Control of Gene Expression: Eukaryotes
This lesson covers:
- What transcription factors are
- Chromatin remodelling
- Epigenetics and histone modification
What are transcription factors?
Transcription factors are proteins that bind to specific DNA sequences to initiate the transcription of genes into mRNA.
mRNA is that is produced during transcription then carries the genetic code from DNA to ribosomes, allowing the production of proteins. Transcription factors therefore have a crucial role in gene expression regulation.
When a gene is 'switched off', transcription factors cannot bind to DNA. This prevents the transcription process and so the synthesis of polypeptides.
Epigenetics and histone modification
Epigenetic regulation involves changes in gene expression without altering the underlying DNA sequence, such as through histone modifications. Histone modifications can influence chromatin structure and gene activity by making DNA more or less accessible for transcription.
Modifications that promote transcription include:
- Acetylation - This process involves adding acetyl groups to histones, decreasing their positive charge and resulting in a looser DNA coil and increased transcription.
- Phosphorylation - Adding phosphate groups to histones also reduces their positive charge, resulting in a looser DNA coil and increased transcription.
A modification that inhibits transcription:
- Methylation - This involves adding methyl groups to histones, increasing hydrophobic interactions and tightening the coiling of DNA, which reduces transcription.
Through these modifications, cells can finely regulate gene expression, adapting to various internal and external stimuli.
Chromatin remodelling
Chromatin structure plays a significant role in gene expression in eukaryotic cells. Negatively charged DNA wraps around positively charged histone proteins to form chromatin.
Chromatin can exist in two forms:
- Heterochromatin - This form of chromatin is densely packed, making it difficult for RNA polymerase to access genes, thus preventing transcription.
- Euchromatin - This is a loosely packed form of chromatin that allows easy access for RNA polymerase, enabling active transcription of genes.
Chromatin remodelling is essential for controlling when and where genes are expressed, ensuring that proteins are produced only when needed. It allows cells to control which genes are active, influence cell function, and respond to environmental signals.