7.2 Factors affecting gene expression Flashcards
What are transcription factors?
Proteins that bind to DNA
Where do TFs bind?
Specific base sequences
- Promoter - Enable binding of RNA polymerase and therefore promote transcription
- Enhancer - Make the gene more/less open to RNA polymerase by changing chromatin structure. Either stimulate or prevent transcription
What is RNA splicing?
Post-transcriptional modification of mRNA
How does RNA splicing result in different products from a single gene?
Eukaryotes produce more proteins than they have genes
RNA splicing results in different products from a single gene by:
1. pre-mRNA is produced from transcription
2. Introns are removed from mRNA before translation, leaving the exons
3. Spliceosomes can produce mature mRNA using different exons from a gene or organising them differently
4. Results in different polypeptides from the same gene to produce several different versions of mature functional RNA
What is pre-mRNA
A transcript of the whole gene
What is a spliceosome?
Enzyme complexes that act on pre-mRNA, joining exons together
Define epigenetics
The ways in which the expression of genes can be controlled and modified in order to produce the range of cell types and functions found in organisms
What are 3 methods of epigenetic control?
- DNA methylation
- Histone modification
- non coding RNA
How does DNA methylation control gene expression?
Addition of a methyl group to a cytosine in the DNA prevents transcription. Affects histone structure to make more/less DNA accessible to RNA polymerase
What are histones?
Proteins that act as a support for DNA molecules in chromatin. They are grouped into nucleosomes.
How does histone modification control gene expression?
- Acetylation - addition of an acetyl group to one of the lysines in the histone structure. Opens up to structure and activates the chromatin, allowing genes in that area to be transcribed
- Methylation - addition of a methyl group. Can cause activation/inactivation depending on the position of the lysine
What is ncRNA
The large proportion of RNA produced by transcription that is never translated
How does ncRNA control gene expression?
Inactivates genes and chromosomes and preventing gene expression as a cell becomes specialised
What is cell differentiation?
Unspecialised cells switching different genes on and off as needed to become specialised cells
How are epigenetic modifications important in cell differentiation?
Epigenetic controls cause a cell to produce only its own specific proteins
