Eleanor Finch
Gene expression is the process by which information from a gene is used to create functional gene products, such as proteins or non-coding RNAs, which ultimately affect an organism's phenotype or observable traits. Gene expression is highly regulated, with control exerted over the timing, location, and amount of a given gene product. This regulation is essential for cellular differentiation, development, and adaptability. Constitutive genes are a type of gene that is transcribed continually, in contrast to facultative genes, which are only transcribed when needed. This distinction between constitutive and responsive gene expression strategies is important when considering growth in changing environments, as the optimal expression level may differ from the average demand for the gene product.
| Characteristics | Values |
|---|---|
| Definition | Constitutive genes are transcribed continually |
| Comparison with other genes | Unlike facultative genes, which are transcribed only when needed, constitutive genes are always transcribed |
| Comparison with housekeeping genes | Housekeeping genes are a type of constitutive gene that is required to maintain basic cellular functions. They are typically expressed in all cell types of an organism. |
| Transcription | Constitutive genes are expressed following interaction between a promoter and RNA polymerase without additional regulation |
| Protein levels | Constitutive transcription does not necessarily mean constant production of protein at an equal rate |
| Expression levels | Constitutive genes are expressed at intermediate levels, providing an immediate benefit when the protein is needed |
| Optimal expression | The optimal constitutive expression level differs from the average demand for the gene product and from the average optimal expression level |
| Responsive vs. constitutive | A responsive expression strategy is favoured by environmental and inter-cellular noise, while the fitness of a constitutive strategy is reduced |
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What You'll Learn
Constitutive genes are continually transcribed
Gene expression is the process by which information from a gene is used to produce functional gene products, such as proteins or non-coding RNAs, ultimately affecting an organism's observable traits or phenotype. Regulation of gene expression is vital as it gives cells the flexibility to adapt to their environment, external signals, and other stimuli. It also gives cells control over their structure and function, forming the basis for cellular differentiation, development, and morphogenesis.
Constitutive genes are a type of gene that is continually transcribed or expressed. They contrast with facultative genes, which are only transcribed when needed. Constitutive genes are expressed following the interaction of a promoter and RNA polymerase without requiring additional regulatory factors or special conditions. While constitutive genes are generally expressed at a constant level, this does not necessarily imply a constant production of proteins. Protein levels are also influenced by the rate of translation and protein/mRNA degradation.
Housekeeping genes, which are required to maintain basic cellular functions, are typically constitutive genes. Examples of housekeeping genes include actin, GAPDH, and ubiquitin. These genes are expressed in all cell types of an organism and are relatively unaffected by experimental conditions. Their expression rates can be used as a reference point in experiments to measure the expression of other genes.
The responsive vs. constitutive expression strategies are important considerations in changing environments. While adjusting protein levels in response to environmental changes can be slow, constitutive expression can provide an immediate benefit when the protein is needed. Studies have shown that constitutive expression can be advantageous even when regulatory machinery is not a factor, and it can increase fitness in certain environments. However, environmental and intracellular noise favour the responsive strategy while reducing the fitness of the constitutive one.
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They are expressed following interaction with RNA polymerase
Gene expression is the process by which information from a gene is used to generate functional gene products, such as proteins or non-coding RNA molecules, which ultimately contribute to an organism's observable traits or phenotype. The process of gene expression involves transcription, where the genetic information stored in DNA is transcribed into RNA molecules, and translation, where these RNA molecules are used as a template to synthesise proteins.
Transcription is performed by an enzyme called RNA polymerase, which recognises the specific site on the DNA molecule to initiate transcription. RNA polymerase adds nucleotides one at a time to create a complementary RNA strand. This process differs between bacteria and eukaryotes. In bacteria, the RNA polymerase has a detachable subunit called the sigma (σ) factor, which helps identify the starting point of transcription. In contrast, eukaryotic cells possess three types of RNA polymerases (I, II, and III), and the initiation of transcription involves the assembly of numerous proteins, including transcriptional activator proteins, at the start site.
The regulation of gene expression is crucial for cells to adapt to their environment, respond to external signals, repair damage, and maintain overall function. This regulation involves controlling the timing, location, and amount of gene products, such as proteins or non-coding RNAs. Constitutive genes are those that are transcribed continuously, in contrast to facultative genes, which are transcribed only when needed. Housekeeping genes, essential for basic cellular functions, are typically expressed in all cell types and are considered constitutively expressed.
The expression of constitutive genes can be influenced by various factors. For example, enhancer sequences can increase the rate of transcription by interacting with promoters, and this interaction is facilitated by activator proteins. Additionally, the strength of promoters and enhancers can impact gene expression, with alterations potentially leading to diseases such as cancer.
While constitutive gene expression provides a constant level of gene products, it may not always be the optimal strategy. In changing environments, adjusting gene expression levels to meet the demand for corresponding proteins can be challenging due to the slow response of protein level adjustments. Therefore, the choice between constitutive and responsive gene expression strategies depends on various factors, including environmental conditions, demand frequency, and genetic response rate.
