13.1: Introduction
The metabolic potential of cells is flexible, depending on various mechanisms that ultimately determine the levels and activities of proteins that dictate a cell’s metabolic state. We have seen some of these regulatory mechanisms:
- the regulation of transcription by extracellular chemical signals or developmental chemical prompts
- the control of enzyme or other protein activity by allosteric regulation or chemical modification (e.g., phosphorylation or dephosphorylation).
In this chapter, we look at different kinds of post-transcriptional regulation , events somewhere between mRNA transcription and controls on the activity of finished proteins. These control mechanisms are most diverse in eukaryotes.
Like other pathways for regulating gene expression, post-transcriptional regulation begins with extracellular chemical signaling. Responses include changes in the rate of polypeptide translation, and changes in macromolecular turnover rate (e.g., changes in the half-life of specific RNAs and proteins in cells). Regardless of mechanism, each upor down-regulation of gene expression contributes to changes in the steady state of a particular RNA or protein required for proper cell function. In considering posttranscriptional regulation, we will see how cells use specific proteins and different noncoding RNA transcripts to target unwanted proteins or RNAs for degradation.
Learning Objectives
When you have mastered the information in this chapter, you should be able to:
- Explain what it is about C. elegans makes it a model organism for studying development and the regulation of gene expression.
- Compare and contrast the origins and functions of miRNA and siRNA.
- Search for examples of miRNAs, siRNAs, lncRNAs and circRNAs that regulate the expression of specific genes and explain their mechanisms.
- Explain how a riboswitch functions to control bacterial gene expression.
- Explain the origins and roles of bacterial CRISPR-Cas immune system components.
- Explain how eif2 activity is modulated to coordinate red cell heme and globin levels.
- Describe how eukaryotic cells degrade unwanted proteins and speculate on how bacteria might do so
- answer the questions “How did junk DNA arise?” and “Does junk DNA have value?”