Overview
This lecture explains gene expression and gene regulation, focusing on how cells control when and how genes are used to make proteins, with examples from both prokaryotic and eukaryotic cells.
Gene Expression Basics
- Gene expression is when a gene is used to make a functional product, often a protein.
- The process involves transcription (DNA to mRNA) and translation (mRNA to protein).
- Not all genes are expressed in every cell; cells regulate which genes are turned on or off.
Gene Regulation and its Importance
- Gene regulation controls whether a gene is expressed, allowing cells to use only necessary genes.
- Regulation is important to avoid waste and ensure proper cellular function.
- Abnormal gene expression is linked to diseases such as cancer.
Prokaryotic Gene Regulation
- Prokaryotes have DNA in the cytoplasm, so transcription and translation happen together.
- Most gene regulation occurs at the transcription level.
- The Lac Operon is an example: a repressor blocks transcription when lactose is absent, but lactose disables the repressor when present.
Eukaryotic Gene Regulation
- Eukaryotes have multiple points for gene regulation: during transcription, post-transcription, translation, and post-translation.
- Transcription factors are proteins that increase or decrease transcription by binding to DNA regions like promoters and enhancers.
- Environmental factors can affect gene expression by influencing transcription factors.
Regulation Examples in Eukaryotes
- Post-transcription: Introns (non-coding regions) are removed from mRNA, leaving exons to be translated.
- Translation: eIF-2, a protein needed to start translation, can be inactivated by phosphorylation, blocking protein production.
- Post-translation: Chemical modification or attachment of ubiquitin to proteins can alter their function or signal degradation.
Epigenetic Regulation
- Chemical marks (like methyl groups) on DNA or histones affect how tightly DNA is packed, controlling transcription accessibility.
- Tightly packed DNA with methylation can block transcription; removing methyl groups can enable gene expression.
Key Terms & Definitions
- Gene expression — Use of a gene to make a functional product, typically a protein.
- Gene regulation — Control over when and how genes are expressed.
- Transcription — Copying DNA into mRNA.
- Translation — Using mRNA to build a protein.
- Transcription factor — Protein that regulates transcription by binding to DNA.
- Operon — Cluster of prokaryotic genes regulated together.
- Lac Operon — An operon in bacteria that controls genes needed to break down lactose.
- Introns — mRNA sections removed during processing.
- Exons — mRNA sections that code for proteins.
- Epigenetics — Heritable changes in gene expression not caused by DNA sequence changes.
- Ubiquitin — Protein that tags other proteins for degradation.
Action Items / Next Steps
- Review examples of gene regulation (Lac Operon, eIF-2).
- Watch related videos or read about gene regulation mechanisms in prokaryotes and eukaryotes.
- Prepare for questions about differences in gene regulation between cell types.