Prokaryotic organisms are known as the single-celled organisms that lack a cell nucleus, and their DNA floats freely in the cell cytoplasm. For a protein to be synthesized, both processes of transcription and translation almost occur simultaneously. When the resulting protein is no longer needed, the transcription process stops. As a result, the primary method to control what type of protein and how much of each protein is expressed in a prokaryotic cell is by the regulation of the DNA transcription process. All of the subsequent steps occur automatically. When more protein is required, more transcription occurs. Therefore, in prokaryotic cells, the control of gene expression is mostly at the transcriptional level.
Eukaryotic organisms are known as multi-celled organisms and in contrast, they have intracellular organelles that add to their level of complexity. In the eukaryotic cells, the DNA is contained inside the cell’s nucleus and there it is transcribed into RNA. The newly synthesized RNA is then transported out of the nucleus and into the cytoplasm, and in the cytoplasm, ribosomes translate the RNA into protein. Both processes of transcription and translation are physically separated by the nuclear membrane of the cell’s nucleus, transcription occurs only within the nucleus, as mentioned before translation occurs only outside the nucleus and in the cytoplasm. Also, the regulation of gene expression can occur at all the stages of the process. Regulation may occur when DNA is uncoiled and loosened from nucleosomes to bind transcription factors (known as epigenetic level), or when the RNA is transcribed (known as transcriptional level), or when RNA is processed and exported to the cytoplasm after it is transcribed in the nucleus (known as post-transcriptional level), or when RNA is translated into protein (known as translational level), or after the protein has been made (known as post-translational level).
Genome editing/CRISPR
The CRISPR technology can make precise changes in the human DNA by slicing out the incorrect portion of the gene and replacing it by a correct portion. It is a complicated process, but you can simply put, “guide” RNA and a bacterial enzyme, called Cas-9, and bind to a cut DNA. A repair template with the desired change is inserted where the DNA has been cut. Also, multiple DNA edits can be made simultaneously. Editing DNA with CRISPR has many advantages. For example, genome editing can potentially prevent or treat genetic diseases such as cystic fibrosis, hemophilia and sickle cell anemia. Researches are also being done on DNA editing in the treatment of more complex diseases, like cancer. Although CRISPR technology is precise, it is not very perfect. Sometimes it cuts DNA that is similar to the guide RNA, but not the exact. CRISPR has been one of the biggest scientific achievements of the century.
Now to move on to another technique called Gene Therapy. Gene therapy involves altering the genes inside your body's cells in the effort to treat disease. Gene therapy replaces or adds a new gene to cure diseases and to improve the body's ability to fight disease. Gene therapy holds promise for treating a wide range of lethal diseases, such as cancer, cystic fibrosis, heart disease, diabetes, hemophilia and also AIDS.
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Researchers are considering several ways to do this, such as:
- Replacing mutated genes. Some cells become diseased because certain genes work incorrectly or even no longer work at all. Replacing these defective genes may help treat certain diseases. For example, a gene called p53 prevents tumor growth. Several types of cancer are related to problems with the p53 gene. If the defective p53 gene could be replaced, it might trigger the cancer cells to die.
- Fixing mutated genes. Mutated genes that could cause diseases can be turned off so that they no longer promote disease, or healthy genes that can help prevent disease could be turned on so they could inhibit the disease.
- Making diseased cells more evident to the immune system. In some diseases, your immune system doesn't attack diseased cells because it doesn't recognize them. Gene therapy could be used to train your immune system to recognize cells that can be a threat.
Gene therapy technique has some potential risks. A gene can't be inserted directly into your cells easily. It usually has to be delivered using a carrier (a vector). The most common gene therapy vectors are usually Viruses. Researchers remove the disease-causing genes from the viruses, replacing them with genes needed to stop the disease. The specific procedure you receive will depend on the disease you have also, the type of gene therapy being used. In one type of gene therapy:
First you may have blood drawn or get bone marrow removed from your hipbone with a large needle. Then, the cells from the blood or the bone marrow are exposed to the virus or other type of vector that contains desired genetic material. After that and once the vector has entered the cells, those cells are injected back into your body through a vein or into a tissue. Viruses aren't the only vectors that can be used to carry altered genes into your body's cells. Other vectors being studied include:
- Stem cells. These are the cells from which all the other cells in your body are created.
- Liposomes. These fatty particles have the ability to carry the altered genes to the target cells and pass the genes into your cell's DNA.
The choosing of the vector should be justified with regards to the tropism of the wild type virus/bacterium. The indication and the therapeutic concept along with the target cells will impact choosing of the vector. The target population might be vulnerable for example pregnant women, children, elderly and immunosuppressed. The clinical development will take into account the epidemiology of the disease and specificities of the populations in the indication. In case a Gene Therapy Medicinal Product (GTMP) is specifically indicated for use in pregnant women for example applied during pregnancy, careful ante-natal monitoring of mother and fetus should be done. Also, post-partum long term follow-up of the mother and the child should be performed. For children long-term effects of the GTMP should be considered and monitored. In case of a predicted risk including events with a late arrival (e.g. tumorigenicity), measures to detect the signal and to lessen this risk should be applied. Clinical trials of gene therapy in people have shown some success in treating certain diseases, for example: 1st Severe combined immune deficiency, 2nd Hemophilia, 3rd Blindness caused by retinitis pigmentosa and 4th Leukemia.
In conclusion gene expression is 2 stages Transcription which consists of 4 steps (Initiation, Elongation, Termination and Processing) and Translation that consists of (initiation, Elongation, Termination and Post-Translation), we mentioned the Gene Control Regions which consist of (Start, Promoter, Enhancers and Silencers), and we discussed the Gene Regulation as it is a label for the cellular processes, it is how a cell controls which genes out of the all the genes in its genome are “turned on” and which are “turned off”, and we mentioned the differences and properties of this process in Prokaryotic and Eukaryotic organisms and we said that prokaryotic organisms both processes of transcription and translation almost occur simultaneously and that the control of gene expression is mostly at the transcriptional level, but in eukaryotic organisms both processes of transcription and translation are separated by the nuclear membrane, transcription occurs only within the nucleus, and translation occurs only within the cytoplasm and the regulation of gene expression can occur at all the steps of the process. Then we mentioned the Gene Editing as it can make changes in the human DNA by slicing out the incorrect portion of the gene then replacing it by a new correct portion, this technique can be done by adding a guide RNA and a bacterial enzyme called Cas-9 and bind to a cut DNA. A repair template is inserted where the DNA has been cut. We moved on to a similar technique called the Gene Therapy in which we replace or add a new gene to cure diseases and improve your body's ability to fight diseases, we said there are several ways to do this, for instance: Replacing mutated genes, Fixing mutated genes, Making diseased cells more evident to the immune system, we also mentioned that a gene can't be inserted directly into your cells, it has to be delivered using a vector usually a virus. And finally, I just want to say Gene expression and regulation and their studies are very important, because we can invest in them to cure and improve millions of lives.
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