Learning objectives
- Describe the role of the protein:DNA interaction in the regulation of transcription initiation in prokaryotes and eukaryotes
- Distinguish positive regulation from negative regulation
- Identify similarities and differences in gene regulation in prokaryotes and eukaryotes, including mechanisms of gene co-regulation, chromatin presence in eukaryotes and post-transcriptional regulation in eukaryotes
- Use a model gene regulatory system such as the lac operon to predict the effects of mutations in various components
Cells express (trancribe and translate) only part of their genes. Cells respond to environmental cues by turning on or off the expression of appropriate genes. In multicellular organisms, cells in various tissues and organsdistinguishor specialize in making different sets of proteins, even though all cells in the body (with a few exceptions) share the same genome. Such changes in gene expression, ordifferential gene expressionbetween cells are often regulated at the transcriptional level.
There are three broad levels of regulation of gene expression:
- transcription control (whether and to what extent a gene is transcribed into mRNA)
- translation control (whether and how much 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)
Based on our shared evolutionary ancestry, there are many similarities in the way prokaryotes and eukaryotes regulate gene expression.Tand there are many differences here.All three domains of life use upregulation (turning gene expression on), downregulation (turning gene expression off), and co-regulation (turning multiple genes on or off together) to control gene expression., but there are some differences in the specificity of performing these tasks between prokaryotes and eukaryotes.
Similarities between prokaryotes and eukaryotes: promoters and regulatory elements
prosecutorsare places in DNA where RNA polymerase attaches, initiating transcription. Promoters also contain or have binding sites close to each othertranscription factors, which are DNA-binding proteins that can help recruit or repel RNA polymerase. ANDadjusting elementit is a DNA sequence that certain transcription factors recognize and bind to recruit or reject RNA polymerase. The promoter and nearby transcription factor binding elements regulate gene transcription.
Regulatory elements can be used in both casespositiveminegativetranscription control. When a gene is under positive control of transcription, the binding of a particular transcription factor to a regulatory element promotes transcription. When a gene is under negative transcription control, a specific transcription factor binds to a regulatory elementSsuppress transcription. A single gene can be under positive and negative control of transcription by different transcription factors, creating multiple layers of regulation.
Some genes are not regulated: they areconstitutivelyexpress, that is, they are always transcribed. What genes should a cell always have?“eye,“whatever the environment or situation?
Differences between prokaryotes and eukaryotes: mechanisms of co-regulation
Often, a set of proteins is required together to respond to a specific stimulus or perform a specific function (e.g. multiple metabolic pathways). Often there are mechanisms to co-regulate these genes so that they are all transcribed in response to the same stimulus.Both prokaryotic and eukaryotic cells have ways of co-regulating genesbut they use very different mechanisms to achieve this goal.
In prokaryotes, co-regulated genes are usually organized in aoperonwhere two or more functionally related genes are transcribed together from a single promoter into a long mRNA. This mRNA is translated to produce all the proteins encoded by the genes in the operon. Ribosomes start at the 5' end, start translation at the first AUG codon, stop when they encounter a stop codon, and then start translation at the next AUG codon.
General operon in prokaryotes. R = regulatory protein (transcription factor); P = promoter; Pol = RNA polymerase
With a few exceptions (C. eleganceand related nematodes), eukaryotic genomes do not have genes arranged in operons. Instead, eukaryotic genes that are co-regulated tend to have the same sequence of DNA regulatory elements associated with each gene, even though these genes are on completely different chromosomes. This means that the same transcriptional activator or repressor can regulate the transcription of any gene to which that specific DNA regulatory element is associated. For example, eukaryotic HSP (heat shock protein) genes are located on different chromosomes. HSPs help cells survive and recover from heat shock (a type of cellular stress). All HSP genes are transcribed simultaneously in response to heat stress,because they all have a corresponding DNA sequence element that binds to the heat shock response transcription factor.
Additional complexities specific to eukaryotic gene regulation: chromatin and alternative splicing
Another important difference between prokaryotic gene regulation and eukaryotic gene regulation is that the double helix of eukaryotic (but not prokaryotic) DNA is organized around proteins calledtissuewhere DNA is organizednucleosomes. This combination of DNA + histone is calledchromatyna.
Chromatin can be condensed into a formation of 30 nm filaments (tightly packed nucleosomes) or loosely arranged as "balls on a string" where DNA between and around nucleosomes is more accessible. The degree of compaction is controlled by post-translational modifications added to the histones in the nucleosomes. When acetyl groups are added to histones by enzymes called histone acetyltransferases (HATs), the acetyl groups physically prevent nucleosomes from packing too tightly and help recruit other enzymes that further open up the chromatin structure. On the other hand, when the acetyl groups are removed by histone deacetylases (HDACs), the chromatin adopts a condensed formation that prevents transcription factors from accessing the DNA. In the image below, you can clearly see how much more compact and inaccessible the 30 nm fiber (top) compared to the stitch on the thread (bottom).
