D1.2.14 (HL)—Non-coding sequences in DNA
Non-coding DNA includes sequences that regulate genes, protect chromosome ends or code for functional RNA rather than polypeptides in genomes.
- Syllabus
- First assessment 2025
- Objective
- D1.2.14
- Level
- HL
Exam analysis
Chance of appearing10%of analysed past papers
Latest appearanceNovember 2024
Most common paperPaper1
Typical marks1
Common command terms
- State
Scoring notes
- Common mistake
- Equating non-coding DNA with having no function.
Recent exam appearances
November 2024Paper1 ["HL"] · TZ027[ 1 ]D1.2.14 (HL)—Non-coding sequences in DNA
November 2022Paper2 ["HL"] · TZ04(c)(ii)[ 1 ]D1.2.14 (HL)—Non-coding sequences in DNA
May 2021Paper1 ["HL"] · TZ126[ 1 ]D1.2.14 (HL)—Non-coding sequences in DNA
May 2019Paper2 ["HL"] · TZ22(a)(iii)[ 2 ]D1.2.14 (HL)—Non-coding sequences in DNA
May 2019Paper1 ["HL"] · TZ214[ 1 ]D1.2.14 (HL)—Non-coding sequences in DNA
Practice this objective
Coverage 2013–2024 · Updated 16 Jul 2026
Non-Coding DNA Can Regulate the Genome
HL onlyNon-coding DNA does not code for polypeptide sequence, but it can have regulatory, processing, structural or functional-RNA roles.
| Required eukaryotic example | Why it is non-coding |
|---|---|
| Regulators of gene expression | Control when/how strongly genes are transcribed |
| Introns | Transcribed into pre-mRNA but removed before translation |
| Telomeres | Repetitive chromosome-end DNA with a protective structural role |
| Genes for rRNA and tRNA | Produce functional RNAs rather than polypeptides |
A tRNA gene is transcribed to a functional tRNA molecule; its RNA product participates in translation but is not itself translated.
Non-coding does not mean non-functional or never transcribed. Limit examples here to the four syllabus categories.
Non-coding sequences in DNA
HL onlyAssessment in practice
1 marksHow it is assessed
This objective is assessed through structured response, commonly using State.
Command terms
State
What earns marks
Build the answer around this relationship: Non-coding DNA can regulate transcription.
Watch for
Equating non-coding DNA with having no function.
Representative question
Question 1
DNA has regions that do not code for proteins. State two functions of these regions.
1.
2.
HL Protein Synthesis Details
HL onlyRNA polymerase reads template DNA 3' to 5' and synthesizes RNA 5' to 3'; ribosomes translate mRNA codons in the 5' to 3' direction. Promoters mark transcription start regions and orientation; transcription factors help RNA polymerase bind and initiate in eukaryotes. Non-coding DNA does not code for polypeptide amino acid sequences and includes introns, regulatory sequences, telomeres, rRNA genes, and tRNA genes. Eukaryotic pre-mRNA is modified before export and translation by adding a 5' cap and poly-A tail and removing introns by splicing. Alternative splicing joins different exon combinations from one pre-mRNA, so one gene can produce multiple protein variants in different cells or stages. Translation initiation assembles ribosomal subunits at the start codon AUG; initiator tRNA enters the P site and A, P, and E sites organize tRNA movement. Newly made polypeptides may be folded, cleaved, or chemically modified; preproinsulin processing to active insulin is a key example. Proteasomes degrade tagged, damaged, or unneeded proteins; amino acid recycling supports new protein synthesis and proteome quality control.
Concept essentials
- Non-coding DNA can regulate transcription.
- Telomeres protect the ends of chromosomes.
- Some DNA sequences code for functional RNAs such as tRNA or rRNA.
- Introns are removed from eukaryotic RNA before mature mRNA is translated.