The topics on this page are:
- Gene function summary
There is a lot of information in the chromosomes (chromosomes) inside the cells. It is estimated that the human body has about 30,000 genes. Each gene specifies a genetic code for the RNA molecule. RNA molecules may be directly utilized, may also be used to produce the protein ( Protein synthesis), and insulin (as previously mentioned insulin ). The information within the cell generally flows in a predetermined order, from the form of storage of the information ( DNA ) through the functional form of the information (RNA) to the final product (protein). This pathway is used by all organisms. Below is an illustration of this path:
As can be seen from the above figure, DNA is used to synthesize more DNA templates. This process is called replication ( Replication ), we describe here in detail.
Certain fragments The process of DNA (gene) is referred to for the synthesis of RNA transcription ( Transcription ). We will describe the transcription process in more detail, as changes in certain genes during transcriptional processes play an important role in cancer development.
If these genes are “started” at all times, problems can arise. Changes in our living environment mean that different genes should be “launched” at different times. For example, if we eat a lot of lactose (a sugar in milk), then our body responds by “starting” (transcription) genes that cause the production of enzymes that break down lactose. If it is a different sugar or nutrient, you should “start” the corresponding gene to deal with different substances.
Transcription is to make an RNA copy of a gene . This RNA can direct protein synthesis or be directly utilized within the cell. Containing nucleus ( Nucleus of all cells) are there exactly the same genetic information. As mentioned before, in a certain cell, only a few genes are used for RNA synthesis at any time. In normal cells, the transcription process is strictly regulated as follows:
- Genes must be transcribed at regular times.
- The amount of RNA produced from the gene must be correct.
- Only the genes that are needed can be transcribed.
- “Off” transcription is just as important as “open” transcription.
You can use the above management ratio as a management of a well-designed pipeline, as you can see in the factory. When the production is required, “open” the flow line; when it is not required to be produced, “close” the line.
Human chromosomes (chromosomes) store a lot of information. Each chromosome has a long DNA strand consisting of millions of nucleotides. A gene occupies only a small fragment of a chromosome.
The following animation shows how DNA is organized in a chromosome. The DNA is tightly wound and spiraled to reduce the space occupied, just like winding a wire on a bobbin. The chromosomes shown below have been copied and presented with a signature X shape. The chromosome before cell division is in this state.
In order for transcription to succeed, a method must be used to determine the “start and stop” time of transcription. This “start and stop” time is controlled by certain special proteins. These proteins bind to the starting point of the gene to be transcribed. We refer to these proteins, called transcription factors(transcription factors).
The transcription process is divided into the following steps:
- The transcription factor recognizes the promoter (promoter) of the transcribed gene.
- RNA synthesis enzyme ( Enzyme ) (RNA polymerase) the transcription factor binding site and recognizes the start.
- RNA polymerase makes copies in the direction of the DNA, up to the end of the gene.
- RNA polymerase sheds and RNA is released. This copying process is repeated many times.
- If the replicated RNA contains a protein code, the RNA will leave the nucleus and enter the cytosol.
Note that the gene mentioned above is actually a stretch of nucleotides on a DNA molecule (chromosome).
Functional abnormalities of transcription factors are seen in almost all known cancers. Since transcription factors are so necessary for normal cell activity, their abnormal function can have serious effects on all other parts of the cell. Using the factory’s flow line as a metaphor, the dysfunctional transcription factor will keep the flow line that should have stopped running, producing too many products. And it needs to run, but does not run , resulting in a lack of certain products.
The following example shows transcription factors that are dysfunctional in human cancer:
- P53 (TP53) – A gene that controls the production of p53 transcription factors (proteins) mutates in more than half of cancers. The protein produced by the p53 gene is important because it controls the transcription of genes involved in cell division. More information about the p53 gene is in the chapter on cancer suppressor genes.
- Rb – The protein product of this gene is a transcription factor with interesting functions. In fact, its function is to block other transcription factors. Thus, Rb prevents transcription of the major genes required for cell division. Initially, Rb was described asa genetic variant present in retinoblastoma , and its name was derived from it. Now, we know that Rb proteins play a role in many different cancers. More information about the Rb gene is in the chapter Cancer Inhibition Genes.