Chromatin plays a key role in regulating genes up and down,because transcription activators and RNA polymerase cannot physically access DNA regulatory elements when chromatin is in compact form.
Prokaryotic DNA has some associated proteins that help organize genomes, but it is fundamentally different from chromatin. Prokaryotic DNA can be considered essentially "naked" compared to eukaryotic chromatin, so prokaryotic cells lack this layer of gene regulation.
Another difference between the regulation of prokaryotic and eukaryotic genes is that eukaryotic mRNAs must be properly processed with 5' cap addition, intron splicing, and 3' poly(A) tail addition (discussed in more detail).Here). Each of these processing steps is also regulated, and the mRNA will degrade if any of them are not completed properly. The export of mRNA from the nucleus to the cytoplasm and the stability of properly processed mRNA in the cytoplasm are also regulated.
Finally, eukaryotic genes often have splice variants where different exons may be contained in different mRNAs that are transcribed from the same gene. Here you can see a drawing of a gene with color-coded exons and two different mRNA molecules transcribed from that gene. Different mRNAs encode different proteins because they contain different exons. This process is calledalternative connection,and let's talk about it furtherHere.
Often, different cell types in different tissues express different splice variants of the same gene, so that there is a heart-specific transcript and a kidney-specific transcript for a given gene.
In general, the regulation of eukaryotic genes is more complex than the regulation of prokaryotic genes. The upstream regulatory regions of eukaryotic genes have binding sites for many transcription factors, positive and negative regulators, which work in conjunction to determine the level of transcription. Some transcription factor binding sites, called enhancers and silencers, act thousands of base pairs away from the promoter. Activators are examples of upregulation and repressors are examples of downregulation.
Beginning of eukaryotic transcription, from biology.kenyon.edu (after Tjian)
General differences and similarities
If you understand the similarities and differences between eukaryotic and prokaryotic gene regulation, you will know which of the following processes are unique to eukaryotes, which are unique to prokaryotes, which occur in both, and how each is carried out:
- coupled transcription and translation
- tampa 5' i ogon poli(A) 3'
- AUG as the translation initiation codon
- regulation of gene expression by proteins binding regulatory DNA elements
- mRNA alternative splicing
- regulation of gene expression through chromatin accessibility
All together:tiredact inE coli
OtiredThe operon is goodmodel for understanding gene regulation. You should use the information below to ensure that you can apply all the gene regulation details described above to your specific example.
E colitiredoperon: double positive and negative regulation
lacI is the gene encoding the lac repressor protein; CAP = catabolite activating protein; O = operator; P = promoter; lacZ = gene encoding beta-galactosidase; lacY encodes permease; lacA encodes a transacetylase. Source: Wikimedia Commons (https://commons.wikimedia.org/wiki/File:Lac_operan-2010-21-01.png)
OtiredoperatorE colihas 3 structural genes necessary for the metabolism of lactose, a disaccharide found in large amounts in milk:
- lacZ encodes the enzyme beta-galactosidase, which cleaves lactose into glucose and galactose
- lacY encodes permease, a membrane protein that facilitates the diffusion of lactose into the cell
- lacA encodes transacetylase, an enzyme that modifies lactose
The mRNA encoding all 3 proteins is transcribed at high levels only when lactose is present and glucose is absent.
Negative regulation by repressors— In the absence of lactose, the lac Repressor protein, encoded bylacIa gene with a separate promoter that is always turned on binds to an operator sequence in the DNA. An operator sequence is a type of DNA regulatory element as described above. The operator-bound repressor protein prevents the initiation of transcription by RNA polymerase.
When lactose is present, the lactose-derived inducer molecule allosterically binds to the repressor and causes the repressor to leave the operator site. The RNA polymerase can then begin transcription if it successfully binds to itopromotor c.
Positive ZPP regulation— Glucose is the preferred substrate for energy metabolism. When glucose is present, cells rewritetiredoperon only at a very low level, so cells get most of their energy from glucose metabolism. RNA polymerase itself binds rather weaklytiredDistrict Attorney.
The lack of glucose causes an increase in the level of cyclic adenosine monophosphate (cAMP), which is an intracellular alarm signal. Cyclic AMP binds to the catabolism activator protein (CAP). The CAP+cAMP complex binds to a nearby CAP binding sitetiredpromoter and recruits RNA polymerase to the promoter.
