This topic covers the basics of gene expression, including the process by which information from a gene is used to synthesize a functional gene product such as proteins or RNA molecules.
Introduction to Gene Expression
Key concepts, stages, and regulatory mechanisms
| Term | Definition |
|---|---|
| Gene | A DNA segment that contains the instructions for making a functional product (usually a protein or functional RNA). |
| Gene expression | The process by which information encoded in a gene is converted into a functional product. |
| Central Dogma | DNA → RNA → Protein (with some exceptions, e.g., functional RNAs). |
Why it matters: Gene expression determines cell identity, response to stimuli, development, and disease states.
Note: In prokaryotes, transcription and translation can be coupled (occur simultaneously).
| Component | Role |
|---|---|
| RNA polymerase (RNAP) | Catalyzes phosphodiester bond formation; different forms for bacteria (RNAP core) and eukaryotes (RNA Pol I, II, III). |
| Promoter | DNA sequence upstream of the gene where RNAP binds; includes -35 and -10 elements (bacteria) or TATA box (eukaryotes). |
| Enhancers / Silencers | Distant regulatory DNA elements that increase or repress transcription when bound by specific transcription factors. |
| Transcription factors (TFs) | Proteins that recognize DNA motifs, recruit RNAP, and modulate its activity. |
| Termination signals | Sequences that cause RNAP to stop transcription (e.g., rho‑dependent/independent in bacteria; poly‑A signal in eukaryotes). |
Result: A mature mRNA ready for export to the cytoplasm.
| Step | Key Players | Main Events |
|---|---|---|
| Initiation | 40S ribosomal subunit, eIFs, Met‑tRNA, mRNA cap | Assembly of the 80S ribosome at the start codon (AUG). |
| Elongation | 60S subunit, eEFs, aminoacyl‑tRNAs | Peptide bond formation; ribosome moves codon‑by‑codon. |
| Termination | Release factors (eRF1 |