Gene Regulation and the Order of the Operon (2023)


Explore gene expression with the Amoeba Sisters, including the fascinating Lac Operon found in bacteria! Learn how genes can be turned "on" and "off" and why this is essential for cellular function. Check out our FREE video handouts on!

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The Amoeba Sisters videos demystify science with humor and relevance. The videos center on Pinky's certification and experience in teaching biology at the high school level. For more information about The Amoeba Sisters, visit:

We cover the basics in biology concepts at the secondary level. If you are looking to discover more about biology and go into depth beyond these basics, our recommended reference is the FREE, peer reviewed, open source OpenStax biology textbook:

*Further Reading*
As our pinned comment mentions, we cover basics with the goal of inspiring curiosity for more! There are so many important details to explore. For example, the conversion of lactose to allolactose, the cAMP-CAP conversion that stimulates the RNA polymerase, or the names of the different genes and their individual functions. We also don't mention that there are other factors that can affect the activation of this operon (such as glucose levels). Check out this further reading suggestion in OpenStax Microbiology to learn more:


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You ever thought about how disastrous it could be if the cells in your eyes started producing the same hydrochloric acid that is made by your stomach cells? Your stomach cells produce HCL to help break down food, but you definitely don’t want that in your eyes.

Thank, goodness that doesn’t happen! But it’s surprising---because, both your eye cells and stomach cells contain all of your DNA.

All of your DNA is found in your body cells, but see---the portions that are used need to be regulated.



We could end up with something ridiculous.

Like…Eye cells producing digestive enzymes.

And that wouldn’t just be a waste of resources---that, would actually be very difficult to explain to your friends.You want some genes to be regulated.


Remember that genes are made up of DNA.

Dna is used to give instructions for the production of proteins in the process of protein synthesis.


An important concept is that there needs to be a method of determining which genes will be turned on and which genes will be turned.


This is called gene regulation.

There are many ways that genes are regulated., In, your human body cells.

You can have proteins that can bind to certain gene regions to increase the rate of transcription for the transcription enzyme, RNA polymerase.


You can have proteins decrease transcription to the point that it may not be transcribed at all.

That is a form of gene regulation., Your eye cells.

Don’t use the portion of DNA that codes for making HCL like your stomach cells do, because there is regulation like this in all of your cells to determine which portions of DNA is used.


We want to shift gears now to talk about a very interesting way of regulating genes that can sometimes be challenging to visualize.

A way that has not been found in humans, but instead is found in prokaryotes----with a few eukaryote exceptions.

It’s called an operon.

An operon is a fancy way of regulating genes and it usually is made up of a few genes that involve enzymes.

Remember, that enzymes are proteins with the ability to break down or build up the substances that they act.


Let’s talk about some key players in an operon, so we can see some gene regulation., First, RNA, polymerase., It’s, a builder- a builder enzyme, actually because RNA polymerase is an enzyme.

Remember that many things in biology that end in that –ase are enzymes.

Rna polymerase is needed in order to start transcription.


That transcription and translation are steps in protein synthesis.

Protein synthesis, which means to make proteins---enzymes in this case.

The thing about RNA polymerase though---it gets a little confusing for RNA polymerase.

Without somewhere to bind.


You watched our DNA replication video, you learned about DNA polymerase and how it needs to have a primer to know where to start.

Well, RNA Polymerase needs a promoter.

A promoter is a sequence of DNA.

Where RNA polymerase can bind to.


You would think that’s it---you get RNA polymerase attached to a promoter and boom! You make your mRNA, which eventually will be used to make a protein right? But there’s, this other sequence of DNA called an operator.

The operator, is a part of the DNA where something called a repressor can bind.

The big bad repressor, if bound to the operator, blocks.

Rna polymerase., Poor, RNA polymerase cannot move forward and no mRNA can be made.

Therefore, no proteins.

So take a look at our setup.


This is an example called a Lac Operon.


There is a promoter region of the DNA, the operator region of the DNA, and these are three genes: {have labeled, lacZ, lacY, and lacA).

That code for enzymes that help in the process of breaking down lactose.

Lactose is a sugar.

If lactose sugar is around.

Bacteria want these enzymes to be made, so they can use them to break down the lactose sugar.

Then they can metabolize it! Fed bacteria are happy.


Here’s, the repressor.


Actually, a gene here on the operon that codes for producing the repressor.


This gene that we call “I”? It has its own promoter.

This codes for the production of the repressor.


Why do we need this repressor? Well, it’s wasteful to make things that you don’t need., If there’s, no lactose,? It wouldn’t make sense to start making enzymes that work together to break down lactose.

It would be a waste---the.

Enzymes would just sit there.


If lactose is not present, then the repressor binds to the operator.

This blocks.

Rna polymerase.

mRNA cannot be made.


