Gene expression, Introduction and mechanism

Gene expression, Introduction and mechanism

Introduction to Gene Expression

Chemically, a gene is a segment of DNA or a specific sequence of nucleotides. Alkali sequences vary in different genes. The functional gene is a segment of DNA that controls the synthesis of proteins.

Thus, we can say that the gene expresses itself as a protein enzyme, controlling specific traits or specific function enhancements.

Phenotypic expression of characteristics in the organism controls the alteration of genes. Phenotypic expression of characteristics in the organism is the result of a series of molecular biosynthetic activities regulated by genes in the cell.

Gene expression,Introduction and mechanism
Gene expression

Structural GeneGenes in which information about the sequence of amino acids of a polypeptide (protein) is coded. That is, which determines the composition of the protein. Genes coding for β – galactosidase, permutation, and transacetylase in lactose operon. They are linked.

House Keeping or Constitutive Gene)

The gene whose product the cell needs all the time, ie the gene that is a constant expression. Such as enzyme-related genes of the glycolysis pathway.

Operon – A group of structural genes in prokaryotes that are controlled together and transcribed as an m-RNA + the control element (promoter + operator) adjacent to them.

Promoter – Place of DNA where RNA Polymerase joins and starts transcription.

Inducer – Molecules capable of induction, such as allolactose.

Repressor Protein – a protein that prevents transcription by linking to the operator. That is, the molecule that is bound by the operator to the RNA. Pauses the path of polymerase and switches off.

Regulatory Gene – The gene that produces the repressor.

Co-Repressor – The molecule that binds the repressor to form the repressor + corepressor complex. It switches off by connecting to complex operators. Such as tryptophen.

Exons – The parts of the gene that contain information related to the structure of the protein and form part of the processed m-RNA.

Intron – regions of the gene that do not form part of m-RNA and are removed at the time of m-RNA processing are called introns.

Splicing – A method of m-RNA processing in which undesired RNA segments (coded by introns) are removed and regions coding for amino acids (coded by exons) are added.

Enhancers – Regulatory elements that can be located on either side (upstream or downstream) and far away from the coding region of the gene.

Feedback control – A mechanism in which the accumulation of the product of action affects the rate of its production.

Positive Control – mechanism in which activator protein (S) binds to speed up transcription.

Negative Control – Systems in which DN. a. The protein that binds to it is the repressor ie which switches off and transcribes.

Regulon – A group of an operon that is controlled by a single regulator.

Transcription Factors – Molecules such as lactose repressor, tryptophan repressor, and catabolite activator protein, which are used in DN. a. Affect transcription by connecting to.

Meaning of Gene Expression

The molecular-level mechanism of a gene expressing itself in a phenotype in an organism is called gene expression. It involves the synthesis of a variety of RNAs, polypeptides, enzymes, and structural proteins, which are essential for the control of specific activities and traits of the organism.

The synthesis of different types of tRNA from DNA is called transcription and the process of synthesis of a polypeptide chain from mRNA is called duplication. Genes are expressed by polypeptide chains, forming structural proteins, enzymes and other biochemicals containing proteins. Now, these substances provide biological responses to the living system.

Mechanism of Gene Expression

Gene expression is accomplished by a series of events. The information present in the DNA is converted into molecules that are determined by the cell’s anabolism.

During the gene expression process, the first copy of DNA occurs in the RNA molecule, which determines the amino acid sequence of the protein molecule. Synthesis of RNA molecules takes place using part of the alkali sequences of single-stranded double-stranded DNA.

Gene expression, mechanism
Gene expression

This single strand is called a mold. Therefore the formation of RNA transcription is facilitated by the RNA molecule polymerase enzyme, hence the process of synthesis of an RNA molecule from analogy genes is called transcription.

Proteins are synthesized in a definite sequence using alkali sequences and RNA molecules. Proteins are synthesized after the end of duplication. Therefore, gene expression refers to protein synthesis through two main events, namely transcription, and transcription.

Gene-expression is an action occurring at the molecular level in which the gene expresses itself as a phenotype of the organism. The mechanism of gene expression is based on biochemical genetics.

