How can a transcription factor increase transcription?

It binds near the promoter and helps RNA polymerase to bind, so more mRNA is made.

How does a repressor reduce gene expression?

It binds to DNA and blocks RNA polymerase from binding or moving along.

What is a primary transcript?

The pre-mRNA copy of a gene, containing both introns and exons.

What is RNA splicing?

Removal of introns from the primary transcript and joining of the exons to make mature mRNA.

What is alternative splicing?

Joining different combinations of exons so that one gene gives different mature mRNAs and proteins.

What is an epigenetic modification?

A change to gene expression that does not alter the DNA base sequence.

What does DNA methylation do?

Methyl groups on cytosine in the promoter stop transcription factors and RNA polymerase binding, silencing the gene.

How does histone acetylation affect transcription?

It loosens the chromatin so DNA is accessible and genes can be transcribed.

How does histone deacetylation affect transcription?

It makes histones bind DNA more tightly, so the chromatin is condensed and the gene is silenced.

How can non-coding RNA affect gene expression?

It can bind to DNA or mRNA, or recruit enzymes, to silence a gene or break down mRNA.

Why do cells with the same genome have different functions?

Different genes are expressed because of different transcription factors and epigenetic modifications.

Why are epigenetic patterns kept when a cell divides?

They are copied to daughter cells, so differentiated cells stay specialised.

Factors affecting gene expressionEdexcel A-Level Biology B: Flashcards

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What is a transcription factor?

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What is a transcription factor?: A protein that binds to specific DNA sequences and regulates transcription of a gene.
How can a transcription factor increase transcription?: It binds near the promoter and helps RNA polymerase to bind, so more mRNA is made.
How does a repressor reduce gene expression?: It binds to DNA and blocks RNA polymerase from binding or moving along.
What is a primary transcript?: The pre-mRNA copy of a gene, containing both introns and exons.
What is RNA splicing?: Removal of introns from the primary transcript and joining of the exons to make mature mRNA.
What is alternative splicing?: Joining different combinations of exons so that one gene gives different mature mRNAs and proteins.
What is an epigenetic modification?: A change to gene expression that does not alter the DNA base sequence.
What does DNA methylation do?: Methyl groups on cytosine in the promoter stop transcription factors and RNA polymerase binding, silencing the gene.
How does histone acetylation affect transcription?: It loosens the chromatin so DNA is accessible and genes can be transcribed.
How does histone deacetylation affect transcription?: It makes histones bind DNA more tightly, so the chromatin is condensed and the gene is silenced.
How can non-coding RNA affect gene expression?: It can bind to DNA or mRNA, or recruit enzymes, to silence a gene or break down mRNA.
Why do cells with the same genome have different functions?: Different genes are expressed because of different transcription factors and epigenetic modifications.
Why are epigenetic patterns kept when a cell divides?: They are copied to daughter cells, so differentiated cells stay specialised.

Exam questions on Factors affecting gene expression

A researcher studies a gene in liver cells that is transcribed only when a protein, factor F, enters the nucleus and binds to a DNA sequence next to the gene. In muscle cells factor F is absent and the gene is not transcribed, although muscle cells contain the same gene.
Explain how factor F can increase the rate of transcription of the gene in liver cells.2 marks
The gene for a muscle protein is transcribed in two different tissues. In both tissues the primary transcript has six exons. In tissue 1 the mature mRNA contains exons 1 to 6. In tissue 2 the mature mRNA contains exons 1, 2, 4, 5 and 6, and the protein it codes for is shorter and has a different function.
Explain why the two mRNA molecules lead to proteins with different functions.2 marks
Cells from a tumour show that the promoter region of a tumour suppressor gene has many methyl groups attached to its cytosine bases, and the histones around the gene have had their acetyl groups removed. The tumour suppressor gene is not expressed in these cells.
Explain how these modifications prevent expression of the tumour suppressor gene.3 marks

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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).