Transcription factors Flashcards
What is a transcription factor?
Proteins that bind to DNA to regulate gene expression by changing the rate at which mRNA is produced.
Where to TF’s bind to?
They bind to a region next to the gene called a PROMOTER or another region called an ENHANCER
Explain how TF’s regulate gene expression
- Promoter regions allow the binding of RNA polymerase at the base of a gene to stimulate transcription.
- An enhancer regions makes the gene more accessible by loosening the binding to DNA HISTONE proteins in the chromatin, making chromatin more available to RNA polymerase, stimulating transcription.
OR
- Enhancer regions can also cause chromatin to tighten up so less gene expression is possible, inhibiting transcription.
Give examples of how TF control gene expression
Development - they organise gene activity in forming tissues/organs of an embryo
Horomonal control - cells affected by oestrogen have a receptor molecule which binds to a group of TF’s to activate specific genes.
Control of cell cycle - changes in a dividing cell and time of division
Pathogens controlling host cells - some bacteria produce TFs which modify gene expression in host nuclei.
How does RNA splicing produce different products from a specific gene ?
Post transcription modification of mRNA results in different products.
This is done by the removal of non coding regions of DNA - INTRONS.
SLICEOSOMES produce mature mRNA by joining exons together, producing different polypeptides from the same gene after translation.
What do epigenetics do?
They control how genes are expressed and affect the phenotype of a cell without affecting the DNA base sequence.
DNA methylation, histone modification and non coding RNA are examples of epigenetic control.
Explain DNA methylation.
A METHYL GROUP is added to cystosine in a DNA molecule, stopping transcription of a gene.
This SILENCES a gene and it isn’t expressed.
DNA demethylation causes the removal of a methyl group from methylated DNA, allowing genes to become transcribed and expressed.
Explain histone modification.
Adding an acetyl or methyl group to a histone changes the arrangement of a nucleosome (histones grouped together) making it more/less DNA accessible to RNA polymerase.
Histone acetylation - addition of acetyl group to a LYSINE which opens up the histone structure and activates chromatin, allowing transcription.
Histone methylation - addition of methyl group to a lysine in the histone structure which tightens it. Depending on its position, methylation can inactivate or activate gene expression.
Explain non coding RNA.
Its non coding RNA that is transribed from DNA but not translated into proteins. It can inactivate genes/chromosomes preventing gene expression.