It contains polypeptide, enzyme, or a specific type of RNA. Synthesis, which controls the structure or function of a particular characteristic. Jean to M-R.N.A. (m-RNA) is called transcription.

In this process, the genetic information contained in the gene is transcribed as m-RNA. Some genes produce rRNA or t-RNA. DN in transcription a. Only one strand of a bifurcated molecule participates.

The mRNA enters the cytoplasm leaving the nucleus and translating the information of the gene as a sequence of amino acids in the polypeptide. T-RNAs play an important role in translation.

Gene-Expression in Prokaryotes

Regulation of gene expression in a prokaryotic cell, such as bacteria and blue-green algae, is often only for economical use of resources and for achieving energy efficiency.

As a result, the regulation of gene expression in prokaryotes is mostly at the transcription level. On the other hand, due to the greater need for regulation of development and development of eukaryotic cells and organisms, there is a great harmony between the various types of regulatory processes described above.

For this reason, eukaryotic gene expression is regulated at multiple levels.

DN in a bacterial cell. It is about one-thousandth of the volume. The only chromosome of a bacterial cell is also around DN. a. Consists of a molecule.

In prokaryotes, the genetic material is indistinguishable from the cytoplasm by Nuclear Membrane, as they lack cell art.

The multiplication (division) of bacteria occurs very rapidly. The time taken to form two cells by a division of one cell is called Generation Time. In some bacteria, this time is only 20 minutes. DN of bacteria a. Replication starts at only one location.

Reproduction (division) in bacteria is usually done by the asexual method ie, unlike eukaryotes, there is no exchange of Genetic Material in them. But some bacteria exhibit this exchange of genetic material.

You have read about the Transformation method. By this method, one strain of the pneumococcus bacterium Diplococcus pneumoniae is transformed into another.

DN of a distinction a. The second distinction present in the medium by DN a. It happens only after it has been accepted. External DN a. The phenotypic characters of the receptive bacteria are changed by the eclipse.


Performs plasmid replication with Fertility Factor. Its copy is transferred to the Recipient Cell by the conjugate tube. The receptor cell also becomes a donor. This phenomenon is called Sexduction.

(Gene-Expression in Viruses)

Viruses are Obligate Parasites, which consist of nuclear acids and proteins. Outside the cell, they remain inert. Inactive virus outside the cell is called Virion.

Tobacco Mosaic Virus was the earliest discovered virus. In 1880, Adolf Mayer stated that Tobacco Monkey’s disease is transmitted to healthy plants by the juice of the patient plant.

Iwanowsky is credited with the discovery of the virus. He told that even if the sap of the patient sap (sap) is filtered with a bacterial filter, the juice still can infect a healthy plant. Stanley first obtained the virus in crystal form.

Only one type of nuclear acid (ie DNA or RNA) is found in viruses. They lack cellular structure. Since viruses do not have their cellular machinery.

Therefore, they use the cellular machinery of the nutrient cell (eg ribosomes, enzymes, etc.) for expression of their genes and their reproduction. The action of the viral gene is also to make the host cell infected with the virus.

There are two types of action of viruses inside the cell:

  1. Lytic-Cycle
  2. Lysogenic-Cycle


The reproduction of a Virulent Phage is called Lytic-Cycle. This is called the lytic cycle due to the lysis of nutritious effort (bacteria).

Viruses that do not form prophage inside the nutrient cell are called virulent viruses. In this cycle, the virus first attaches to the bacterial cell.

In the next term, it inserts its nuclear acid into the bacterial cell. Upon reaching the cell, the virus gene takes over the cellular machinery of the bacterium and forms the viral protein, nuclear acid. After some time, the bacterial cell bursts and newly synthesized viruses come out. This is called lysis.

(Lysogenic Cycle)

Some viruses bind to the genetic material of the nutritive cell to form prophage, these are called temperate viruses and multiplications called lysogeny.

The λ phage attaches itself to the E. coli cell. Its DN in the next post. a. (DNA) is inserted into the bacterial cell. DN here a. There are two opportunities in front of me.