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They are not influenced by transcription factors
Constitutive genes are those that are expressed following the interaction between a promoter and RNA polymerase. They are transcribed at a relatively constant level, and their expression is consistent enough to be used as a standard when comparing expression levels. The expression of these genes does not require a very special transcription factor, and biologists have not found an experimental condition that greatly impacts the expression level.
Transcription factors (TFs) are proteins that bind to specific DNA sequences and regulate gene expression. They play a crucial role in gene regulation by controlling the transcription of DNA into RNA. Each TF has a specific DNA-binding domain that recognizes a specific sequence of DNA bases, allowing it to bind to the DNA molecule. The binding of TFs to DNA can either activate or repress gene expression. They can act as activators by recruiting RNA polymerase to initiate transcription or as repressors by blocking the binding of RNA polymerase to the DNA.
The activity of TFs is regulated by various mechanisms, including intracellular signals that modify the TFs through processes such as phosphorylation, acetylation, or glycosylation. These modifications can influence the ability of TFs to bind to DNA and regulate gene expression. Additionally, the nuclear membrane in eukaryotes regulates TFs by controlling the duration of their presence in the nucleus through reversible changes in their structure and the binding of other proteins.
In the context of constitutive genes, it is important to note that their expression is relatively constant and does not require specific or special transcription factors. While TFs play a significant role in regulating gene expression for many genes, constitutive genes maintain their expression levels without relying heavily on specific TFs. This suggests that the expression of constitutive genes is less influenced by the presence or absence of particular TFs.
Furthermore, the expression of constitutive genes is not highly coordinated, and they exhibit uncorrelated transcription initiation. This indicates that the expression of these genes is not tightly regulated by specific transcription factors. Instead, constitutive genes are expressed at intermediate levels, providing an immediate benefit when the protein is needed. The expression of constitutive genes is influenced by environmental factors and the demand for the gene product, rather than being solely dependent on specific transcription factors.
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Constitutive genes are not regulated
Gene expression is the process by which information from a gene is used to synthesise a functional gene product, such as a protein, and ultimately affect a phenotype. The regulation of gene expression controls the timing, location, and amount of a given gene product present in a cell. This regulation is vital to give cells the flexibility to adapt to their environment, external signals, and other stimuli.
Constitutive genes are those that are transcribed continually, as opposed to facultative genes, which are only transcribed when needed. Constitutive genes are expressed following the interaction of a promoter and RNA polymerase without additional regulation. They are expressed at a level that doesn't seem to vary much across cells of the same type, and they do not require a special transcription factor.
Housekeeping genes, which are required to maintain basic cellular function, are typically constitutive genes. Examples include actin, GAPDH, and ubiquitin. These genes are transcribed at a relatively constant rate and can be used as a reference point in experiments to measure the expression rates of other genes.
While constitutive genes are not regulated in the same way as facultative genes, they are still subject to some degree of control. For example, the rate of translation and protein/mRNA degradation can influence protein levels. Additionally, the stability of the final gene product can impact expression levels—an unstable product results in a low expression level.
In summary, while constitutive genes may not be regulated in the traditional sense of having specific transcription factors or environmental triggers, they are still subject to certain mechanisms that modulate their expression levels.
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They are distinct from facultative genes
Genes that are constitutively expressed are distinct from facultative genes. Constitutive genes are always expressed and are usually essential for basic cellular function and survival. In contrast, facultative genes are only expressed under specific conditions or in certain cell types. They are often involved in specialised functions or responses to particular stimuli.
Facultative genes are typically regulated by specific transcription factors that activate their expression in response to particular signals or environmental cues. For example, a facultative gene might be turned on in response to a stressor or a change in the cellular environment. The protein product of a facultative gene might only be required in certain circumstances or at specific developmental stages.
The expression of facultative genes is often tightly controlled and may involve complex regulatory networks. These regulatory mechanisms can be very specific, ensuring that the gene is only expressed when needed. In contrast, constitutive genes are generally expressed at relatively constant levels and are not subject to the same level of complex regulation.
An example of a facultative gene is the heat shock protein (HSP) gene. HSPs are only expressed in response to stress, such as high temperatures, which can damage cellular proteins. In response to this stress, the HSP genes are activated, producing proteins that help protect and repair other proteins in the cell. Once the stress is removed, the expression of HSP genes is turned off again.
Another example is the insulin gene, which is only expressed in specific cells in the pancreas. The expression of this gene is regulated by a complex set of transcription factors that ensure it is only turned on in the correct cell type and in response to specific nutritional signals. The insulin gene is not constitutively expressed as it is only required to be active in certain cells and under certain physiological conditions.
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Frequently asked questions
A constitutively expressed gene is transcribed continually, as opposed to a facultative gene, which is only transcribed when needed. Constitutive genes are expressed following the interaction between a promoter and RNA polymerase without additional regulation.
A constitutively expressed gene is always transcribed, whereas a facultative gene is only transcribed when needed. An example of a facultative gene is one that is expressed in response to environmental changes.
Examples of constitutively expressed genes include housekeeping genes such as actin, GAPDH, and ubiquitin. Housekeeping genes are required to maintain basic cellular function and are typically expressed in all cell types of an organism.
