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Genes are one of the most crucial components of the human body, they carry the genetic information in the organisms and pass them on from one generation to the next one. In humans, genetic information is carried in the form of chromosomes. Gene regulation is one of the processes involved in gene replication and expression. Gene regulation refers to switching the genes on and then off. This article comprises all the essential topics for Gene regulation and frequently asked questions.
| Table of Content |
Keyterms: Gene, Chromosome, Gene replication, DNA, Codon, Protein, Polypeptide, mRNA, Amino acid, RNA, tRNA, prokaryotes, virus, bacteria
Read More: Genetic Drift
What is a Gene?
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We know, DNA, the genetic material, encodes signals for protein synthesis in the body. The entire portion of the DNA does not encode for protein synthesis, only a specific part of the DNA performs this function, and that specific part is called the gene. The DNA carries all the information required to pass on from one generation to another. It carries all the information that makes up an organism.
Each gene carries a set of sequences, called codons. These codons combine together to form a signal which makes up a set of proteins.
The genes are transcribed to form mRNA, this mRNA then undergoes transcription and forms proteins. Proteins perform all the biological functions in the body. A protein is a polypeptide sequence, made up of a series of peptides. Amino acids are the building blocks of protein.
Read More: Chromosomes and genes
What is Gene Regulation?
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Gene regulation is also called gene expression and includes turning a biological process on or off depending on the signals received. This in turn regulated the increase in production of some enzyme products or decreases their synthesis. They affect the transcription process and in turn RNA expression. They are modern biological procedures in turn to affect protein production.
Gene expression is essential for organisms such as prokaryotes, viruses, bacteria, etc., since gene expression regulates the expression of several biological processes.
Multicellular organisms also possess gene regulation. In them, it drives biological processes as cellular differentiation and morphogenesis in the embryo. Morphogenesis and cellular differentiation lead to the creation of different types of cells that in turn possess different gene expression profiles from the same genetic sequence.
Gene Regulation
Terms commonly used in Gene Regulation
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Up-regulation is a process in gene expression that occurs within a cell when the cell is triggered by a signal which is originating either internally or externally to the cell. Up-regulation causes a rise in the expression of one or more genes, which leads to an increase in the proteins encoded by those genes.
Down-regulation is a process in gene expression that occurs within a cell when the cell is triggered by a signal which is originating either internally or externally to the cell. Down-regulation results in decreased expression of one or more genes and as a result, the proteins encoded by those genes are also decreased.
Inducer: It is also called a repressor, which is an activation of a sensor that results in the change of expression of a gene.
Negative feedback: In a negative feedback mechanism, the gene product when present in more than the required amount, downregulates its own production directly or indirectly, which results in the following functions:
- It ensures keeping the transcript levels constant.
- It delays protein synthesis since it delays the transcription and translation processes.
Positive feedback: Here, the gene product produced as a result of transcription and translation, upregulates its own production directly or indirectly, which can result in
- signal amplification
- rapid protein synthesis
- pattern generation
Inducible systems - An inducible system is non-functional unless there is an inducer present that allows for gene expression.
Repressible systems - Except when particular molecules called corepressors are present, a repressible system is always functioning. Corepressor suppresses gene expression. This molecule represses the gene expression.
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Examples of Gene Regulation
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There are several examples of gene regulation, a few of them are stated below:
Lac operon
Lac operon
The lac operon gene of E. coli encodes the synthesis of enzyme b-galactosidase which hydrolyses lactose into galactose and glucose.
The lac operon gene contains three fragments that encode a functional protein. Cistrons (DNA fragments) encode proteins that can operate on their own or as subunits of bigger enzymes or structural proteins. The genes and their functions are:
- Z gene encodes for b-galactosidase
- Y gene encodes a permease that facilitates the transport of lactose into the bacterium cell
- A gene encodes a thiogalactoside transacetylase
Regulation of the lac Operon
Promotor controls the expression of the lac operon and its activity is regulated by two different proteins. One protein blocks RNA polymerase from transcribing (negative control), while the other boosts RNA polymerase binding to the promoter (positive control) (positive control).