Like the T4 phase, it can multiply viruses by giving rise to the lytic cycle. Secondly, it is the DNA of the chromosome of bacteria. a. It can form prophage by connecting to.

In this cycle, the phase does not control the cellular machinery of nutrients. DN of Nutrition a. Replicate with. Repressor Protein, produced by prophase, does not allow other phage genes to be expressed, ie in a repressed state.

The prophage may be activated under changed environmental conditions. In such a state, the formation of the repressor protein is stopped by the prophase. As a result, genes related to Lytic-Cycle are activated. That is, the prophage now converts into a lytic phage and starts the lytic cycle.

Since the E. coli cell carrying the prophase is capable of displaying lysis, this type of cell is called a lysogenic cell. Phase DNA. DN of the bacterial cell a. It is known as Lysogeny in prophage.

Gene-Expression in Eukaryotes

Gene expression, Introduction and mechanism

 (Regulation of Gene Expression in Eukaryotes):

In eukaryotic, multicellular organisms, groups of cells cooperate for the division of labor.

Unlike prokaryotes, eukaryotes require some additional and specific methods of gene expression regulation, which provide a cell with the ability to perform a specific function and to group a group of cells into tissues (organs) and organs.

We know that Eukaryotes DN a. DNA replication, transcription, translation are more complex than prokaryotes. This complexity is also helpful in providing additional opportunities and methods for gene regulation in eukaryotes.

In simple words, we can also say that since the same gene in eukaryotic organisms may require different types of regulation in different cells. Thus gene regulation in eukaryotes is complex.

Eukaryotic cells often have longer life spans than prokaryotes, during which they may have to react to various types of stimuli several times. Instead of making new enzymes every time, these cells try to take action by altering some of the pre-made enzymes.

In gene regulation of multicellular eukaryotes, specificity is given to the specificity of the type and function of cells in each tissue. Each type of cell has a few active genes and some genes that are never used.

It is clear that the benefits of cellular support in multicellular organisms are more than the slight loss of carrying of inactive genes and certain chemicals by cells.

Unlike many prokaryotic genes, most eukaryotic genes are not found as operon-like clusters. Nevertheless, each eukaryotic gene has specific regulatory sequences that are necessary for the control of transcription.

The expression of Constitutive Genes of eukaryotic organisms occurs all the time. Inducible Genes are also found in these organisms to sensitize to environmental hazards such as overheating, heavy metal, and viral infections.

Growth and development in multicellular organisms are also complex. Some of the genes found in these are induced in the particular phase of the life of the organism. Their control is subject to the Temporal Regulation Mechanism.

Other genes are subject to Tissue-Specific Regulation. For example, a gene responsible for the formation of a particular enzyme, different from one type of tissue in a particular tissue, and another completely different type of tissue (Stimulus) in another type of tissue and regular different type of stimulation (Stimulus) in third tissue. (Regulated).

Mechanism and Expression of Genes

According to studies of various mutations – the form of the action of a gene is chemical. Genes perform important functions in supporting the formation of enzymes and controlling cellular metabolic processes.

Genes transmit the Genetic Code of Protein Synthesis on ribosomes via mRNA. Each gene shows a specific genetic effect.

Its specificity depends on the fraction of its DNA. In each gene, two thousand or more functional points are arranged in a sequence. Each of their units consists of groups of hundreds of thousands of nucleotides and the nucleotides are also arranged in a particular order.

The sequence of the four types of nucleotides determines gene specificity. Some genes show permanent direct effects, while some have direct effects that change by external or internal environments, or both. Genes are affected by factors like temperature, sunlight, hormones, etc.

Despite the lack of growth hormones, the living dwarf remains despite the genes of elongation. Similarly, sex hormones also sometimes affect the direct effects of genes.

The addition of a gene that is located on one chromosome can affect other chromosomes. Such genes are called modified genes. The expression of the direct effect of a gene is variable in time.

Many genes show their effect only at the time of the organism’s origin and some genes show their effect only a few weeks, months or years after birth, such as the time of scalp hair does not normally occur in humans before 25-30 years of age. 

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Gene expression, Introduction and mechanism

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