The high level of transcription of the lac operon requires that CAP+cAMP be bound to the CAP binding site and that the repressor be absent in the operator. These conditions usually occur only in the absence of glucose and in the presence of lactose.
Otiredact inE coliis a classic example of a prokaryotic operon that is up- and down-regulated. Up and down regulation are universal topics of gene regulation in prokaryotes and eukaryotes.
FAQs
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 principles of gene regulation? ›The results revealed two design principles that make regulation of gene expression insulated from concentrations of shared machineries: RNA polymerase activity is fine-tuned to match translational output, and translational characteristics are similar across most messenger RNAs (mRNAs).
What kind of problems is Gurt intended to solve? ›GURT was developed to help prevent GM plants, such as the rice at left, from breeding with nonGM plants, such as the rice at right, when the GM rice is planted in fields.
What does it mean when we say a gene is turned off? ›These sequences hold directions for making the proteins that will carry out a cell's particular function. This is how one cell might end up being important to your kidneys, while another cell makes bone. When a gene is turned off, it no longer provides the directions for making proteins.
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 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 ...
How can we prevent GMO contamination? ›By agreeing with your neighbor to keep GMO crops in fields as far removed from your organic fields as possible, much of the risk of contamination can be reduced. Conventional farmers growing Bt crops are required to plant 20% of their acreage in non-Bt crops, to reduce the build-up of Bt-resistant insects.
Why is it important to maintain genetic diversity? ›Maintaining high genetic diversity allows species to adapt to future environmental changes and avoid inbreeding. Inbreeding, which happens when there are small, isolated populations, can reduce a species' ability to survive and reproduce.
How can we prevent genetically modified crops? ›Eat organic produce
Organic certification requires that no GM products are grown. So eating organic food ensures you are avoiding genetically modified food.
They found evidence that trauma can be passed between generations epigenetically, which means that trauma experienced by an ancestor might affect the way your genes are expressed. Bale's extensive work shows that parental stress can impact the following factors in children: risk for obesity. risk for diabetes.
Can humans turn genes on and off? ›
Epigenetics allows the muscle cell to turn “on” genes to make proteins important for its job and turn “off” genes important for a nerve cell's job. Your epigenetics change throughout your life. Your epigenetics at birth is not the same as your epigenetics during childhood or adulthood.
Can DNA be changed after birth? ›Structural changes can occur during the formation of egg or sperm cells, in early fetal development, or in any cell after birth. Pieces of DNA can be rearranged within one chromosome or transferred between two or more chromosomes.
What is the most common gene regulation? ›Sequence-specific transcription factors are considered the most important and diverse mechanisms of gene regulation in both prokaryotic and eukaryotic cells (Pulverer, 2005).
Why is gene regulation so important? ›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 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 is gene regulation also known as? ›Regulation of Gene Expression
Gene expression is the process by which the instructions present in our DNA are converted into a functional product, such as a protein. This process is a tightly coordinated process which allows a cell to respond to its changing environment.
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 is the difference between 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 are the 4 stages of gene regulation? ›Control of gene expression in eukaryotic cells occurs at epigenetic, transcriptional, post-transcriptional, translational, and post-translational levels.
What are 3 factors that can affect gene regulation? ›The internal factors that can affect gene expression are:- hormones, metabolic products, and gender. The external factors that affect gene expression are chemicals, temperature, and light.
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 should we stop using GMOs? ›ENVIRONMENTAL RISK
Cross-pollination creates herbicide-resistant “super weeds” that threaten other crops and wild plants. Tampering with crops' genetic makeup impacts down the food chain: scientists say GMO's have decimated butterfly populations in the United States, or led to birth defects among other animals.
GMO developer submits food safety assessment data and information to FDA. FDA evaluates the data and information and resolves any issues with the developer. Consultation is complete once FDA has no more questions about the safety of the human and animal food made from the new GMO plant variety.
What species have high genetic diversity? ›Bacteria and viruses tend to have very high genetic diversity, Cutter said. But it's hard to make an apples-to-apples comparison of genetic diversity between bacteria and viruses on one hand, and eukaryotes on the other, because species are defined differently in those categories, Cutter said.
What are some examples of genetic variation in humans? ›A person's skin color, hair color, dimples, freckles, and blood type are all examples of genetic variations that can occur in a human population.
What is an example of low genetic diversity? ›Low genetic diversity often occurs due to habitat loss. For example, when a species' habitat is destroyed or broken up into small pieces, populations become small.
What foods are not GMO in USA? ›Shop at farmer's markets and remember that most produce is safe non GMO, even conventional varieties, with the exception of corn, radicchio, beets, Hawaiian papaya, zucchini and yellow summer squash. Organic whole grains, legumes, nuts and seeds are safe.
