Prokaryotic Gene Regulation Study Guide

Introduction:

• Gene expression in organisms is the process by which information in the DNA is finally converted into a functional product!

• The activation of certain genes and their respective proteins are determined by a complex series of interactions between genes, RNA molecules, proteins (including transcription factors), and other components of the expression system.

• Some genes are expressed constantly because they create proteins involved in fundamental metabolic activities. In contrast, others are expressed as part of the cell differentiation process or due to cell differentiation.

Quite simply, the ability to turn certain genes on and off is known as gene regulation.

Gene Regulation Process in Prokaryotes

Operons:

• Many prokaryotic genes are arranged into blocks known as operons, which are linked together and translated into a single mRNA that encodes two or more proteins.

• Operons frequently code for proteins that have similar activities.

• Operons are regulated in three ways: repressors, inducers, and activators.

• Repressors and activators bind to a DNA site adjacent to the genes in question

• Repressors prevent transcription of a gene, and activators increase the transcription of a gene in response to an external stimulus

• Inducers either repress or activate transcription based on the cell’s needs

Regulating an operon’s activity (rather than numerous single genes producing single proteins) allows for better coordination of the synthesis of several proteins simultaneously. The controlled lac operon in E. col, for example, encodes three enzymes involved in lactose metabolism.

Repression or induction can be used to control the expression of an operon (or even a single gene).

• When a tiny metabolite attaches to a repressor or inducer protein in a cell, the protein experiences an allosteric shift, allowing it to either bind or unbind to a regulatory DNA sequence based on whether it is being repressed or induced.

• In the lac and trp operons, this type of control can be noticed:

1. Gene repression and induction are both examples of gene regulation in the Lac operon.
2. Gene repression controls the Trp (tryptophan) operon.
3. Adjustments in intracellular metabolite levels reflect the metabolic condition of the cell in both operons and trigger corresponding changes in gene transcription.

Inducible and Repressible Operons:

• Some operons are normally “off,” but a small molecule can turn them “on.” This molecule is referred to as an inducer, and the operon is considered inducible. Lac operon is an example of this.

• Other operons are generally “on,” but a tiny chemical can switch them “off.” The molecule is referred to as a corepressor, and the operon is repressible. Tryptophan operon is an example of this.

Lac operon:

• The lac operon in E. coli regulates the utilization of lactose as a food substitute for glucose.
• LacZ, lacY, and lacA, also known as structural genes, make up the operon.
• Structural genes, by definition, code for proteins that are involved in cell structure and metabolism.
• The lac operon is translated into an mRNA that encodes the Z, Y, and A proteins.

Lactose (a disaccharide) is broken down into galactose and glucose by the enzyme galactosidase, encoded by the lacZ gene.

Lactose permease, a membrane protein that aids lactose entrance into cells, is encoded by the lacY gene.

The lacA gene (a transacetylase) has a mysterious role in lactose energy metabolism.

A regulatory gene is the I gene to the left of the lac Z gene (distinguish it from structural genes).

Source

Controlling the Transcription Process

1. To control transcription, regulatory genes encode proteins that interact with regulatory DNA sequences linked with a gene.

2. The transcription regulatory DNA sequence that separates the I and Z genes is called the operator sequence. Because E. coli organisms prefer glucose as an energy and carbon source, the lac operon is normally silenced (repressed).

3. When there is enough glucose, a repressor protein (the I gene product) binds to the operator and prevents the lac operon from being transcribed.

4. Even if lactose is present, cells will not utilize it as an energy source or carbon when glucose levels are sufficient.

5. On the other hand, the lac operon becomes active when glucose levels fall, and the three enzyme products are translated.

6. In E. coli cells, the repressor protein product of the I gene is always produced and present.

7. The repressor protein binds strongly to the operator DNA in the absence of lactose in the growing media.

8. The presence of the repressor tied to the operator sequence adjacent to the Z gene physically stops the forward movement of RNA polymerase. At the same time, it is attached to the promoter and ready to transcribe the operon. Little or no transcript is created under these circumstances.

9. Lactose entering the cells is transformed to allolactose when they are developed in the presence of lactose.

Conclusion:

• The biological mechanisms that govern the pace and method of gene expression are referred to as gene regulation.
• Many prokaryotic genes are arranged into operons, which are linked together and translated into a single mRNA that encodes two or more proteins.
• Some operons are normally “off,” but a small molecule can turn them “on.” The chemical is referred to as an inducer, and the operon is inducible. Lac operon in prokaryotes is an example of this.
• Other operons are generally “on,” but a tiny chemical can switch them “off.” The molecule is referred to as a corepressor, and the operon is repressible. Tryptophan operon is an example of this.
• The lac operon in E. coli regulates the utilization of lactose as a food substitute for glucose.

FAQs:

1. How do prokaryotes regulate genes?

Only the amount of transcription can be controlled by prokaryotic organisms to regulate gene expression. Controlling gene expression became feasible due to regulating transcription in the nucleus, RNA levels, and protein translation outside the nucleus.

2. What is the regulation of the prokaryotic genome called?

Regulation of the prokaryotic genome is mainly regulated through the operon systems.

3. Which explains the difference between prokaryotic and eukaryotic gene regulation?

Gene expression is largely controlled at the transcriptional level in bacterial cells. Eukaryotic gene expression is controlled in two ways: in the nucleus during transcription and RNA processing and in the cytoplasm during protein translation.

4. what is an example of prokaryotic gene regulation?

Lac operon is the most common example of prokaryotic gene regulation.

5. How do operons regulate gene expression in prokaryotes?

In prokaryotic cells, gene expression is controlled at the transcriptional level. Inducer molecules can activate activator proteins or inactivate repressors to enhance transcription.

6. What is the main difference between prokaryotic and eukaryotic gene regulation?

Gene expression is regulated by various factors (epigenetic, transcriptional, post-transcriptional, translational, and post-translational) in eukaryotes; however, gene expression can only be regulated in prokaryotes at the transcription level.

7. How is gene regulation in prokaryotes and eukaryotes similar?

Prokaryotes and eukaryotes both use proteins that serve as activators or repressors to control transcription. In prokaryotes, repressors are more frequent than in eukaryotes.

8. What is gene regulation in eukaryotes?

Gene expression in eukaryotes like humans includes multiple processes, and gene regulation can happen at any of them. Many genes, on the other hand, are largely controlled at the transcriptional level. Some of the levels where this can happen are epigenetic, transcriptional, post-transcriptional, translational, and post-translational.

9. How is translation different in prokaryotes and eukaryotes?

The primary distinction between eukaryotic and prokaryotic translation is that eukaryotic translation and transcription occur asynchronously(not simultaneously), whereas bacterial translation and transcription occur simultaneously.

We hope you enjoyed studying this lesson and learned something cool about Prokaryotic Gene Regulation! Join our Discord community to get any questions you may have answered and to engage with other students just like you! Don’t forget to download our App and check out our awesome VR classrooms- we promise, it makes studying much more fun! 😎

Sources:

1. Prokaryotic Gene Regulation. https://flexbooks.ck12.org/cbook/ck-12-biology-flexbook-2.0/section/4.12/primary/lesson/prokaryotic-gene-regulation-bio/. Accessed on 1 Dec, 2021.
2. 80 Prokaryotic Gene Regulation. https://opentextbc.ca/biology2eopenstax/chapter/prokaryotic-gene-regulation/. Accessed on 1 Dec, 2021.
3. Operons and Prokaryotic Gene Regulation. https://www.nature.com/scitable/topicpage/operons-and-prokaryotic-gene-regulation-992/. Accessed on 1 Dec, 2021.

]]>