biology-class-12-unit-06-chapter-10-genetics-and-evolution-molecular-basis-of-inheritance-l-10-12-rmphnv-p7x8

### <Success style="font-size:25px"> Genetics And Evolution Molecular Basis Of Inheritance L-10 </Success>
### <primary style="font-size:24px"> Regulation of gene expression in bacteria </primary>
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- **Terminology...**

- **Regulator Gene:** A gene that regulates the expression of one or more structural genes
 - **Structural gene:** One that forms templates for messenger RNA and is thereby responsible for the amino acid sequence of specific polypeptides
 - **Constitutive Gene:** Genes that are required for the maintenance of basic cellular function, and are <ins>expressed</ins> in all cells of an organism under normal conditions

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<footer style = "font-size: 18px">Genetics and evolution $\rightarrow$ Regulation of Gene Expression $\rightarrow$ <span style = "color:blue"> Regulation of gene expression in bacteria </span> $\rightarrow$ Regulation of gene expression in bacteria $\rightarrow$ What is operon? </footer>

- **Continue...**

- **Operator:** An operator is a segment of <ins>DNA</ins> to which a <ins>transcription</ins> factor binds to regulate <ins>gene expression</ins> by repressing it.

- **Repressor:** A repressor is a <ins>DNA</ins> or <ins>RNA</ins>- binding protein that inhibits the <ins>expression</ins> of one or more genes by binding to the operator or associated <ins>silencers</ins>.

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<footer style = "font-size: 18px">Regulation of Gene Expression $\rightarrow$ Regulation of gene expression in bacteria $\rightarrow$ <span style = "color:blue"> Regulation of gene expression in bacteria </span> $\rightarrow$ What is operon? $\rightarrow$ Types of operon system in Bacteria </footer>

### <Success style="font-size:25px"> Genetics And Evolution Molecular Basis Of Inheritance L-10 </Success>
### <primary style="font-size:24px"> What is operon? </primary>
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- An **operon** is a functioning unit of genomic DNA containing a cluster of <ins>genes</ins> under the control of a single <ins>promoter</ins>

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- A group of bacterial structural genes that are transcribed together (along with their promoter and additional sequences that control transcription) is called an **operon**

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<footer style = "font-size: 18px">Regulation of gene expression in bacteria $\rightarrow$ Regulation of gene expression in bacteria $\rightarrow$ <span style = "color:blue"> What is operon? </span> $\rightarrow$ Types of operon system in Bacteria $\rightarrow$ Inducible operon system </footer>

### <Success style="font-size:25px"> Genetics And Evolution Molecular Basis Of Inheritance L-10 </Success>
### <primary style="font-size:24px"> Types of operon system in Bacteria </primary>
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- **1. Inducible Operon:** An inducible operon is an operon in which the presence of a key metabolic substance induces transcription of the structural genes

- **Example-** Lac Operon

- **2. Reprssible Operon:** A repressible operon is an operon which always transcribes structural genes unless a repressor is present

- **Example-** Trp Operon

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<footer style = "font-size: 18px">Regulation of gene expression in bacteria $\rightarrow$ What is operon? $\rightarrow$ <span style = "color:blue"> Types of operon system in Bacteria </span> $\rightarrow$ Inducible operon system $\rightarrow$ Inducible operon system </footer>

### <Success style="font-size:25px"> Genetics And Evolution Molecular Basis Of Inheritance L-10 </Success>
### <primary style="font-size:24px"> Inducible operon system </primary>
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- Lactose (a disaccharide) is one of the major carbohydrates found in milk

- To utilize lactose as an energy source, _E. coli_ must first break it into glucose and galactose, a reaction catalyzed by the enzyme-Beta galactosidase

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<footer style = "font-size: 18px">Types of operon system in Bacteria $\rightarrow$ Inducible operon system $\rightarrow$ <span style = "color:blue"> Inducible operon system </span> $\rightarrow$ Organization of Lac Genes $\rightarrow$ Organization of Lac Genes </footer>

