Gene Expression Regulation in Eukaryotes

Regulation of Gene Expression in Eukaryotes

• All cells in an organism contain the entire DNA, but only specific genes are turned on in each cell type.
• Genes expressed determine a cell's function, like liver enzymes produced by liver cells, unlike those in stomach cells.
• A typical human cell expresses approximately 20% of its protein-coding genes at any given time.
• Specialized cells, such as muscle and nerve cells, express even fewer genes.
• However, every cell contains a complete genome, differing only in which genes are expressed.
• Cell type differences arise due to differential gene expression, the expression of different genes by cells with the same genome.
• Gene expression can lead to diseases such as cancer due to abnormalities.
• Gene expression is regulated at multiple stages.

How Cells "Decide" Which Genes to Turn On

• Cell types and their specific environment/internal states influence gene expression patterns.
• Gene expression is influenced by information from both inside and outside the cell.
• Intracellular information includes proteins inherited from parent cells, DNA damage status, and available ATP.
• Extracellular information consists of cell signaling, mechanical signals from the extracellular matrix, and nutrient availability.

Chromatin Structure Regulation

• Chromosomes are tightly compacted DNA around proteins during cell division.
• Chromatin is less tightly packed DNA around proteins.
• Histones are proteins around which DNA wraps.
• Nucleosomes are grouped histones together.
• Heterochromatin is tightly packed chromatin, reducing transcription.
• Euchromatin is loosely packed chromatin, allowing transcription.

Regulation of Transcription Initiation

• Transcription involves RNA polymerase II and transcription factors.
• RNA polymerase II attaches to the promoter (TATA box) to start transcription.
• Control elements are non-coding DNA sequences where transcription factors bind.
• Enhancers are control elements far from a gene that can turn transcription on or off.
• Activators bind to enhancers to activate a gene's transcription
• Repressors hinder gene expression by blocking activators from binding to enhancers.

Post-Transcriptional Regulation

• Gene expression isn't solely determined by transcription, but also by mRNA processing, degradation, translation initiation, and protein processing/degradation.

• RNA processing involves the addition of a cap, a poly-A tail, and the removal of introns. Alternative RNA splicing can result.

• mRNA Degradation affects the duration it's available for translation, and is influenced by its poly-A tail length. In prokaryotes, mRNA has a short life, while in eukaryotes it has a longer life span.

• Initiation of Translation is regulated by proteins binding to mRNA, affecting ribosome attachment.

• Protein Processing and Degradation involve modifications and breakdown of proteins to create functional molecules.

• Proteasomes are giant protein complexes that degrade proteins.

Noncoding RNAs and Gene Expression Regulation

• Non-protein-coding DNA in cells plays a role in gene expression.
• microRNAs (miRNAs) can degrade mRNA or block its translation.
• RNA interference (RNAi) and small interfering RNAs (siRNAs) function similarly to miRNAs, associating with proteins to block gene expression.