7- factors affecting gene expression Flashcards
transcription factors
Specialised proteins that regulate gene expression by binding to specific DNA sequences and controlling the transcription of mRNA from DNA.
how transcription factors work
• DNA binding: Transcription factors identify and bind to specific DNA sequences, often located in the promoter and enhancer regions of a gene.
• Activation or repression:
Transcription factors can either activate or suppress the
transcription process. Activation accelerates transcription, while repression slows it down.
necessity of transcription factors in activation
• For a gene to be transcribed, RNA polymerase must attach to DNA at the promoter.
• In bacteria, RNA polymerase attaches to DNA at the promoter directly.
• In humans and other eukaryotes,
RNA polymerase can only attach with the help of transcription factors.
activation
• This is done by recruiting RNA polymerase to the transcription start site.
• Transcription factor binding:
Transcription factors bind to the promoter region.
• Activator proteins: Activator proteins bind to the enhancer sequence further upstream.
• Formation of transcription complex: Various regulatory proteins converge as the DNA molecule bends and loops, forming a combined transcription complex.
• Activation of RNA Polymerase:
This transcription complex activates RNA polymerase, which traverses the DNA molecule, transcribing it into mRNA.
combinatorial control
Multiple transcription factors often collaborate to regulate gene expression, providing a high degree of control and specificity.
importance of transcription factors
• Regulation of gene expression:
Transcription factors are integral to controlling gene expression, influencing the function and behaviour of cells.
• Cellular differentiation and
development: They are essential for cell differentiation and development, affecting the specific gene expression patterns that lead to the formation of diverse cell types in an organism.
• Response to environmental changes:
Transcription factors can react to internal and external cellular signals, enabling cells to adapt to varying conditions.
• Implications in disease: Changes in transcription factor function can lead to diseases like cancer through abnormal gene expression.
post transcriptional modification
Processes that modify mRNA molecules after they are transcribed from DNA in eukaryotic cells.
RNA splicing
A post-transcriptional modification event where introns (non-coding sequences) are removed from the pre-mRNA and exons (coding sequences) are joined together.
need for RNA splicing
• Transcribed mRNA is known as pre mRNA as it contains non-coding regions called introns.
• Before the pre mRNA can leave the nucleus, it has to be modified, and the non-coding regions have to be excised, leaving only the coding regions called exons.
role of RNA splicing in protein diversity
• Alternative splicing: This process allows a single gene to produce multiple different mRNA molecules. Different combinations of exons are included or excluded from the final mRNA, leading to mRNAs that code for different proteins.
• Protein diversity: Each of the different mRNA molecules produced through alternative splicing can be translated into a different protein. This leads to a wide variety of proteins with potentially different functions, properties, or localisation within the cell.
importance of RNA splicing
• Enhancing biological complexity:
Despite a limited number of genes, alternative splicing allows organisms to generate a much larger number of distinct proteins, enhancing their biological complexity.
• Regulation of gene expression:
Alternative splicing can also be a way to regulate gene expression, with different mRNA variants being produced in different tissues, at different
developmental stages, or in response to different signals.
misregulation and diseases
Errors in RNA splicing can lead to the production of incorrect or harmful proteins that can contribute to diseases, including many types of cancer, neurodegenerative diseases, and spinal muscular atrophy.
epigenetic modification
• Heritable alterations in structures other than the DNA sequence.
• These regulations refer to control at the chromosomal level (e.g. DNA accessibility and chromatin structure).
non-coding RNA
These are RNA molecules that do not code for a protein but can influence gene expression.
RNA interference (RNAi)
A biological process where non-coding RNAs inhibit gene expression or translation, by neutralising targeted mRNA molecules.
long non-coding RNAs (IncRNAs)
They regulate gene expression at various levels, including chromatin modification, transcription, and post-transcriptional processing.
histone modification
• Histones are proteins that DNA wraps around.
• Their modification can lead to changes in gene expression.
acetylation
Addition of an acetyl group to a histone protein.
Acetylation results in loose packing of nucleosomes. Transcription factors can bind the DNA, and genes are expressed.
methylation
Addition of a methyl group to a histone protein.
Methylation causes nucleosomes to pack tightly together.
Transcription factors cannot bind the DNA, and genes are not expressed.
DNA methylation
A process by which methyl groups are added to the DNA molecule.
DNA methylation in CpG sites
Highly methylated DNA is coiled up and restricts transcription. This often leads to gene silencing.
DNA demethylation
The removal of methyl group can activate the gene expression. This process is crucial during development and cellular differentiation.
ensuring cell differentiation through epigenetic modification
Through mechanisms such as DNA methylation and histone modifications, certain genes can be activated or silenced. This determines the specific set of genes that are expressed in a particular cell type, thus guiding the cell towards a specific developmental pathway.
importance of epigenetic modification in cell differentiation
• Development and diversity
→ Epigenetic modifications allow for the differentiation of various cell types from the same genomic DNA, leading to the development of diverse tissues and organs in an organism.
• Maintenance of cell identity
→ Once a cell has differentiated into a specific type, epigenetic marks help to maintain this identity across cell divisions, ensuring stability and proper function of tissues and organs.
• Disease prevention → Proper control of cell differentiation through epigenetic modifications is essential for preventing diseases like cancer, where a loss of differentiation features is a common characteristic.
