Main Body
Chapter-3 Why Gene expression should be regulated?
Why Gene expression should be regulated?
Dr.V.Malathi
Learning Objectives
By the end of this section, readers will be able to:
- Discuss why every cell does not express all of its genes.
- Describe the importance of gene expression regulation
- Explain the stages at which gene expression can be regulated
GENE REGULATION
In eukaryotes like humans, gene expression involves many steps. Gene regulation can occur at any of these steps. However basically many genes are regulated at the level of transcription.The concentration of a protein in a cell is determined by the the equilibrium between its metabolic pathways for synthesis and degradation.
Protein formation begins with transcription and continues with translation . The types and concentrations of mRNA molecules present in a cell determine the cell’s function. Every cell creates thousands of transcripts per second. The gene expression is mainly regulated during the transcriptional initiation. One mRNA molecule can produce several proteins, making RNA transcription an effective control point.
Eukaryotes have an additional degree of regulation provided by post transcriptional processing in the nucleus before being exported to the cytoplasm for translation. While in prokaryotes due to the close proximity of the ribosomes to the nascent mRNA molecules, translation starts even before the transcription is completed .
The gene expression regulation may occur even after transcription . For instance, following fertilization during embryonic developmental stages gene expression is regulated at the level of translation. Hence, many maternally derived mRNA transcripts are present in eggs as a ready supply for translation following fertilization.
In eukaryotic cells the level of protein degradation is connected to cellular activities. This can be well illustrated by the role of cyclins. are regulatory proteins that regulate the various phases of cell cycle. Each phase produce a characteristic type of cyclins and a cell must breakdown the cyclin that is specific to that phase of the cell cycle before it can move on to the following phase. A cyclin’s inability to be degraded prevents the cycle from continuing the cell cycle. This example thus helps us to understand how appropriate gene expression and protein levels determine the functions of a cell.
These are genes expressed in all cells at all time
Regulatory proteins that regulate various phases of cell cycle.