Your cart is currently empty!
M03.03.05 Production of Prokaryotic Messenger RNA (mRNA)
Understanding the structure and expression of prokaryotic messenger RNA (mRNA) is fundamental to molecular biology. This document outlines the key processes involved in the transcription of prokaryotic genes.
Structure of Prokaryotic Genes
Figure I-3-4 illustrates the typical structure of a prokaryotic gene coding for a protein, highlighting crucial elements such as the promoter, coding regions, and untranslated regions (UTRs).
Key Features of Prokaryotic Genes
- Promoter Region: Contains consensus sequences (Pribnow box and –35 sequence) that direct RNA polymerase binding.
- Transcription Start Site: The site where transcription initiates, indicated as +1.
- Untranslated Regions: Regions flanking the coding sequence that play roles in regulation and translation initiation.
Events in the Expression of Prokaryotic Genes
The following steps outline the process of transcription in prokaryotes:
| Step | Description |
|---|---|
| 1. Promoter Recognition | RNA polymerase, aided by sigma factor, binds to the promoter, unwinding the DNA strands. |
| 2. Initiation of Transcription | Transcription begins at the +1 base pair, and the sigma factor is released. |
| 3. Elongation | Core RNA polymerase synthesizes mRNA in the 5′ to 3′ direction while moving along the template strand (3′ to 5′). |
| 4. Termination | Transcription halts at termination signals: – Rho-Independent Termination: RNA forms a hairpin loop, promoting dissociation from the DNA template. – Rho-Dependent Termination: Rho factor displaces RNA polymerase from the RNA. |
| 5. Simultaneous Transcription and Translation | In bacteria, translation can start before transcription ends, facilitated by ribosome binding to the Shine-Dalgarno sequence. |
| 6. Protein Synthesis | The ribosome translates mRNA in the 5′ to 3′ direction, synthesizing a protein from the amino terminus to the carboxyl terminus. |
Types of mRNA in Prokaryotes
- Monocistronic mRNA: Encodes a single protein; transcribed from a single gene.
- Polycistronic mRNA: Encodes multiple proteins; transcribed from an operon containing related genes (e.g., lactose operon).
Points to Remember
- Prokaryotic mRNA lacks introns, allowing simultaneous transcription and translation.
- The Shine-Dalgarno sequence is critical for ribosome recognition and initiation of translation.
- Transcription terminates through either rho-independent or rho-dependent mechanisms.
Bibliography
- Lodish, H., Berk, A., Kaiser, C. A., Krieger, M., Scott, M. P., & Bretscher, A. (2016). Molecular Cell Biology (8th ed.). W.H. Freeman.
- Alberts, B., Johnson, A., Lewis, J., Raff, M., Roberts, K., & Walter, P. (2014). Molecular Biology of the Cell (6th ed.). Garland Science.
- Becker, W. M., Kleinsmith, L. J., & Hardin, J. (2013). The World of the Cell (7th ed.). Pearson.