How different genes are expressed in different cell types. The big picture of eukaryotic gene regulation.
Key points:
Gene regulation is the process of controlling which genes in a cell's DNA are expressed (used to make a functional product such as a protein).
Different cells in a multicellular organism may express very different sets of genes, even though they contain the same DNA.
The set of genes expressed in a cell determines the set of proteins and functional RNAs it contains, giving it its unique properties.
In eukaryotes like humans, gene expression involves many steps, and gene regulation can occur at any of these steps. However, many genes are regulated primarily at the level of transcription.
Introduction
Your amazing body contains hundreds of different cell types, from immune cells to skin cells to neurons. Almost all of your cells contain the same set of DNA instructions – so why do they look so different, and do such different jobs? The answer: different gene regulation!
Gene regulation makes cells different
Gene regulation is how a cell controls which genes, out of the many genes in its genome, are "turned on" (expressed). Thanks to gene regulation, each cell type in your body has a different set of active genes – despite the fact that almost all the cells of your body contain the exact same DNA. These different patterns of gene expression cause your various cell types to have different sets of proteins, making each cell type uniquely specialized to do its job.
For example, one of the jobs of the liver is to remove toxic substances like alcohol from the bloodstream. To do this, liver cells express genes encoding subunits (pieces) of an enzyme called alcohol dehydrogenase. This enzyme breaks alcohol down into a non-toxic molecule. The neurons in a person's brain don’t remove toxins from the body, so they keep these genes unexpressed, or “turned off.” Similarly, the cells of the liver don’t send signals using neurotransmitters, so they keep neurotransmitter genes turned off.
Left panel: liver cell. The liver cell contains alcohol dehydrogenase proteins. If we look in the nucleus, we see that an alcohol dehydrogenase gene is expressed to make RNA, while a neurotransmitter gene is not. The RNA is processed and translated, which is why the alcohol dehydrogenase proteins are found in the cell. Right panel: neuron. The neuron contains neurotransmitter proteins. If we look in the nucleus, we see that the alcohol dehydrogenase gene is not expressed to make RNA, while the neurotransmitter gene is. The RNA is processed and translated, which is why the neurotransmitter proteins are found in the cell.
There are many other genes that are expressed differently between liver cells and neurons (or any two cell types in a multicellular organism like yourself).
How do cells "decide" which genes to turn on?
Now there's a tricky question! Many factors can affect which genes a cell expresses. Different cell types express different sets of genes, as we saw above. However, two different cells of the same type may also have different gene expression patterns depending on their environment and internal state.
Broadly speaking, we can say that a cell's gene expression pattern is determined by information from both inside and outside the cell.
Examples of information from
insidethe cell: the proteins it inherited from its mother cell, whether its DNA is damaged, and how much ATP it has.
Examples of information from
outsidethe cell: chemical signals from other cells, mechanical signals from the extracellular matrix, and nutrient levels.
How do these cues help a cell "decide" what genes to express? Cells don't make decisions in the sense that you or I would. Instead, they have molecular pathways that convert information – such as the binding of a chemical signal to its receptor – into a change in gene expression.
As an example, let's consider how cells respond to growth factors. A growth factor is a chemical signal from a neighboring cell that instructs a target cell to grow and divide. We could say that the cell "notices" the growth factor and "decides" to divide, but how do these processes actually occur?
Growth factors bind to their receptors on the cell surface and activate a signaling pathway in the cell. The signaling pathway activates transcription factors in the nucleus, which bind to DNA near division-promoting and growth-promoting genes and cause them to be transcribed into RNA. The RNA is processed and exported from the nucleus, then translated to make proteins that drive growth and division.
The cell detects the growth factor through physical binding of the growth factor to a receptor protein on the cell surface.
Binding of the growth factor causes the receptor to change shape, triggering a series of chemical events in the cell that activate proteins called transcription factors.
The transcription factors bind to certain sequences of DNA in the nucleus and cause transcription of cell division-related genes.
The products of these genes are various types of proteins that make the cell divide (drive cell growth and/or push the cell forward in the cell cycle).
