Gene expression: what it is and why it is important
Gene expression is the set of processes that lead the information contained in a gene to be converted into a functional molecule. All events of gene expression allow the transcription of DNA into messenger RNA (mRNA) and from the latter, through translation, to the formation of a protein. Typically, the expression contained in a gene is made up of DNA or double-stranded nucleic acid made up of nitrogen bases, deoxyribose (a sugar), and phosphate groups.
The control of gene expression
Gene expression control is the process by which genetic information passes from genes to proteins, that is, from genotype to phenotype. Furthermore, the control of gene expression allows cells to produce only the proteins necessary for their formation and in response to changes in the environment. In prokaryotes, the genes that encode enzymes are often in series and controlled by a promoter sequence and an operator sequence by binding with regulatory proteins; these functional units form operons. The link between regulatory proteins and the operator activates or deactivates transcription and, therefore, the production of enzymes in response to changes in the environment. Gene expression is more complex in multicellular eukaryotes than in prokaryotes. Here, the cells differentiate during embryonic development.
Each one has different genes that code for certain proteins while retaining the entire genetic heritage. The way DNA folds back into the eukaryotic chromosome helps regulate gene expression. In fact, the spiraling of DNA prevents the expression of genes as it does not allow the enzyme RNA polymerase to make contact with DNA. In order for a gene to be transcribed, histones must detach themselves from DNA. The most important stage of gene regulation is the regulation of transcription in both prokaryotes and eukaryotes. Regulation in eukaryotes appears as a network of proteins that interact with each other and with DNA to activate or deactivate genes. In addition to RNA polymerase, activation of a eukaryotic gene also involves transcription factors, including inductors and repressors, which respectively accelerate or slow down transcription.
What is gene expression for?
These processes are fundamental for the survival of the cell and for controlling its internal and external functions.
What are the control points, and where are they located?
Gene expression occurs mainly in the nucleus and cytosol of the cell. There are several important and indispensable control points for the long series of processes to follow a correct course.
In the core, there are two controls:
1. a control in the transition from DNA to RNA, the so-called transcriptional control;
2. A further check to verify the different manipulations and modifications of the RNA to make it an mRNA.
1. a control in the transport of RNA;
2. a check in the translation;
3. an event leading to control in mRNA degradation;
4. Finally, a check on the activity of the newly formed protein.
Gene expression: the transcription of information
A fundamental clarification: the DNA duplication process must be clearly distinguished from the transcription process. In the first case, by means of a semi-conservative process, the DNA double helix is replicated, and another double DNA strand will be obtained. In this case, entire regions replicate. The transcription leads from the double helix of DNA to the formation of an RNA strand. In this event, small regions of DNA are copied. RNA polymerase is the enzyme that allows the formation of the RNA strand from DNA. Genes need some enhancers to be transcribed. We have different enhancers for each gene, and this allows combinatorial control.
Their function is to increase the transcription frequency and facilitate this phase of gene expression.
For reasons of simplicity, we will avoid dealing with chromatin condensation and decondensation in this article.
There are two events that take place in the nucleus, therefore in eukaryotes, which are typical of the term of transcription:
1. The capping: addition of a methyl-guanine at the end phosphate 5 'mRNA;
2. The splicing: process in which the introns are removed and exons are joined.
To correctly produce a protein, it is necessary that all the introns are removed, to avoid the presence of amino acids and frameshift mutations.
Gene expression: translation
After the formation of the mRNA has occurred, it must be conveyed and brought to the start of the protein synthesis in the ribosomes.
Another fate is that of mRNA degradation that could occur when it is still attached to ribosomes for protein synthesis.
Some RNA molecules are important for regulating small metabolites and gene expression, i.e., riboswitches.
These regulate translation and are present in bacteria, plants, and fungi. Discovered in 2003, they are important for "turning on" or "turning off" the production of certain proteins. Given their high presence in bacteria, it is useful to mention them because it could open new frontiers for the production of new antibiotics.
What happens once the protein is produced?
When the translation process is completed, we will have the newly formed protein conveyed to the necessary structures through the coatomers and the V-SNARES.
Author: Vicki Lezama