Gene Regulation: Definition, Prokaryotes & Eukaryotes

Gene regulation is an important mechanism that controls protein biosynthesis. All living beings must regulate genes so that their cell(s) make just the right amount of the proteins they need. It enables organisms to respond to environmental changes and thus be more adaptable.

Gene regulation – definition

Under gene regulation refers to the regulation of the activity of genes. Gene expression can be understood as a synonym of gene regulation.

Gene regulation is an important mechanism that decides when to read genes. But why do genes have to be regulated at all??

Protein biosynthesis is roughly divided into the transcription of DNA into RNA (transcription) and the translation of RNA into an amino acid sequence on the ribosomes. A protein is then folded from the amino acid sequence.

Genes code for proteins. However, not all proteins are always needed in the cell. The different cells have different functions, which is why an immune cell, for example, needs different enzymes than a muscle cell to carry out its task. On the other hand, certain proteins are only required in special situations, such as for cell division. For energetic reasons, it therefore makes sense to regulate the synthesis of proteins.

Gene regulation allows genes to be switched on or off as needed. Genes that are not constantly active are called regulated genes. On the other hand, genes that are always active are constitutive genes designated. Gene regulation can be controlled in different ways in prokaryotes and eukaryotes.

Gene regulation in prokaryotes and eukaryotes

Since gene regulation can be controlled at different levels in prokaryotes and eukaryotes, a distinction is made between the groups of organisms. In general, eukaryotic cells are more complex and the transcription process takes place in the nucleus. Therefore, transcription and translation in eukaryotes are spatially and temporally separated. This results in more regulation possibilities in eukaryotic cells than in prokaryotic cells.

Gene regulation in prokaryotes

Scientists Francois Jacob and Jacques Monod discovered that the genes of prokaryotes in functional units are divided. Namely in so-called operons. Therefore, one speaks of the so-called gene regulation of prokaryotes operon model.

The operon model

An operon is therefore a DNA section that is also understood as a functional unit. An operon consists of promoterto the operator and several structural genes. In addition, the regulator gene, which codes for a so-called repressor, is located in front of the operon.

Of the promoter is the starting point for the transcription on the DNA while the operator acts as a binding site for the repressor. A repressor is a protein that, by binding to the operator, blocks the transcription of structural genes. structural genes are genes that code for proteins.

In addition, the regulator gene, which codes for a so-called repressor, is located in front of the operon.

Figure 1: Schematic representation of an operon Source: wikipedia.de.

The operon model distinguishes between two types of gene regulation, which you will get to know in the following chapters.

Gene regulation by substrate induction

In gene regulation by substrate induction, the repressor is inactivated by a substrate. This triggers the transcription of certain structural genes since the repressor can no longer bind to the operator. Gene regulation by substrate induction is also often understood as «positive gene regulation».

A substrate is a substance that is converted by an enzyme by binding to the enzyme using the key-lock principle.

An example of gene regulation by substrate induction is the degradation of lactose by E. coli-Bacteria. Here, lactose is the substrate. If the bacteria are in an environment that does not contain lactose, the structural genes will not be read because the repressor can still bind to the operator.

However, as soon as lactose is present in the culture medium, it binds to the repressor in the bacterial cell so that it can no longer bind to the operator. Thus, lactose itself stimulates the synthesis of certain enzymes to break it down. The lactose is therefore also understood as an inducer.

In general, this is an enzyme induction. The inducer is to be understood as an active ingredient that stimulates enzyme production. As an inducer, lactose is responsible for increasing the concentration of the enzyme lactase.

Figure 2: The Lac operon Source: wikipedia.de.

Gene regulation through end product repression

In gene regulation by end product repression, the end product activates a repressor and thus suppresses the transcription of the structural genes.

An example of gene regulation through end product repression is tryptophan synthesis E. coli-Bacteria. The structural genes of the tryptophan operon code for enzymes that are necessary for the synthesis of the amino acid tryptophan. The more tryptophan is produced, the more the synthesis of these enzymes is suppressed, because tryptophan itself first activates the repressor.

Figure 3: Example of end product repression Source: wikipedia.de.

The end product of the reactions, tryptophan, thus suppresses the synthesis of the enzymes needed to make it. In principle, structural, regulatory and operator genes have the same function in end product repression as in substrate induction. The difference is that the repressor is initially inactive.

It is only activated when it is combined with tryptophan and can attach itself to the operator. It inhibits the transcription of structural genes. If the concentration of tryptophan in the cell falls, the repressor and tryptophan separate and transcription can take place again.

Gene regulation in eukaryotes

In eukaryotes, gene regulation can occur at different levels and in many ways. Gene regulation serves in particular to control the development of a cell. For this it is important that the right proteins are produced at the right time, which are needed for development.

First, genes can transcription of the complementary RNA strand to the codogenic DNA strand. Affect at this stage of protein biosynthesis transcription factors the transcription of genes. More precisely, it is about enhancers and silencer. While enhancers increase the rate of transcription, silencers reduce the transcription of the gene.

After transcription can be done at the level of processing gene regulation also takes place in the RNA. With alternative splicing, attention can again be paid to which proteins are currently needed in the cell. This is because most human genes can be translated into more than one gene product in the subsequent translation.

In alternative splicing, the non-coding areas are cut out so that the coding areas are cut together. It is also possible to cut out sequences of the DNA that code for a protein that is not required.

You no longer know how splicing works? No problem, you can find an article about processing and splicing here.

At the level of translation, genes can be re-regulated. For example, more or fewer strands of mRNA can be formed, affecting protein biosynthesis. Because the more mRNA strands are present and the longer their lifespan, the more proteins can be produced, conversely.

In addition, proteins bound to the ribosomes can block the translation of a strand of mRNA, thus preventing the synthesis of the amino acid sequence. In this case, the initiation site of the ribosomal subunit is blocked.

Even after protein biosynthesis, gene regulation can still take place by activating or deactivating enzyme proteins. For example, some enzymes need to be allosterically activated before they can do their job in the cell.

Would you like to learn more about enzymes? Then also have a look at the article on enzymes and enzyme activity!

Gene regulation – the most important thing

  • Gene regulation describes the control of the activity of enzymes and is also understood under the synonym gene expression.
  • Gene regulation occurs because not all enzymes are needed at all times.
  • Gene regulation in eukaryotes and prokaryotes differ. While in prokaryotes gene regulation can only take place before transcription, in eukaryotes gene regulation can take place during transcription, translation or even after the synthesis of a protein.
  • In prokaryotes, gene regulation takes place according to the operon model, with promoter, operator and structural genes being understood as “operons” and a repressor gene preceding the operon.
  • The transcription rate of an enzyme can be affected either by substrate induction/positive gene regulation or by end product repression/negative.