What do transcription factors do? Transcription factors function in the regulation of which genes to be turned on and which genes to be turned off in a cell. By doing so, a cell becomes differentiated and adapted to become a specific type of cell and perform a specific set of functions. For instance, this would tell a muscle cell to turn genes that are pertinent for muscle functions on. Moreover, transcription factors contribute to the following functions:
- Developmental functions: transcription factors respond to different environmental stimuli during the organism's development in order to activate or suppress specific genes.
- Cell signaling: intercellular communication is vital for cell function. Some cells interact with other cells to activate signal transduction, which involves the recruitment of transcription factors.
- Cell cycle regulation: the cell undergoes what is called a cell cycle composed of 4 stages (G1, S, G2, and M). Transcription factors are needed to transition between stages of the cell cycle.
Examples of Transcription Factors
Transcription factor examples vary between organisms and cell types. For instance, transcription factors called the Hox family are vital during development, as they prompt the formation of the body shape. Another example of a transcription factor that is involved in development is the SRY protein. The SRY protein is needed for sex differentiation in human development. The presence of the SRY protein activates genes that are involved in the formation of the male reproductive organ. Another example is the Myc protein, which is involved in regulating cell death (apoptosis) and cell growth.
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Transcription factors control the rate of transcription through binding to the DNA at regions called promoters. Transcription factors can bind alone, or with a multitude of other proteins to form a complex. After that, transcription factors can control transcription by either recruiting RNA polymerase to initiate mRNA synthesis (turning the gene on), or by blocking RNA polymerase function (turning the gene off). There are 3 types of transcription factors: general, specific, and regulatory transcription factors.
General Transcription Factors
General transcription factors, also known as basal transcription factors, bind to the DNA at the promoter region of a gene in order to kickstart transcription. These are the most basic set of transcription factors, and they are necessary for RNA polymerase binding. Common examples of general transcription factors include TFIIA and TFIIB.
Specific Transcription Factors
Specific transcription factors are similar to general transcription factors. Specific transcription factors bind to DNA at regions called enhancers or repressors. They execute their function by altering the orientation of DNA to bring the gene closer to or push the gene farther from the RNA polymerase enzyme, hence activating or repressing the gene. Enhancers and repressors are distal elements of the DNA sequence, meaning that they are at a farther location upstream from the gene, rather than close to it as seen in the case of promoters. Furthermore, specific transcription factors can induce structural changes to the DNA sequence; for instance, specific transcription factors can add methyl groups to the DNA in order to activate or repress the gene.
Regulatory Transcription Factors
Regulatory transcription factors are stimulated by stimuli in the cell such as hormone binding and low levels of certain chemicals such as sterol. An example of regulatory transcription factors is sterol regulatory elements, which are localized in the endoplasmic reticulum and nuclear envelope until activated. Upon activation by cleavage when cellular sterol levels are low, they are translocated to the nucleus where they bind to specific elements of DNA called regulatory elements, thus activating the enzyme necessary for sterol synthesis.
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General transcription factors are protein-based factors that bind to the DNA at regions called promoters; on the other hand, specific transcription factors involve DNA sequences called enhancers or promoters. General transcription factors do not modify the shape or orientation of the DNA sequence, while specific transcription factors bind the DNA in order to bring RNA polymerase closer or further to the gene to be activated or repressed. Regulatory transcription factors function in regulating levels of certain molecules in the cell and are usually activated by cleavage.
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The process of gene expression and protein synthesis is vital for cell structure and function. The cell's genetic material, or DNA, is used as a template to generate mRNA with the help of the enzyme RNA polymerase. This process is known as transcription and is the first step toward synthesizing proteins in a cell. Transcription is regulated by a set of proteins called transcription factors. There are almost 1600 transcription factors in the human genome. Transcription factors play a role in controlling which genes are to be activated and which genes are to be suppressed in cells, which then would provide the cell with a state of differentiation. This is important for development, cell signaling, and cell cycle regulation.