This is just one example of how a cell can convert a source of information into a change in gene expression. There are many others, and understanding the logic of gene regulation is an area of ongoing research in biology today.
Growth factor signaling is complex and involves the activation of a variety of targets, including both transcription factors and non-transcription factor proteins. You can learn more about how growth factor signaling works in the article on intracellular signal transduction.
Eukaryotic gene expression can be regulated at many stages
In the articles that follow, we’ll examine different forms of eukaryotic gene regulation. That is, we'll see how the expression of genes in eukaryotes (like us!) can be controlled at various stages, from the availability of DNA to the production of mRNAs to the translation and processing of proteins.
Eukaryotic gene expression involves many steps, and almost all of them can be regulated. Different genes are regulated at different points, and it’s not uncommon for a gene (particularly an important or powerful one) to be regulated at multiple steps.
Chromatin accessibility. The structure of chromatin (DNA and its organizing proteins) can be regulated. More open or “relaxed” chromatin makes a gene more available for transcription.
Transcription. Transcription is a key regulatory point for many genes. Sets of transcription factor proteins bind to specific DNA sequences in or near a gene and promote or repress its transcription into an RNA.
RNA processing. Splicing, capping, and addition of a poly-A tail to an RNA molecule can be regulated, and so can exit from the nucleus. Different mRNAs may be made from the same pre-mRNA by alternative splicing.
Stages of eukaryotic gene expression (any of which can be potentially regulated). Chromatin structure. Chromatin may be tightly compacted or loose and open. Transcription. An available gene (with sufficiently open chromatin) is transcribed to make a primary transcript. Processing and export. The primary transcript is processed (spliced, capped, given a poly-A tail) and shipped out of the nucleus. mRNA stability. In the cytosol, the mRNA may be stable for long periods of time or may be quickly degraded (broken down). Translation. The mRNA may be translated more or less readily/frequently by ribosomes to make a polypeptide. Protein processing. The polypeptide may undergo various types of processing, including proteolytic cleavage (snipping off of amino acids) and addition of chemical modifications, such as phosphate groups. All these steps (if applicable) need to be executed for a given gene for an active protein to be present in the cell.
Image based on similar diagrams from Reece et al. 1start superscript, 1, end superscript and Purves et al. 2squared
RNA stability. The lifetime of an mRNA molecule in the cytosol affects how many proteins can be made from it. Small regulatory RNAs called miRNAs can bind to target mRNAs and cause them to be chopped up.
Translation. Translation of an mRNA may be increased or inhibited by regulators. For instance, miRNAs sometimes block translation of their target mRNAs (rather than causing them to be chopped up).
Protein activity. Proteins can undergo a variety of modifications, such as being chopped up or tagged with chemical groups. These modifications can be regulated and may affect the activity or behavior of the protein.
Although all stages of gene expression can be regulated, the main control point for many genes is transcription. Later stages of regulation often refine the gene expression patterns that are "roughed out" during transcription.
To learn more, see the articles on transcription factors and regulation after transcription.
Gene regulation and differences between species
Differences in gene regulation makes the different cell types in a multicellular organism (such as yourself) unique in structure and function. If we zoom out a step, gene regulation can also help us explain some of the differences in form and function between different species with relatively similar gene sequences.
For instance, humans and chimpanzees have genomes that are about 98.8%98, point, 8, percent identical at the DNA level. The protein-coding sequences of some genes are different between humans and chimpanzees, contributing to the differences between the species. However, researchers also think that changes in gene regulation play a major role in making humans and chimps different from one another. For instance, some DNA regions that are present in the chimpanzee genome but missing in the human genome contain known gene-regulatory sequences that control when, where, or how strongly a gene is expressed3cubed.
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FAQs
Overview: Eukaryotic gene regulation (article) | Khan Academy? ›
Unlike prokaryotic cells, eukaryotic cells can regulate gene expression at many different levels. Eukaryotic gene expression begins with control of access to the DNA. This form of regulation, called epigenetic regulation, occurs even before transcription is initiated.
