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D1.2.13 (HL)—Initiation of transcription at promoter

Promoters are upstream non-coding DNA regions that position RNA polymerase and help initiate regulated transcription of a gene in cells.

Syllabus
First assessment 2025
Objective
D1.2.13
Level
HL

Exam analysis

Chance of appearing1%of analysed past papers
Latest appearanceMay 2024
Most common paperPaper2
Typical marks2

Common command terms

  • Explain

Recent exam appearances

May 2024Paper2 ["HL"] · TZ14(c)[ 2 ]D1.2.13 (HL)—Initiation of transcription at promoter

Coverage 2024–2024 · Updated 16 Jul 2026

Promoters and Transcription Factors Assemble the Start Complex

HL only

A promoter is a DNA region that positions the transcription machinery near a gene's transcription start site. General transcription factors bind first and help recruit RNA polymerase.

Regulatory input Binding relationship Typical effect on initiation
activator transcription factor binds a regulatory DNA sequence such as an enhancer stabilizes or recruits the initiation machinery
repressor transcription factor binds a regulatory sequence or interferes with the complex reduces assembly or activity of the initiation machinery

Regulatory DNA may be far from the promoter in the linear sequence. DNA looping can bring bound factors into contact with promoter-associated proteins.

The combined transcription-factor state changes how often RNA polymerase initiates, altering the amount of pre-mRNA produced from the gene.

Control Protein Output at Several Checkpoints

HL only
Checkpoint What can change Consequence for protein output
transcription initiation promoter and transcription-factor activity amount of pre-mRNA made
RNA processing cap, tail and exon combination mRNA stability, export and encoded sequence
translation initiation successful AUG recognition and ribosome assembly whether and where translation begins
post-translational processing folding, cleavage, modification and assembly protein activity or location
proteasomal degradation ubiquitin tagging and breakdown rate protein lifetime and abundance

Across these checkpoints, sequence direction stays consistent: RNA is made 5′→3′, the ribosome reads mRNA 5′→3′ and the polypeptide grows from N-terminus to C-terminus.

Gene expression is therefore not a single on/off event. A cell controls which message is made, how it is processed, whether it is translated, how the product is activated and how long the protein remains.

Initiation of transcription at promoter

HL only

[ 2 ]

Explain the function of a promoter in DNA.

Concept essentials

  • Promoters are non-coding DNA sequences linked to transcription start sites.
  • RNA polymerase or transcription factors bind at promoter regions.
  • Promoters help determine where transcription begins.
  • Promoter activity contributes to regulation of gene expression.