There are three types of transcription factors. The first type is general transcription factors, which bind to regions of DNA called the promoter sequences to either enhance or suppress the gene in proximity to the promoter and initiate the process of transcription. The second type, specific transcription factors, involve enhancer or repressor sequences of DNA that play with the orientation of DNA in order to activate or silence genes. The third type is regulatory transcription factors, which regulate the levels of certain chemicals in the cell.
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Video Transcript
Transcription Factors
Within every cell is a nucleus. Within every nucleus is DNA. And, within that DNA is…you. All of you. Every cell, regardless of what type of cell it is, contains the entire DNA sequence for that individual. So, how do we go from the entire DNA sequence to creating a specific cell? Well, it's…complicated. There's a lot that goes into this, but none of it would be possible without these guys. These are transcription factors, proteins that control the conversion of DNA into RNA. These proteins here are largely responsible for activating the parts of the DNA sequence needed to create a specific cell, so they are pretty important. They can either promote the activation of specific genes or inhibit the activation of others. I guess you could think of them as the lifeguards of the gene pool.
Transcription and Gene Expression
Now, before we get too carried away with our transcription factors here, let's talk briefly about what's going on. As cells replicate, certain genes within the DNA need to be activated in order for that cell to turn into a blood cell or skin cell or whatever it needs to be. For that to happen, the DNA needs to be transcribed, or converted into RNA. The molecule responsible for this transcription is an enzyme called RNA polymerase. So, where do the transcription factors fit into this? Transcription factors are in charge of transcription regulation, which means that they basically tell RNA polymerase where to go. The transcription factors can attract RNA polymerase, promoting the transcription of a gene, or they can block the enzyme, stopping transcription. In short, they control if, when, where, and how efficiently the enzyme RNA polymerase can do its job.
General and Specific Transcription Factors
Now, transcription factors can do all of this by attaching themselves to the enzyme itself, or they can just go straight to the source and attach themselves to the DNA. Where do they do this? It actually depends on what sort of transcription factor we're talking about. Most transcription factors are called general transcription factors. These are the transcription factors that control the beginning of transcription and are sometimes also referred to as basal transcription factors. General transcription factors are very common and are actually required for all RNA transcription. In fact, they are so important to this process that many researchers actually consider them to be a necessary component of life. General transcription factors generally bind to the DNA at promoters, short sections of DNA responsible for initiating the transcription of a particular gene. This is where the entire process kicks off.
From here, transcription can be taken over by another type of transcription factor, called the specific transcription factor, which increase transcription rates and efficiency for a specific gene. While general transcription factors can bind to any site, specific transcription factors can generally only bind to specific genes, but they are often necessary for complete transcription to occur. Rather than attaching to the gene at promoters, specific transcription factors often bind to enhancers, short strands of DNA that can increase the rate of transcription. Specific transcription factors work at enhancers for a more advanced level of regulation over a specific gene.
Say that the transcription factor wants to activate a specific gene, maybe one of the ones responsible for the growth of fingernails. Well, to do that, the general transcription factor needs to bind with the specific promoter associated with that gene. In this case that would be MSX1, not that you needed to know that. So, the transcription factor finds the enhancer associated with the MSX1 gene, binds to it, and the process of transcribing that DNA sequence into RNA can begin. Then, a specific transcription factor can find the enhancer for that gene and speed up the process, and before you know it, you've got nice long fingernails to chew on when you're nervous. And, it's all thanks to your transcription factors.
Lesson Summary
For a specific gene to be expressed, it needs to be transcribed from DNA to RNA. The enzyme responsible for this is called RNA polymerase, but another protein is really the hero here. Transcription factors are proteins that control the conversion of DNA into RNA by attracting or limiting the ability of RNA polymerase to transcribe specific genes. Transcription factors can do this by binding with the enzyme, or by directly binding onto the DNA strand itself. General transcription factors, those that control the beginning of transcription and are required for all RNA transcription, often bind to promoters, short sections of DNA responsible for initiating the transcription of a particular gene. Specific transcription factors, on the other hand, increase transcription rates and efficiency for a specific gene and often bind to enhancers, short strands of DNA that can increase the rate of transcription. Our transcription factors allow complex DNA to become something specific, so these proteins are definitely making a splash.
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