Overview
This lecture explains gene expression and gene regulation in both prokaryotic and eukaryotic cells, covering mechanisms at different cellular stages and their significance for cell function and disease.
Gene Expression Basics
- Gene expression is when a gene is used to make a functional product, often a protein.
- The process often involves transcription (DNA to mRNA) and translation (mRNA to protein).
- Not every gene is expressed all the time; expression is selective and regulated.
Gene Regulation
- Gene regulation controls whether and how much a gene is expressed.
- In prokaryotic cells, gene regulation mostly impacts transcription.
- Eukaryotic cells regulate genes at multiple stages: transcription, post-transcription, translation, and post-translation.
Prokaryotic Gene Regulation
- Prokaryotes lack a nucleus, so transcription and translation occur together in the cytoplasm.
- Operons are common in prokaryotes; an operon contains grouped genes with a shared promoter and operator.
- The Lac Operon is regulated by a repressor that blocks transcription unless lactose is present, which removes the repressor and allows gene expression.
Eukaryotic Gene Regulation
- Eukaryotes use transcription factors (regulatory proteins) that bind DNA to promote or repress transcription.
- Enhancer sequences can increase transcription even from a distance.
- DNA can be tightly packed by histones with methyl groups (epigenetic marks), which can inhibit transcription.
- mRNA processing (removing introns, keeping exons) regulates what portion of RNA gets expressed.
- eIF-2 protein can be phosphorylated to block translation initiation.
- After translation, chemical modifications or tagging with ubiquitin can alter protein function or signal degradation.
Environmental Influences
- Environmental factors like nutrient availability or UV exposure can impact gene expression through effects on transcription factors or protein modifications.
Importance of Gene Regulation
- Proper gene regulation is critical for cell function and health.
- Misregulation can lead to diseases like cancer, where genes driving cell division are abnormally activated.
Key Terms & Definitions
- Gene Expression — process of using a gene’s information to make a functional product (often a protein)
- Transcription — copying a gene’s DNA into mRNA
- Translation — converting mRNA into a protein
- Transcription Factor — protein that increases or decreases transcription of a gene
- Operon — cluster of genes regulated together in prokaryotes
- Repressor — protein that blocks transcription by binding to DNA
- Enhancer — DNA sequence far from the gene that increases transcription
- Introns — non-coding RNA segments removed before translation
- Exons — coding RNA segments that remain and are translated
- eIF-2 — eukaryotic initiation factor for translation
- Epigenetics — heritable changes to DNA or histones that affect gene expression without altering DNA sequence
- Ubiquitin — protein tag that signals degradation
Action Items / Next Steps
- Review examples of operons, especially the Lac Operon.
- Read about transcription factors and their roles in gene regulation.
- Study the differences in gene regulation between prokaryotes and eukaryotes.