- Estrogen Receptor ( ER ) – This protein binds to estrogen that enters the cell. Estrogen is a steroid (ester) hormone secreted by the ovaries. A combination of protein and hormone becomes a transcriptional molecule that cleaves the target cell. This receptor is activated in the female reproductive organs (eg breast, ovary). For this reason, estrogen is considered to be a factor that stimulates the formation of cancer in these areas.
The mechanism of action of estrogen is shown below:
The green ball represents estrogen. Estrogen is a hydrophobic ( Hydrophobic small molecules), which enters the cell by lipid membranes. Once inside the cell, estrogen binds to its receptor ( shown in orange ). The resulting complex binds to DNA within the nucleus, allowing the gene to be transcribed.
Several drugs have been developed to try to block the “starting” effect of estrogen on genes. Tamoxifen, which is commonly used clinically, belongs to such drugs and can partially inhibit estrogenic activity. Tamoxifen is shown in pink in the animation below .
These drugs should slow the growth of tumors that are sensitive to estrogen and its receptors. For more information on estrogen and its receptors, see the chapter “Cancer Treatment”.
The importance of transcription factors for cell division has been repeatedly emphasized. Malignant tumors are caused by uncontrolled cell division. So the next process we want to discuss is cell division. It is important to understand the normal process of cell division, which will help us understand the problems that arise in cell division.
Messenger an RNA ( the mRNA ) after the transcriptional generated by the above-described (Transcription) process, are processed in the nucleus (Nucleus), and then fluid is released into the cell ( the cytosol ) of.
After, the mRNA by ribosomes in the cell sap ( ribosome ) subunit identified by ribosome ‘read’ information to their protein synthesis (protein). Information directing protein synthesis is encoded in the nucleotide sequence that makes up the mRNA. A group of three nucleotides (called codons) is “interpreted” by the ribosome, allowing an amino acid to be inserted into the polypeptide (protein) being synthesized. The animation below shows the process.
After protein synthesis, an active folded structure is obtained to perform its function in the cell. The correct folding, transport, functional play, and ultimate destruction of proteins are strictly controlled and managed.
Genes that control these processes are often damaged in cancer and have dysfunction.
More information about this chapter can be found in the first chapter of The Biology of Cancer by Robert A. Weinberg.
- The DNA in our chromosomes contains genetic information that is transcribed into RNA.
- There are many different kinds of RNA (tRNA, mRNA, rRNA, etc.). They consist of the same ingredients but have different functions, locations, and structures.
- Messenger RNA (mRNA) can be translated into protein. The standard information flow is:
- A series of genes that are always “starting” are very dangerous. Different genes need to be “launched” at different times, depending on the needs and function of the particular cell.
- The purpose of transcription is to form an RNA replica of the gene.
- Transcription factors determine the location of transcription initiation by binding to the starting point of the gene.
- Both p53 , Rb , and estrogen receptors are transcription factors that are dysfunctional in cancer.
- The transcription process can be divided into the following steps:
- The transcription factor recognizes the promoter (promoter) of the transcribed gene.
- An enzyme that synthesizes RNA (RNA polymerase) binds to a transcription factor.
- RNA polymerase makes copies in the direction of the DNA.
- RNA polymerase sheds and RNA is released.
- RNA remains in and out of the cell and enters the cytosol.
- The purpose of translation is to synthesize proteins using the encoded information carried by the mRNA.
- The translation process can be divided into the following steps:
- The mRNA leaves the nucleus and is recognized and bound by ribosomal subunits in the cell lipolysis.
- The ribosome “interprets” three nucleotides (one codon) at a time.
- Ribosomes insert amino acids into a growing protein chain based on codons.
- Protein synthesis stops when the ribosome encounters a stop codon.
- The protein enters a tightly controlled folding process and acquires a fully folded structure.
- Genes that control the correct folding, transport, activity, and eventual destruction of proteins are often compromised or dysfunctional in cancer.