Therefore, the proteins---enzymes in this case---cannot be made.


If lactose is around in the environment, something pretty cool, happens.

The lactose---remember, that’s the sugar, binds to the repressor.

This changes the repressor’s conformation.

Try, as it might----the repressor can’t bind to the operator.

RNA polymerase finds its promoter, binds, and transcribes to make mRNA from the genes on the operon.

That mRNA will be used to make enzymes to break down that lactose sugar.

Bacteria like to eat so…that makes them pretty happy.

We have to say that we think it is pretty impressive to think about all the gene regulation that goes on in cells---and.

If you find it fascinating---know that there are careers that focus on gene regulation., By understanding how genes can be turned on and off, we can also gain a better understanding of treating a variety of diseases that have gene influences in the human body.

Well, that’s it for the amoeba sisters, and we remind you to stay curious!.


What is the correct order of genes in an operon? ›

1: RNA Polymerase, 2: Repressor, 3: Promoter, 4: Operator, 5: Lactose, 6: lacZ, 7: lacY, 8: lacA. Top: The gene is essentially turned off. There is no lactose to inhibit the repressor, so the repressor binds to the operator, which obstructs the RNA polymerase from binding to the promoter and making lactase.

What is gene regulation answers? ›

Gene regulation is the process used to control the timing, location and amount in which genes are expressed. The process can be complicated and is carried out by a variety of mechanisms, including through regulatory proteins and chemical modification of DNA.

How is gene regulated via operon system? ›

operon, genetic regulatory system found in bacteria and their viruses in which genes coding for functionally related proteins are clustered along the DNA. This feature allows protein synthesis to be controlled coordinately in response to the needs of the cell.

What is the gene regulation for the lac operon? ›

In lac operon, lactose acts as an inducer. If lactose is provided in the medium for the bacteria, the regulatory gene is activated. The inducer will bind to the repressor protein and render it inactive which allows transcription of the operon. Thus, the lac operon is negatively regulated in this case.

What is the correct order of the steps of gene expression? ›

Information from a gene is used to build a functional product in a process called gene expression. A gene that encodes a polypeptide is expressed in two steps. In this process, information flows from DNA → RNA → protein, a directional relationship known as the central dogma of molecular biology.

What is the process of gene regulation? ›

Gene regulation can occur at any point during gene expression, but most commonly occurs at the level of transcription (when the information in a gene's DNA is passed to mRNA). Signals from the environment or from other cells activate proteins called transcription factors.

What is a summary of gene expression and regulation? ›

Gene expression be thought of as an “on/off switch” to control when and where RNA molecules and proteins are made and as a “volume control” to determine how much of those products are made. The process of gene expression is carefully regulated, changing substantially under different conditions and cell types.

How many genes are contained within the operon? ›

The DNA of the operon contains three genes, Gene 1, Gene 2, and Gene 3, which are found in a row in the DNA. They are under control of a single promoter (site where RNA polymerase binds) and they are transcribed together to make a single mRNA that has contains sequences coding for all three genes.

What is gene regulation in cell cycle? ›

The cell cycle is regulated by genes encoding products (i.e., enzymes and proteins) that play crucial roles in the maintenance of an orderly sequence of events that ensures that each resultant daughter cell will inherit the same amount of genetic information.

What are the three levels of gene regulation? ›

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 relationship between a gene and an operon? ›

Expression of a Gene Increases As Its Position Moves Proximally Within an Operon. Within an operon, the transcription distance of a gene increases as its position moves away from the end of the operon.

What is an example of an operon? ›

The best-studied examples of operons are from the bacterium Escherichia coli (E. coli), and they involve the enzymes of lactose metabolism and tryptophan biosynthesis. Because the lactose (lac) operon shares many features with other operons, its organization and regulation are described in detail below.

What is the structure of the operon? ›

Operon Structure

Operons are regions of DNA that contain clusters of related genes. They are made up of a promoter region, an operator, and multiple related genes. The operator can be located either within the promoter or between the promoter and the genes.

How many genes are regulated by lac operon? ›

The lac operon contains three genes: lacZ, lacY, and lacA. These genes are transcribed as a single mRNA, under control of one promoter.

What is the first control sequence in an operon? ›

The operon discussed here is the lac operon, for "lactose." The first control sequence, the promoter, is the site where RNA polymerase attaches to the DNA. (Recall that RNA polymerase transcribes genes by making mRNA.) Between the promoter and the enzyme genes is a second control sequence called the operator.

Does each gene in an operon have a start codon? ›

Operons encoding genes to be translated contain one or more start codons and ribosome binding sites (often known as Shine–Dalgarno sequences).

What are genes in an operon quizlet? ›

Genes within an operon: Tend to be regulated by a common regulatory mechanism. Are generally involved in the same biochemical pathway. Are expressed as a polycistronic RNA.

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