### <Success style="font-size:25px"> Genetics And Evolution Molecular Basis Of Inheritance L-10 </Success>
### <primary style="font-size:24px"> Organization of Lac Genes </primary>
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- The enzymes -beta galactosidase, permease, and transacetylase are encoded by adjacent structural genes in the lac operon of _E. coli_

- Beta-Galactosidase is encoded by the lacZ gene

- permease by the lacy gene, and transacetylase by the lacx gene

- In the lac operon, the lac Z, lac Y, and lac a genes have a common promoter

- Upstream of the promoter is a regulator gene, lac I, which has its own promoter (P)

- The lacl gene is transcribed into a short mRNA that is translated into a repressor Protein

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<footer style = "font-size: 18px">Inducible operon system $\rightarrow$ Organization of Lac Genes $\rightarrow$ <span style = "color:blue"> Organization of Lac Genes </span> $\rightarrow$ Regulation of Lac operon $\rightarrow$ Regulation of Lac operon </footer>

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### <primary style="font-size:24px"> Regulation of Lac operon </primary>
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- In the absence of lactose
 - The repressor binds to the lac operator site
 - When the repressor is bound to the operator, the binding of RNA polymerase is blocked, and transcription is prevented  
 - Genes are Switched Off

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<footer style = "font-size: 18px">Organization of Lac Genes $\rightarrow$ Organization of Lac Genes $\rightarrow$ <span style = "color:blue"> Regulation of Lac operon </span> $\rightarrow$ Regulation of Lac operon $\rightarrow$ Another model of lac operon regulation </footer>

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### <primary style="font-size:24px"> Regulation of Lac operon </primary>
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- When lactose is present
- Some of lactose is converted into allolactose
 - Allolactose binds to the repressor  
 - Causes the repressor to be released from the DNA- The repressor is inactivated 
- Binding of RNA polymerase is no longer blocked
- Transcription of lacZ, lacy, and lac a takes place, and the lac enzymes are produced
- Genes are Switched ON

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<footer style = "font-size: 18px">Organization of Lac Genes $\rightarrow$ Regulation of Lac operon $\rightarrow$ <span style = "color:blue"> Regulation of Lac operon </span> $\rightarrow$ Another model of lac operon regulation $\rightarrow$ Role of cyclic AMP in Lac Operon </footer>

### <Success style="font-size:25px"> Genetics And Evolution Molecular Basis Of Inheritance L-10 </Success>
### <primary style="font-size:24px"> Another model of lac operon regulation </primary>
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- Role of cyclic AMP (cAMP)

- CAP (inactive) combines with cAMP

- CAP-cAMP complex (Active) binds at CAP site of lac operon

- Complex recruit RNA polymerase to bind over the promoter to transcribe the lac gene

- Transcription followed by translation

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<footer style = "font-size: 18px">Regulation of Lac operon $\rightarrow$ Regulation of Lac operon $\rightarrow$ <span style = "color:blue"> Another model of lac operon regulation </span> $\rightarrow$ Role of cyclic AMP in Lac Operon $\rightarrow$ Organization of trp genes </footer>

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### <primary style="font-size:24px"> Role of cyclic AMP in Lac Operon </primary>
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- **Repressible Operon**

- Operons is normally turned on and must be repressed

- The trp operon contains five structural genes (trpE, trpD, trpC, trpB, and trpA)

- These produce components of three enzymes (two of the enzymes consist of two polypeptide chains)

- Upstream of the structural genes is the trp promoter

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<footer style = "font-size: 18px">Regulation of Lac operon $\rightarrow$ Another model of lac operon regulation $\rightarrow$ <span style = "color:blue"> Role of cyclic AMP in Lac Operon </span> $\rightarrow$ Organization of trp genes $\rightarrow$ In Absence of Tryptophan </footer>

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### <primary style="font-size:24px"> Organization of trp genes </primary>
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- **Trp E-** Anthranilate Synthetase (I)

