Overview
This lecture explains how gene expression is regulated in prokaryotic and eukaryotic cells, why such regulation is necessary, and at which stages control occurs.
Why Regulate Gene Expression?
- Cells only express necessary genes to conserve energy and resources.
- Gene expression ensures proteins are made at the right time, amount, and location.
- Regulation prevents cells from being overly large due to constant protein production.
- Malfunctions in gene regulation can cause diseases, including cancer.
Mechanisms of Gene Regulation
- Gene expression is the process of turning DNA instructions into RNA and protein.
- Internal chemical mechanisms control when and how much protein is made.
- Regulation includes when to start, how much to make, and when to stop protein synthesis.
Prokaryotic Gene Regulation
- Prokaryotes lack a nucleus; their DNA is in the cytoplasm.
- Transcription and translation in prokaryotes occur almost simultaneously.
- The main control point in prokaryotes is at the transcriptional level.
- When a protein is needed, transcription increases; when not, it stops.
Eukaryotic Gene Regulation
- Eukaryotes have a nucleus where DNA is transcribed to RNA; translation occurs in the cytoplasm.
- Transcription and translation are separated by the nuclear membrane.
- Regulation can occur at multiple levels: epigenetic, transcriptional, post-transcriptional, translational, and post-translational.
- Epigenetic control involves DNA accessibility for transcription factors.
- mRNA processing and export, as well as protein modification and degradation, are additional regulatory steps.
Evolution of Gene Regulation
- Prokaryotes regulate gene expression mainly by controlling transcription levels.
- Eukaryotic regulation became more complex with the evolution of cellular compartmentalization.
- Additional regulatory processes protect cells from infections, e.g., gene silencing against viruses.
Key Terms & Definitions
- Gene Expression — activation of a gene to produce RNA and protein.
- Transcription — synthesis of RNA from a DNA template.
- Translation — synthesis of protein from an RNA template.
- Epigenetics — regulation of gene expression by modifying DNA or chromatin accessibility.
- Post-transcriptional Regulation — control after RNA is made but before it is translated.
- Post-translational Regulation — control after a protein has been made.
Action Items / Next Steps
- Review Table 16.1 for a summary of prokaryotic vs. eukaryotic gene regulation.
- Prepare to study detailed regulatory mechanisms in subsequent sections.