What is the overview of eukaryotic gene regulation? ›Unlike prokaryotic cells, eukaryotic cells can regulate gene expression at many different levels. Eukaryotic gene expression begins with control of access to the DNA. This form of regulation, called epigenetic regulation, occurs even before transcription is initiated.
What is gene regulation answers? ›Gene regulation is the process of controlling which genes in a cell's DNA are expressed (used to make a functional product such as a protein). Different cells in a multicellular organism may express very different sets of genes, even though they contain the same DNA.
What are the 4 levels of gene regulation in eukaryotes? ›Gene expression is controlled at the epigenetic, transcriptional, post-transcriptional, translational, and post-translational levels in eukaryotic cells.
What is the overview of gene regulation in prokaryotes? ›Regulation of transcription in prokaryotes typically involves operons. An operon is a region ofDNA that consists of one or more genes that encode the proteins needed for a specific function. The operon also includes a promoter and an operator. The operator is a region of the operon where regulatory proteins bind.
Why is eukaryotic gene regulation important? ›The regulation of gene expression is extremely important during the development of an organism. Regulatory proteins must turn on certain genes in particular cells at just the right time so the organism develops normal organs and organ systems.
How are eukaryotic genes regulated at the DNA level? ›Eukaryotic gene expression is regulated during transcription and RNA processing, which take place in the nucleus, and during protein translation, which takes place in the cytoplasm. Further regulation may occur through post-translational modifications of proteins.
What was the purpose of gene regulation? ›Gene regulation is an important part of normal development. Genes are turned on and off in different patterns during development to make a brain cell look and act different from a liver cell or a muscle cell, for example. Gene regulation also allows cells to react quickly to changes in their environments.
What are the three types of gene regulation? ›All three domains of life use positive regulation (turning on gene expression), negative regulation (turning off gene expression), and co-regulation (turning multiple genes on or off together) to control gene expression, but there are some differences in the specifics of how these jobs are carried out between ...
What is a gene regulation quizlet? ›Gene Regulation. Refers to the ability of cells to control the expression of their genes. Cell Differentation. The process by which cells become specialized into particular types.
What are the 5 stages of gene regulation? ›
Regulation of gene expression can happen at any of the stages as DNA is transcribed into mRNA and mRNA is translated into protein. For convenience, regulation is divided into five levels: epigenetic, transcriptional, post-transcriptional, translational, and post-translational (Figure 17.6).
What are three factors involved in eukaryotic gene regulation? ›What are three mechanisms by which transcription factors regulate eukaryotic gene expression? Eukaryotic cells have three mechanisms that control transcription of genes - transcription factors, cell specialization, and RNA interference.
What is positive and negative gene regulation in eukaryotes? ›Positive vs Negative Gene Regulation
Positive gene regulation is a process which makes the genes express and synthesize proteins. Negative gene regulation is a process which represses gene expression. Positive control is done by activator or the transcription factor binding with the promoter region.
Gene expression in prokaryotes is mostly regulated at the transcriptional level (some epigenetic and post-translational regulation is also present), whereas in eukaryotic cells, gene expression is regulated at the epigenetic, transcriptional, post-transcriptional, translational, and post-translational levels.
What is the most common gene regulation in prokaryotes and eukaryotes? ›To regulate transcription, both prokaryotes and eukaryotes rely on proteins that act as either activators that “turn on” gene expression or repressors that “turn off” gene expression. Repressors are more common in prokaryotes than they are in eukaryotes.
What is the difference between prokaryotes and eukaryotes gene regulation? ›Prokaryotic gene expression is primarily controlled at the level of transcription. Eukaryotic gene expression is controlled at the levels of epigenetics, transcription, post-transcription, translation, and post-translation.
When can gene regulation occur in eukaryotic cells? ›Gene regulation can occur at any point of the transcription-translation process but most often occurs at the transcription level. Proteins that can be activated by other cells and signals from the environment are called transcription factors.
