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Gene Control- Transcription Factors — Cambridge AS & A Level Biology 9700 Revision Notes & Topical Questions

5 min read 9 parts Lesson 17 of 18 1 quiz

📚 Cambridge AS & A Level Biology 9700 Hub / Topical Revision
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16.3.3 Gene Control: Transcription Factors — CAMBRIDGE AS & A LEVEL BIOLOGY 9700 — REVISION NOTES notes: Explain how transcription factors regulate gene expression, including gibberellin, DELLA and PIF.Prokaryotes — use operons.Eukaryotes — also use transcription factors.Definiti…

  • Definition
  • Environment
  • Promoter binding
  • Amylase gene
  • Gibberellin receptor and enzyme
  • Observation

Part 1 of 7Gene control in eukaryotes

Prokaryotes
  • Prokaryotes use operons.
Eukaryotes
  • Eukaryotes also use transcription factors.
Definition
  • Definition a transcription factor is a protein that controls transcription of genes by binding to a specific region of DNA.
Role
  • Role ensures genes are expressed in the correct cells, at the correct time and to the right level.
Number
  • Number about 10 % of human genes code for transcription factors.
Environment
  • Environment allow organisms to respond to their environment.

Part 2 of 7How transcription factors work

Promoter binding
  • Promoter binding some bind the promoter region of a gene.
Effect
  • Effect binding can allow or prevent transcription.
Rate
  • Rate the transcription factor increases or decreases the rate of transcription.
Hormones
  • Hormones some hormones act through transcription factors.
PIF
  • PIF a plant transcription factor that activates transcription of the amylase gene.

Part 3 of 7Gibberellin and amylase

Gibberellin
  • Gibberellin hormone in plants such as wheat and barley that controls seed germination.
Effect
  • Effect stimulates synthesis of amylase by influencing transcription of the amylase gene.
Evidence
  • Evidence gibberellin applied to a germinating seed increases the amount of amylase mRNA.

Part 4 of 7Components of the mechanism

Components of the mechanism
DELLA
  • DELLA a repressor protein.
PIF
  • PIF a transcription factor.
Promoter
  • Promoter of the amylase gene.
Amylase gene
  • Amylase gene the gene being expressed.
Gibberellin receptor and enzyme
  • Gibberellin receptor and enzyme bind gibberellin.

Part 5 of 7Steps of the mechanism

1
DELLA protein is bound to PIF, preventing PIF binding the promoter of the amylase gene.
2
No transcription occurs.
3
Gibberellin binds a gibberellin receptor and enzyme, which starts the breakdown of DELLA.
4
PIF is released and binds to the promoter.
5
Transcription of the amylase gene begins.
6
Amylase is produced.

Part 6 of 7RNA analysis

Observation
  • Observation most cells look almost identical and have the same DNA.
Difference
  • Difference they express different genes.
Method
  • RNA made by transcription can be analysed.
Conclusion
  • Conclusion matching RNA to genes shows which genes are expressed in a particular cell.

Part 7 of 7More from the specification

More from the specification
Lac Operon Repression Without Lactose
  • In the bacterium Escherichia coli,
  • when lactose is not present, a lac repressor protein bound to the operator region physically blocks RNA polymerase from transcribing the downstream structural genes.
Lac Operon Induction With Lactose
  • When lactose is present in the growth medium, allolactose binds to the allosteric site of the repressor protein, altering its conformation so it detaches from the operator,
  • allowing RNA polymerase to initiate transcription.
Enzymatic Roles of Structural Genes
  • The lac operon structural gene lacZ codes for beta-galactosidase (lactase),
  • which hydrolyses lactose into glucose and galactose to provide cellular energy,
  • while lacY codes for lactose permease to facilitate sugar transport.
Transcription Factors and Eukaryotic Gene Control
  • In eukaryotic cells, transcription factors bind to specific promoter or enhancer DNA sequences to recruit RNA polymerase and regulate whether gene transcription takes place in response to environmental or hormonal cues.
Inducible enzyme
  • Enzyme made when its substrate is present.
Lactose
  • A disaccharide of glucose and galactose.
Operator
  • Region where the repressor binds.
Lactase
  • An enzyme that breaks lactose into glucose and galactose.
Bacterium
  • A single-celled organism with no nucleus.
Substrate
  • The molecule that an enzyme acts on and which binds to the active site.
Structural gene
  • Gene coding for a functional protein.
Repressible enzyme
  • Enzyme whose synthesis is stopped by a repressor.
Effector molecule
  • Molecule that binds and changes a regulatory protein.

Key terms

TermMeaning
Transcription factorProtein controlling transcription by binding DNA.
PIFTranscription factor activating the amylase gene.
DELLA proteinRepressor that binds PIF.
PromoterDNA region where transcription begins.
GibberellinPlant hormone that triggers breakdown of DELLA.
Gene expressionUse of a gene to make a protein.

Avoid these mistakes

1
Saying gibberellin binds DNA directly — it acts through its receptor, DELLA and PIF.
2
Saying DELLA activates transcription — it blocks PIF.
3
Saying all cells have different DNA — they have the same DNA and express different genes.
4
Saying transcription factors are made only in plants — eukaryotes in general use them.

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