and RNA
May 2019Paper1 HL · TZ17[ 1 ]A1.2.7—Differences between DNA and RNA
May 2016Paper1 HL · TZ05[ 1 ]A1.2.7—Differences between DNA and RNA
Practice this objective

Coverage 2016–2025 · Updated 14 Jul 2026

DNA and RNA Differ in Three Useful Ways

DNA and RNA differ in sugar, one base and usual strand structure, and those differences fit their different cellular roles.

DNA uses deoxyribose and thymine and is usually double-stranded, making a stable long-term store. RNA uses ribose and uracil and is usually single-stranded, making temporary messages and folded functional molecules practical.

Compare the molecules:

  • sugar: deoxyribose / ribose
  • base: thymine / uracil
  • usual form: double-stranded / single-stranded

A cell can transcribe a DNA sequence into RNA: the RNA copy uses uracil and can leave the nucleus while the DNA template remains protected.

‘RNA is always single-stranded’ is a usual structural description, not a rule that forbids every paired region.

Differences between DNA and RNA

Assessment in practice

1–2 marks
How it is assessed

This objective is assessed through structured response, commonly using Identify / State / Distinguish.

Command terms

Identify / State / Distinguish / Determine

What earns marks

Build the answer around this relationship: Differences between DNA and RNA should be described using precise molecular vocabulary.

Watch for

Listing a DNA feature as an RNA feature, especially thymine, uracil, ribose, or deoxyribose.

Representative question

Question 1

[Maximum number: 3]

Distinguish between the structures of DNA and RNA.

Retrieve The Core Rules

The core chain is: nucleotides have three parts; condensation builds the sugar-phosphate backbone; base order stores information; complementary pairing lets DNA copy and express that information.

  • Nucleotide parts: phosphate, pentose sugar, nitrogenous base.
  • Polymer rule: condensation forms a sugar-phosphate backbone.
  • Code rule: base order stores information and triplet codons specify amino acids.
  • Pairing rule: A-T or A-U, and C-G, enables replication and gene expression.
  • DNA/RNA contrast: DNA uses deoxyribose/T and is usually double-stranded; RNA uses ribose/U and is usually single-stranded.

Concept essentials

  • Differences between DNA and RNA should be described using precise molecular vocabulary.
  • Structure and information must be kept separate: backbones provide continuity while bases carry sequence meaning.
  • Exam answers should match the command term and avoid adding unsupported extra claims.