Why gene regulation is important in bacteria and eukaryotes? ›These examples illustrate an important point: that gene regulation allows bacteria to respond to changes in their environment by altering gene expression (and thus, changing the set of proteins present in the cell).
What is an example of a eukaryotic gene regulation? ›An example is the TATA box, so named because it has a core sequence of TATAAA. This is a regulatory element that is part of the promoter of most eukaryotic genes. A number of regulatory proteins bind to the TATA box, forming a multi-protein complex.
What are the characteristics of a eukaryotic gene? ›The structure of eukaryotic genes. Most eukaryotic genes contain segments of coding sequences (exons) interrupted by noncoding sequences (introns). Both exons and introns are transcribed to yield a long primary RNA transcript.
What is gene regulation theory? ›
Gene regulation involves a complex web of interactions within a given cell among signals from the cell's environment, signaling molecules within the cell, and the cell's DNA. These interactions lead to the expression of some genes and the suppression of others, depending on circumstances.
How is gene regulation controlled? ›Specifically, gene expression is controlled on two levels. First, transcription is controlled by limiting the amount of mRNA that is produced from a particular gene. The second level of control is through post-transcriptional events that regulate the translation of mRNA into proteins.
What are the methods of gene regulation? ›Regulation of gene expression is a complex process that can be controlled at several steps,including transcription, pre-mRNA splicing and export, mRNA stability, translation, protein modification, and protein half-life.
What is the most common form of gene regulation? ›transcriptional - level control. The most common form of gene expression regulation in both bacteria and eukaryotes is the transcriptional - level control.
What is the difference between gene expression and gene regulation? ›The key difference between gene expression and gene regulation is that gene expression is a process that produces a functional protein or RNA from the genetic information hidden in a gene while gene regulation is the process that induces or represses the expression of a gene.
What is gene regulation in cell cycle? ›Cell cycle-dependent gene transcription is tightly controlled by the retinoblastoma (RB):E2F and DREAM complexes, which repress all cell cycle genes during quiescence. Cyclin-dependent kinase (CDK) phosphorylation of RB and DREAM allows for the expression of two gene sets.
What are regulatory genes called? ›regulatory gene. noun. variants or regulator gene. : a gene that regulates the expression of one or more structural genes by controlling the production of a protein (as a genetic repressor) which regulates their rate of transcription.
What controls gene expression? ›Gene expression is primarily controlled at the level of transcription, largely as a result of binding of proteins to specific sites on DNA.
What is the difference between positive and negative gene regulation? ›Positive regulation is that regulation in which the presence of specific regulatory element increases the expression of genetic information quantitatively. Negative regulation is regulation in which the presence of specific regulatory elements diminishes the expression of genetic information.
What is an example of a regulatory gene? ›In the Operon Model, the regulatory genes are those that code for the production of regulatory proteins. For instance, the regulatory gene in lac operon is the lac I gene that codes for the lac repressor. The repressor protein binds to operator gene, which consequently prevents the production of a specific enzyme.
Why is gene regulation in eukaryotes more complex? ›
Gene regulation in eukaryotes is more complex than in prokaryotes. This is in part because their genomes are larger and because they encode more genes. For example, the E. coli genome houses about 5,000 genes, compared to around 25,000 genes in humans.
What is the role of the promoter in eukaryotic gene regulation? ›The purpose of the promoter is to bind transcription factors that control the initiation of transcription. Within the promoter region, just upstream of the transcriptional start site, resides the TATA box. This box is simply a repeat of thymine and adenine dinucleotides (literally, TATA repeats).
What are the 3 things that happen to a eukaryotic mRNA? ›- Capping at the 5' end.
- Addition of a poly(A) tail at the 3' end.
- Splicing to remove introns.
The trp operon is regulated by two mechanisms, negative corepression and attenuation. Most of the operons involved in amino acid synthesis are regulated by these two mechanisms. The trp operon is negatively controlled by the trp repressor, a product of the trpR gene.
What is an example of negative gene regulation? ›A classic example of negative repressible regulation of gene expression involves the trp operon, which is regulated by a negative feedback loop.