How do GMOs affect human health? ›Do GMOs affect your health? GMO foods are as healthful and safe to eat as their non-GMO counterparts. Some GMO plants have actually been modified to improve their nutritional value. An example is GMO soybeans with healthier oils that can be used to replace oils that contain trans fats.
What are the pros and cons of genetic modification? ›The pros of GMO crops are that they may contain more nutrients, are grown with fewer pesticides, and are usually cheaper than their non-GMO counterparts. The cons of GMO foods are that they may cause allergic reactions because of their altered DNA and they may increase antibiotic resistance.
Can emotional trauma change your DNA? ›Here's how: Trauma can leave a chemical mark on a person's genes, which can then be passed down to future generations. This mark doesn't cause a genetic mutation, but it does alter the mechanism by which the gene is expressed. This alteration is not genetic, but epigenetic. We spoke with Dr.
Is anxiety inherited from mother or father? ›
Children with generalized anxiety disorder are 3.5 times more likely to have a mother with generalized anxiety disorder. Children with social anxiety disorder are almost 3 times more likely to have a father with anxiety disorder.
Is anxiety a genetic trait? ›There's clear research showing that anxiety is influenced by genetics. In fact, experts noticed a family connection for anxiety even before they understood how DNA or genes worked. If you have a close relative with anxiety, your chance of developing it's about 2 to 6 times higher than if you don't.
What happens if I tell gene to leave high on life? ›If the player tells Gene to leave, he threatens to take his bounty hunting equipment with him before affirming that it is clear he is still needed even if he isn't wanted. Either way, Gene stays. The only change is the dialogue that will come from the decision.
How do you deactivate a gene? ›One of the ways by which a cell turns off specific genes is by the reversible addition to the DNA of a minuscule chemical called a methyl group at the precise location of that specific gene.
Can genes be manipulated in humans? ›Human genome editing technologies can be used on somatic cells (non-heritable), germline cells (not for reproduction) and germline cells (for reproduction). Application of somatic human genome editing has already been undertaken, including in vivo editing, to address HIV and sickle-cell disease, for example.
Do you carry your baby daddy's DNA for 7 years? ›Male fetal progenitor cells persist in maternal blood for as long as 27 years postpartum. Division of Genetics, Children's Hospital, Boston, MA, USA.
How rare is a chimera human? ›They have genetic differences, but you could never guess someone is a chimera just by looking at them. The form of chimerism that Fairchild had is very rare; only about 100 cases have been recorded in human history. That might be because no one knew to look for it, though.
Can DNA be changed from male to female? ›Genetics overall cannot be changed (so far, at least)
Sex chromosomes, in particular, determine whether someone will have female or male body parts. As you can see in the image below, these are chromosomes found in a typical person.
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 does regulatory gene mean? ›Regulatory genes are those genes that code for proteins or factors that control the expression of structural genes. Location. In prokaryotes, the structural genes of related functionality are usually present adjacent to each other and regulated by a single promoter and operator.
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 are the two types of regulatory genes? ›Regulatory genes can also be described as positive or negative regulators, based on the environmental conditions that surround the cell. Positive regulators are regulatory elements that permit RNA polymerase binding to the promoter region, thus allowing transcription to occur.
What do regulatory genes produce? ›genetic regulation
operon is controlled by a regulator gene, which produces a small protein molecule called a repressor.
Regulatory elements are found at transcriptional and post-transcriptional levels and further enable molecular networks at those levels. For example, at the post-transcriptional level, the biochemical signals controlling mRNA stability, translation and subcellular localization are processed by regulatory elements.
What is the function of regulatory DNA? ›Regulatory DNA sequences also encode important functions—they control when, where, and how much genes are expressed. They do this by encoding "landing pads," i.e., binding sites for transcription factor proteins. Transcription factors then recruit the molecular machinery that transcribes a gene.
Why is regulation important in biology? ›Biological regulation is what allows an organism to handle the effects of a perturbation, modulating its own constitutive dynamics in response to particular changes in internal and external conditions.
Why does the gene expression need to be regulated? ›Gene expression is regulated to ensure that the correct proteins are made when and where they are needed. Regulation may occur at any point in the expression of a gene, from the start of the transcription phase of protein synthesis to the processing of a protein after synthesis occurs.
What is meant by positive gene regulation with example? ›In this type of gene regulation, the genes remain unexpressed until they are induced to express, thus called inducible gene expression. The inducer molecules are involved in inducing the expression of genes.
What happens if genes are not regulated? ›The control of gene expression is extremely complex. Malfunctions in this process are detrimental to the cell and can lead to the development of many diseases, including cancer.