A1.2 Nucleic acids
Explore how nucleotide components, bonding, base pairing and sequence give DNA and RNA their structures, information capacity, shared code and experimental significance.
- Syllabus
- First assessment 2025
- Topic
- A1.2
- Level
- SL
Exam analysis
Chance of appearing36%of analysed past papers
Latest appearanceNovember 2025
Most common paperPaper1
Typical marks1
Most tested objectives
Common question formats
- Diagram interpretation
- Definition or recall
- Structured response
- Data analysis
- Calculation
- Comparison
- Graph interpretation
Recent exam appearances
November 2025Paper2 SL · TZ32(c)[ 2 ]A1.2.7—Differences between DNA and RNA
November 2025Paper2 SL · TZ32(a)[ 2 ]A1.2.15 (HL)—Chargaff's data
May 2025Paper2 SL · TZ15(b)[ 2 ]A1.2.7—Differences between DNA and RNA
May 2025Paper1B SL · TZ14(c)[ 1 ]A1.2.13 (HL)—Structure of a nucleosome
May 2025Paper1A SL · TZ32[ 1 ]A1.2.9—Diversity of DNA base sequences
Practice this topic
Coverage 2010–2025 · Updated 14 Jul 2026
Objective notes
10 learning objectives• DNA is the genetic material of all living organisms
• DNA occurs in chromosomes and also in mitochondria and chloroplasts
• Some viruses use RNA, but viruses are not considered living organisms
• A nucleotide contains a phosphate group, pentose sugar, and nitrogenous base
• DNA nucleotides use deoxyribose; RNA nucleotides use ribose
• Bases include purines A/G and pyrimidines C/T/U
• Condensation reactions link nucleotides by sugar-phosphate bonds
• The sugar-phosphate backbone is a continuous covalent chain
• Bases project from the backbone and carry sequence information
• Genetic information lies in the order of nitrogenous bases
• DNA uses A, T, G, C; RNA uses A, U, G, C
• Triplet codons specify amino acids in protein synthesis
• RNA is a single-stranded polynucleotide formed by condensation
• RNA contains ribose and the bases A, U, G, and C
• mRNA, tRNA, and rRNA have different roles in protein synthesis
• DNA has two antiparallel polynucleotide strands in a double helix
• Complementary bases pair by hydrogen bonding: A-T and G-C
• Draw bases attached to sugars, not phosphates
• DNA is usually double-stranded; RNA is usually single-stranded
• DNA uses deoxyribose and thymine; RNA uses ribose and uracil
• RNA molecules are usually much shorter than DNA molecules
• A pairs with T in DNA and U in RNA; C pairs with G
• Complementary base pairing enables accurate DNA replication
• It also enables transcription and translation in gene expression
• DNA can vary in length and in base sequence
• Genome size and gene number vary widely between organisms
• Base-sequence diversity gives DNA enormous information-storage capacity
• The 64 codons have nearly the same meanings across life
• Conserved genes for transcription, translation, and ribosomes support common ancestry
• Synonymous mutations can preserve amino acid sequences