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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

 

A human cell, a eukaryotic cell, contains some 21,000 genes. Some of these are expressed in all cells all the time. These so-called They are responsible for the routine metabolic functions (e.g. respiration) which are common to all cells. Some are expressed as a cell enters a particular pathway of differentiation. Some are expressed all the time in only those cells that have differentiated in a particular way.  For example, a plasma cell expresses continuously the genes for the antibody it synthesizes. Some are expressed only as conditions around and in the cell change. For example, the arrival of a hormone may turn on (or off) certain genes in that cell.
 Cellular functions  are determined by the thousands of genes that are expressed in that cell. By altering the quantity and kind of proteins produced, the cell can self-regulate its operations by regulating informational flow  from DNA to RNA to protein.
Gene regulation is the process of controlling which genes in a cell’s DNA are expressed i.e., Which gene is used to make a functional product such as a protein. Different cells in a multicellular organism may express different sets of genes in spite of containing the same DNA. The set of genes expressed in a cell determines the set of proteins and functional RNAs it contains and this determines its unique properties.

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.

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Chapter-3 Why Gene expression should be regulated? by Dr.V.Malathi is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License, except where otherwise noted.

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