Does each gene have its own promoter in eukaryotes? ›Another difference is that eukaryotic genes are not clustered into operons controlled from a single promoter. Most genes encode only a single protein, and each gene has its own promoter.
Why do eukaryotes not have operons? ›Operons are a hallmark of bacterial genomes, where they allow concerted expression of functionally related genes as single polycistronic transcripts. They are rare in eukaryotes, where each gene usually drives expression of its own independent messenger RNAs.
What are methods of gene regulation found in eukaryotes but not prokaryotes? ›Prokaryotic transcription and translation occur simultaneously in the cytoplasm, and regulation occurs at the transcriptional level. Eukaryotic gene expression is regulated during transcription and RNA processing, which take place in the nucleus, and during protein translation, which takes place in the cytoplasm.
Is gene regulation in eukaryotes simpler than prokaryotes? ›Explanation: There are multiple ways gene regulation differs between prokaryotes and eukaryotes. Prokaryotics don't have a nucleus but eukaryotics do (see image below). So transcription and its regulation in prokaryotics is much simpler.
What is the main difference between eukaryotic and prokaryotic gene regulation quizlet? ›What is the main difference between eukaryotic and prokaryotic gene regulation? Groups of eukaryotic genes are likely to be regulated together, whereas each prokaryotic gene is usually regulated separately.
What is one way that gene regulation in eukaryotic and prokaryotic cells is similar? ›
One way that gene regulation in eukaryotic and prokaryotic cells is similar is: In both types of cell, the primary mechanism to regulate gene expression is at the level of transcriptional regulation.
Which explains a difference between prokaryotic and eukaryotic gene regulation quizlet? ›Eukaryotes regulate gene expression through the use of protein transcription factors whereas prokaryotes do not. Eukaryotes regulate gene expression primarily post-transcriptionally, whereas prokaryotes primarily regulate transcription.
What does gene regulation in eukaryotic cells include quizlet? ›Eucaryotic cells have three mechanisms that control transcription of genes - transcription factors, cell specialization, and RNA interference.
Which explains a difference between prokaryotic and eukaryotic gene regulation? ›Eukaryotic cells contain a nucleus whereas prokaryotes do not, and eukaryotes show greater compartmentalization that allows for greater regulation of gene expression. Prokaryotic cells are less complex and perform highly-regulated gene expression whereas eukaryotes perform less-regulated gene expression.
What is gene regulation more specific in eukaryotic organisms? ›Gene regulation in eukaryotes is more complex than in prokaryotes. This is in part because their genomes are larger and because they encode more genes. For example, the E. coli genome houses about 5,000 genes, compared to around 25,000 genes in humans.
What is eukaryotic regulation of translation? ›Eukaryotic mRNA translation is a very complicated process that consists of four major phases:initiation, elongation, termination and ribosome recycling, while the regulation takes place mainly at the initiation stage which is the rate-limiting step of protein synthesis among the four steps of translation [1].
Where does gene regulation occur in eukaryotic cells? ›In eukaryotic cells, the first stage of gene expression control occurs at the epigenetic level. Epigenetic mechanisms control access to the chromosomal region to allow genes to be turned on or off.
What are three things gene regulation allows cells to do? ›transcriptional control (whether and how much a gene is transcribed into mRNA) translational control (whether and how much an mRNA is translated into protein) post-translational control (whether the protein is in an active or inactive form, and whether the protein is stable or degraded)
What is the purpose of gene regulation? ›Gene regulation is an important part of normal development. Genes are turned on and off in different patterns during development to make a brain cell look and act different from a liver cell or a muscle cell, for example. Gene regulation also allows cells to react quickly to changes in their environments.
What is the most common method of gene regulation in both prokaryotes and eukaryotes? ›Sequence-specific transcription factors are considered the most important and diverse mechanisms of gene regulation in both prokaryotic and eukaryotic cells (Pulverer, 2005).
Which is the most common form of gene expression regulation in eukaryotic cells? ›
The most common form of gene expression regulation in both bacteria and eukaryotes is the transcriptional - level control.