Gene Expression and Operon Regulation

Inactivation of RNA by using another RNA is called RNA interference(RNAi). It is used in pest control in tomato plant. It is a cellular defence method. It is applicable to eukaryotes only.

So,
the correct option is ‘Eukaryotes’.

Lac-operon refers to the group of genes present in bacteria that are responsible for the metabolism of lactose. There are three genes called LacZ, LacY and LacA that code of beta-galactosidase, permease and transacetylase respectively. They have a common promoter, operator and a regulator gene.

A DNA segment that contributes to phenotype/function is called gene. In prokaryotes, the predominant site for control of gene expression is at Transcription level, where as in eukaryotes, control of gene expression occurs at transcription level, processing level, transport of mRNA, translation level.

So,
the correct option is ‘Transcription intiations’.

In E.coli, a single circular, nacked dsDNA molecule act as a genetic material. It contains 64 genes and are grouped into 20 operons.

So, the correct option is ’64, 20’.

In eukaryotes, the translation process begins at the start codon AUG, which codes for the amino acid methionine.

Operon can be defined as DNA segment having a cluster of genes which are controlled by single promoter. It consists of operator gene and structural genes. The operator gene regulates the expression of structural genes by providing a binding site to transcription factor which in turn regulate the gene expression by altering the binding of RNA polymerase to the promoter region. A promoter is a DNA segment where transcription of a particular gene starts. The regulator genes code for transcription factor/repressor proteins that binds to operators or promoters and prevent RNA polymerase from transcribing RNA. The alteration in repressor proteins by inducers make them unable to bind DNA and allow RNA polymerase to carry out transcription. Thus regulator gene control the functioning of structural genes via operator gene. Option C is correct answer.

Promoter is a DNA segment that serves to initiate transcription of a particular gene. They are present upstream near the transcription start sites of genes. Regulator gene regulates the expression of structural genes by its protein product that are mostly transcription factors. These transcription factors bind to the operator region which is located just upstream the binding site of the RNA polymerase and hence, prevent the binding and transcription. Operator is a DNA sequence present between the promoter region and the first coding gene. This operator region serves as repressor protein binding site. The gene that codes for any RNA / protein product which do not serve as regulatory protein are known as structural genes. The lac Z lac Y and lac A genes in lac operon are the structural genes. Option B is the correct answer.

Operon can be defined as DNA segment having a cluster of genes which are controlled by single promoter. It consists of operator gene and structural genes. The operator gene regulates the expression of structural genes by providing a binding site to transcription factor which in turn regulate the gene expression by altering the binding of RNA polymerase to the promoter region. A promoter is a DNA segment where transcription of a particular gene starts. Ligase enzymes facilitate the joining of two DNA strand together by phosphodiester bonds. The regulator genes code for transcription factor/repressor proteins that binds to operators or promoters and prevent RNA polymerase from transcribing RNA. The alteration in repressor proteins by inducers make them unable to bind DNA and allow RNA polymerase to carry out transcription. Thus regulator gene control the functioning of structural genes via operator gene. Option D is correct answer.

• Growth hormone helps in amino acid uptake in all the tissues and also help in the transcription process in which DNA is converted into mRNA.
  
• GH also help in synthesis of protein hormone.
• It also helps to decrease protein catabolism.

• Operator gene is a segment of DNA present between the promoter and the genes of the operon. It helps in transcribing the genes of the operon.
  
• Regulator gene often codes for repressor proteins which bind with the operator and checks the operon.
  
• Repressor gene physically obstructs the RNA polymerase from transcribing the genes by binding with the operator gene.
  
• Structural genes are the genes that undergo translation to produce enzymes and are co-regulated by the operon.
  
• Promoter gene is a nucleotide sequence that enables a gene to be transcribed. It is recognized by RNA polymerase, which then initiates transcription.
  

Regulation of functioning of the expression of genes is known as the regulation of gene expression. It is basically of three types- inducible, constitutive and repressible.

The promoter is a DNA segment that serves to initiate transcription of a particular gene. They are present upstream near the transcription start sites of genes. Regulator gene regulates the expression of structural genes by its protein product that is mostly transcription factors, also termed as the repressor. The operator is a DNA sequence present between the promoter region and the first coding gene. This operator region serves as a repressor protein binding site. The repressor binds to operator region which is located just upstream the binding site of the RNA polymerase and hence, prevent the binding and transcription; this makes option C incorrect. Regulator gene serves to regulate the expression of structural genes via repressor; it does not provide the binding site for RNA polymerase; option A is wrong. The inducer is a molecule that binds to repressor to prevent its binding to operator region and thereby, facilitates gene expression; option B is incorrect.