Negative Control of the lac Operon
Lac operon is negatively regulated by a protein. This protein is a tetramer having four identical subunits called lac repressors. The lac repressor is encoded by the lacI gene, which is located upstream to the lac operon.
The lac repressor inhibits lac operon production in the absence of lactose by binding to the lac gene at the operator site, which is downstream of the promoter and upstream of the transcriptional start site.
The operator is made up of a unique nucleotide sequence that the repressor recognizes and binds to extremely strongly, preventing transcription from starting.
The lac repressor has a high sensitivity for lactose. When a small amount of lactose is present the lac repressor will bind to it and result in dissociation from the DNA operator thus freeing the operon for gene expression. This process is called the expression.
Positive Control of the lac Operon
Lactose can cause the lac operon to express, however, the degree of expression is relatively low. Lactose has been actively degraded to glucose and galactose since then.
The strength of a promoter is determined by its ability to bind RNA polymerase and to form a complex. The promoter for the lac operon, lactose, is weak and consequently, the lac operon is poorly transcribed upon induction.
A protein termed the catabolite activator protein has a binding site upstream from the promoter (CAP). When the CAP protein attaches to DNA, it distorts it, allowing the RNA polymerase to bind more efficiently, resulting in improved lac operon transcription.
Because circulating cAMP levels are low in the presence of glucose, the commencement of transcription from the lac operon is slowed. The quantity of cAMP decreases as glucose levels rise, activating CAP, which binds to the CAP site and stimulates transcription. A positive regulator is a cAMP-CAP complex.
Other examples:
- Enzyme induction
- Induction of heat shock proteins in the fruit fly
- Arabinose operon
- Tryptophan operon
Read More: Chromosomal Theory of Inheritance
Things to Remember
- Gene regulation is also called gene expression and includes turning a biological process on or off depending on the signals received.
- Up-regulation causes a rise in the expression of one or more genes, which leads to an increase in the proteins encoded by those genes.
- Down-regulation results in decreased expression of one or more genes and as a result, the proteins encoded by those genes are also decreased.
- In the negative feedback mechanism, the gene product when present in more than the required amount, downregulates its own production directly or indirectly.
- In a positive feedback mechanism, the gene product produced as a result of transcription and translation upregulates its own production directly or indirectly
Also Read:
Sample Questions
Ques: What is gene expression? (2 marks)
Ans: Gene regulation is also called gene expression and includes turning a biological process on or off depending on the signals received. This in turn regulated the increase in production of some enzyme products or decreases their synthesis. They affect the transcription process and in turn RNA expression. They are modern biological procedures in turn to affect protein production.
Ques: What are Up-regulation and down-regulation in gene expression? (2 marks)
Ans: Up-regulation is a type of gene expression that happens within a cell when it is activated by a signal that comes from either inside or outside the cell. Down-regulation is a process in gene expression that occurs within a cell when the cell is triggered by a signal which is originating either internally or externally to the cell.
Ques: What is negative feedback? (2 marks)
Ans: In a negative feedback mechanism, the gene product when present in more than the required amount, downregulates its own production directly or indirectly, which results in the following functions:
- It ensures keeping the transcript levels constant.
- It delays protein synthesis since it delays the transcription and translation processes.
Ques: What is positive feedback? (2 marks)
Ans: In positive feedback, the gene product produced as a result of transcription and translation, upregulates its own production directly or indirectly, which can result in
- signal amplification
- rapid protein synthesis
- pattern generation
Ques: Briefly explain the regulation of lac operon? (2 marks)
Ans: Promotor controls the expression of the lac operon and its activity is regulated by two different proteins. One protein blocks RNA polymerase from transcribing (negative control), while the other boosts RNA polymerase binding to the promoter (positive control) (positive control).
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