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In this article, we will explain transcription factors are proteins that bind to DNA and play their role in the control of gene expression in eukaryotes by decreasing or increasing the rate of transcription. Moreover, we will also discuss how gibberellin activates genes by causing the breakdown of DELLA protein repressors, which normally inhibit factors that encourage transcription.
We all have transcription factors inside our bodies that keep our cells running. Transcription factors refer to the proteins that control (regulate) the transcription of genes. The human body has several transcription factors. Not only the human body, but birds, trees, and even fungi have transcription factors. Transcription factors are critical for an organism because they ensure that the right genes are expressed in the right cells of the body at the right time.
Transcription: The Main Control Point
The process of transcription copies (transcribes) a DNA sequence into an RNA molecule. Transcription is a critical step in utilizing information from a gene to create a protein.
In the next section of the article, we will discuss what is gene expression.
What is Gene Expression?
Gene expression is when DNA is employed to create the protein it specifies. For several genes, transcription is the main on/off control point.
- In case a gene is not transcribed in a cell, then it cannot be employed to create a protein in that cell
- If a gene gets transcribed (copied), then there is a probability that it is going to be expressed which means that it is going to be used to create a protein. Generally, the more the gene undergoes transcription, the more protein it will make
- How many genes will be transcribed in controlled by different factors? For example, how tightly a gene’s DNA is wound around its supporting proteins to create chromatin can potentially affect whether a gene is available for transcription or not.
- Proteins known as transcription factors play a crucial role in controlling (regulating) the transcription. These vital proteins help in determining which genes are active in each cell of the human body.
In the next section of the article, we will explain transcription factors are proteins that bind to DNA and play their role in the control of gene expression in eukaryotes by decreasing or increasing the rate of transcription.
Gene Control: Transcription Factors
Prokaryotes employ operons to regulate (control) the expression of genes within cells. On the other hand, eukaryotes also employ transcription factors in controlling the expression of the gene. We have already discussed above that a transcription factor refers to a protein that controls the transcription of genes by binding to a particular region of DNA. They do so to ensure that the genes are expressed in the right cells, at the right time, and at the right level.
According to an estimate, approximately 10% of human genes code for transcription factors. There are many types of transcription factors that have different effects on gene expression. This is relatively still a fresh idea of research and scientists are still struggling to comprehend the functioning of different transcription factors. Transcription factors enable organisms to respond to their environment. Some hormones become effective through transcription factors.
In the next section of the article, we will discuss how transcription factors work.
Working of Transcription Factors
Some transcription factors bind to the promoter region of the gene which either enables or stops the transcription of the gene from occurring. It implies that the presence of transcription factor can have one of the following two effects:
- The rate of transcription of the gene is enhanced
- The rate of transcription of the gene is declined
For instance, PIF is a transcription factor present in the plant that stimulates (triggers) the transcription of the amylase gene.
In the next section of the article, we will discuss how gibberellin activates genes by causing the breakdown of DELLA protein repressors, which normally inhibit factors that encourage transcription.
Gene Control: Gibberellin
Plant cells employ transcription factors in the same way as animal cells. Gibberellin refers to a hormone that is present in plant cells like barley and wheat. This hormone controls the germination of seeds by stimulating the synthesis of the amylase enzyme. It achieves this by affecting the transcription of the amylase gene. The amount of mRNA present for amylase increases when gibberellin is applied to a germinating seed.
Mechanism
The breakdown of DELLA protein by gibberellin is critical for the synthesis of the enzyme amylase. The following components play their role to achieve this:
- Repressor protein DELLA
- Transcription factor PIF
- Gibberellin
- Gibberellin receptor and enzyme
- The promoter of the amylase gene
- Amylase gene
The process takes place like this:
- The binding of DELLA protein to PIF prevents it from binding to the promoter of the amylase gene so no transcription can take place
- The binding of gibberellin to a gibberellin receptor and enzyme begins the breakdown of the DELLA
- PIF is not bound to DELLA protein any longer, hence it binds to the promoter of the gene amylase
- Transcription of the gene amylase starts and amylase is produced
Gene Control: Oestrogen
In mammals, the hormone oestrogen plays its role in controlling the oestrus cycle and the production of sperm. Oestrogen refers to a lipid-soluble molecule and hence it can diffuse through the plasma membrane of the cells. After that, it moves to the nucleus and binds to an oestrogen receptor. Actually, these receptors are transcription factors that start transcription for several different genes by binding to their promoter regions.
Once they are bound, oestrogen causes the receptor to alter its shape. Consequently, the receptor goes away from the protein complex it is usually attached to and binds to the promoter region of one of its target genes. This enables the RNA polymerase to bind and start transcribing that gene.
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