Regulator gene regulates the expression of structural genes by its protein products that are mostly transcription factors. These transcription factors bind to the operator region which is located just upstream the binding site of the RNA polymerase and hence prevent the binding and transcription; option D is correct. Operator is a DNA sequence present between the promoter region and the first coding gene. This operator region serves as repressor protein binding site; option B is wrong. Genes which govern more or less same trait or perform same role are called redundant genes; presence of these genes confers advantage of diluting the effect of point mutation on organisms; option C is wrong. Presence of more than one allele on a genetic locus is called gene polymorphism provided that the allele is present with more than 5% frequency in the population; option A is wrong. 

In genetics, a promoter is a region of DNA that initiates transcription of a particular gene. Promoters are located near the transcription start sites of genes, on the same strand and upstream on the DNA (towards the 5' region of the sense strand).

An operon is a functioning unit of genomic DNA containing a cluster of genes under the control of a single promoter. The genes are transcribed together into an mRNA strand and either translated together in the cytoplasm, or undergo trans-splicing to create monocistronic mRNAs that are translated separately. Regulator gene regulates inhibiting transcription of mRNA.

An operon is a cluster of genes under the control of a single promoter, functioning as a regulated unit of genetic material in prokaryotes.

The tryptophan operon is a repressible operon, meaning it is normally active and is turned off when the end product (tryptophan) is present in sufficient quantities.

The gene that codes for any RNA/protein product which does not serve as regulatory protein is known as structural genes. The operator is a DNA sequence present between the promoter region and the first coding gene. The operator region serves as the repressor protein binding site. The promoter is a DNA segment that serves to initiate transcription of a particular gene. They are present upstream near the transcription start sites of genes in between the operator and structural gene. The regulatory gene regulates the expression of structural genes by its protein products that are mostly transcription factors. It is not the part of an operon, which means that it is present upstream or downstream the structural genes but not in between; the Regulatory gene is present upstream the operator gene. Thus, the correct answer option D.

The regulator gene (or regulatory gene) is the part of the operon system that codes for the repressor protein.

In the operon model, the operator is the gene segment to which a repressor binds. This prevents the RNA polymerase from transcribing certain genes in the operon unit.

Lac repressor is part of the regulatory network of the lac operon. Lac repressor controls the production of three proteins produced from the gene and affecting the metabolism of lactose. This repressor molecule is a tetramer whose all the subunits are identical. This tetramer binds to a particular region in the bacterial DNA called the operator. This region is present next the three lactose metabolizing proteins. Binding of the repressor to operator causes the block in the production of protein. Otherwise, for three genes to transcribe the repressor protein binds to the lactose molecule and hence unable to bind to operator allows the genes to transcribe.

When E. coli is moved from glucose to a lactose-containing medium, the lac operon is induced to produce enzymes necessary for lactose metabolism.

In a repressible operon, the corepressor binds to the inactive aporepressor to form an active repressor complex that can bind to the operator.

In the lac operon, the active repressor protein binds to the operator site, physically blocking RNA polymerase from transcribing the structural genes.

An operon system typically includes the regulator gene, promoter, operator, and the structural genes it controls.

Telomeres, the ends of eukaryotic chromosomes, consist of repetitive DNA sequences that are typically rich in guanine.

The lac operon is a classic example of an inducible operon, meaning it is typically turned off but can be activated (induced) by the presence of lactose. Repressible operons, by contrast, are typically on and turned off by the presence of a product.

Eukaryotic genes are characterized by split gene organization, meaning they contain non-coding intervening sequences called introns that are removed during RNA processing. Prokaryotic genomes generally lack these introns.

An operon is a functional unit of DNA in prokaryotes consisting of a cluster of genes under the control of a single promoter and operator, allowing for the coordinated regulation of a metabolic pathway.

In eukaryotic cells, the DNA is contained within the nucleus, which is where the process of transcription (DNA to RNA) occurs. Translation then takes place in the cytoplasm.

Inducible operons are typically in an 'off' state due to the presence of a repressor protein bound to the operator. They are turned 'on' only when an inducer molecule binds to the repressor, preventing it from binding to the DNA.

During the processing of eukaryotic hnRNA, tailing (polyadenylation) involves the addition of a long chain of adenylate residues (poly-A tail) to the 3' end of the transcript to protect it and aid in export.

The regulator gene in an operon system codes for a repressor protein, which is responsible for binding to the operator site to inhibit transcription of the structural genes.

In prokaryotes, the peptidyl transferase activity, which catalyzes the formation of peptide bonds during translation, is an intrinsic function of the 23S rRNA component of the 50S ribosomal subunit.

DNA polymerase I is unique among the prokaryotic DNA polymerases because it possesses 5' to 3' exonuclease activity, which is essential for removing RNA primers during DNA replication.

DNA polymerase I is the only prokaryotic DNA polymerase that possesses both 3' to 5' exonuclease activity (for proofreading) and 5' to 3' exonuclease activity (for primer removal).

Prokaryotes lack split genes, meaning their coding sequences are continuous and do not contain introns. Eukaryotic genes are frequently interrupted by non-coding introns.

Split genes are genes that contain introns, which are transcribed into hnRNA (pre-mRNA) and subsequently removed during RNA splicing to produce mature mRNA.

In eukaryotes, RNA polymerase III is responsible for transcribing small RNAs, including tRNA and 5S rRNA. Therefore, its removal would specifically affect the transcription of tRNA.

In an operon system, a repressor protein binds specifically to the operator region of the operon, thereby physically preventing RNA polymerase from transcribing the structural genes.

Statements A, C, and D are generally considered correct in biological contexts. Statement B is incorrect because the lac operon is under positive regulation by CAP (Catabolite Activator Protein), not negative regulation. Thus, 3 statements are correct.

The regulator gene produces a repressor protein that binds to the operator, thereby inhibiting the transcription of the structural genes into mRNA.

In repressible systems, the inactive repressor (aporespressor) requires the corepressor to bind to the operator, meaning it can bind when the corepressor is present, not prevented by it. Thus, statement C is false and represents the wrong statement requested.

As the chimeric operon is under control of operator gene of lac operon, it will be functional only in the conditions required for lac operon to be functional. In lac operon lactose function as inducer hence its presence in medium is essential for proper functioning while glucose inhibits its function. So, the chimeric operon will produce tryptophan only when lactose is present and glucose is absent in the medium.

An operon, in genetics, is a functioning unit of DNA containing a cluster of genes under the control of a single promoter. The promoters are the palindromic sequences that control the process of transcription. An operon can be inducible like lac operon or it can be inhibitor operon like trp operon. 

The prokaryotic genetic system does not have a nucleus in their cell but the genome in a prokaryote is held within a DNA in the cytosol called nucleoid.

Regulation of gene expression refers to a very broad term that may occur at various levels. In eukaryotes the gene expression can be regulated at transcriptional level, processing level, transport of mRNA from nucleus to the cytoplasm, and translational level whereas in prokaryotes, control of the rate of transcriptional initiation is the predominant site for control of gene expression.

Operon model contains a cluster of genes which are under the control of single promoter. It consists of an operator, promoter, regulator and structural genes. The regulator gene function as a repressor as it produces repressor protein that binds to the operator and thus inhibits the transcription of the structural genes. It functions as regulator as it regulates the transcription of structural gene. The product of regulator gene is inhibitor that keeps the operon model turned off.

I. The z gene that codes for the enzyme beta-galactosidase that hydrolyzes lactose to glucose and galactose.

Morphogenesis is a process that controls the organized spatial distribution of cells during embryonic development. It can also take place in a matured organism in cell culture or in tumor cell masses. It is concerned with the shape of tissues. Plant growth regulators such as gibberellins, cytokinins, abscisic acid and ethylene control growth and development in plants. Gibberellins and cytokinins are the two instrumental hormones that play a key role in morphogenesis. Whereas auxins stimulate the plant cell to grow long.

In a repressible operon, the operon is normally on and transcription occurs for the synthesis of enzymes. This synthesis of enzymes takes place with the help of the structural genes.

The inducible operon is usually off and it can be induced in the presence of inducer like lactose. After getting induced, the operon is turned on and transcription takes place to catabolize these inducers. Hence, the inducible operon is usually involved in catabolism. 

Repressible operons are generally involved in anabolic pathways, or the synthesis of an essential component, while inducible operons are generally involved in catabolic pathways or the breakdown of a nutrient. Positive control of an operon is when gene expression is stimulated by the presence of a regulatory protein. The repressible operon work on the feedback inhibition mechanism which is the phenomenon where the output of a process is used as an input to control the behavior of the process itself and the co-repressor serves as to activate the repressor. Genes of a repressible operon are switched off as they are required to synthesize the structural/functional genes in the absence of the repressor. The presence of the repressor can stop this process and hence the repressor is present in the inactive form.