- **Trp D-** Anthranilate Synthetase (II) (PRA Synthetase)

- **Trp C-** PRA-Isomerase InGP Synthetase

- **Trp B-** TryPetophen Synthetase B

- **Trp A-** Tryptophan Synthetase

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<footer style = "font-size: 18px">Another model of lac operon regulation $\rightarrow$ Role of cyclic AMP in Lac Operon $\rightarrow$ <span style = "color:blue"> Organization of trp genes </span> $\rightarrow$ In Absence of Tryptophan $\rightarrow$ In Absence of Tryptophan </footer>

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### <primary style="font-size:24px"> In Absence of Tryptophan </primary>
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- When tryptophan levels are low, RNA polymerase binds to the promoter

- Transcribes the five structural genes into a single mRNA

- mRNA translated into enzymes that convert chorismate into tryptophan

- Genes are Switched ON

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<footer style = "font-size: 18px">Role of cyclic AMP in Lac Operon $\rightarrow$ Organization of trp genes $\rightarrow$ <span style = "color:blue"> In Absence of Tryptophan </span> $\rightarrow$ In Absence of Tryptophan $\rightarrow$ In Presence of Tryptophan </footer>

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<footer style = "font-size: 18px">Organization of trp genes $\rightarrow$ In Absence of Tryptophan $\rightarrow$ <span style = "color:blue"> In Absence of Tryptophan </span> $\rightarrow$ In Presence of Tryptophan $\rightarrow$ In Presence of Tryptophan </footer>

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- Some distance from the trp operon is a regulator gene, trpR

- TrpR encodes a repressor that alone cannot bind DNA

- Binding with tryptophan causes a conformational change in the repressor that makes it capable of binding to DNA at the operator site, which overlaps the promoter.

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<footer style = "font-size: 18px">In Absence of Tryptophan $\rightarrow$ In Absence of Tryptophan $\rightarrow$ <span style = "color:blue"> In Presence of Tryptophan </span> $\rightarrow$ In Presence of Tryptophan $\rightarrow$ Trp operon also regulated by Attenuation </footer>

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<footer style = "font-size: 18px">In Absence of Tryptophan $\rightarrow$ In Presence of Tryptophan $\rightarrow$ <span style = "color:blue"> In Presence of Tryptophan </span> $\rightarrow$ Trp operon also regulated by Attenuation $\rightarrow$ Levels of Control of Gene Expression </footer>

### <Success style="font-size:25px"> Genetics And Evolution Molecular Basis Of Inheritance L-10 </Success>
### <primary style="font-size:24px"> Trp operon also regulated by Attenuation </primary>
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<footer style = "font-size: 18px">In Presence of Tryptophan $\rightarrow$ In Presence of Tryptophan $\rightarrow$ <span style = "color:blue"> Trp operon also regulated by Attenuation </span> $\rightarrow$ Levels of Control of Gene Expression $\rightarrow$ Levels of Control of Gene Expression </footer>

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### <primary style="font-size:24px"> Levels of Control of Gene Expression </primary>
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- mRNA Transcriptional Control  
 - Processing of pre mRNA Control  
 - Transport of mRNA to Cytoplasm Control  
 - Translational Control  
 - mRNA degradation Control  
 - Protein degradation Control

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<footer style = "font-size: 18px">In Presence of Tryptophan $\rightarrow$ Trp operon also regulated by Attenuation $\rightarrow$ <span style = "color:blue"> Levels of Control of Gene Expression </span> $\rightarrow$ Levels of Control of Gene Expression $\rightarrow$ mRNA Transcriptional Control </footer>

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- **Controlled by**

- Regulatory Proteins 
 - Promoter and enhancer 
 - General Transcription factors 
 - Activators
 - Repressors

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<footer style = "font-size: 18px">Levels of Control of Gene Expression $\rightarrow$ Levels of Control of Gene Expression $\rightarrow$ <span style = "color:blue"> mRNA Transcriptional Control </span> $\rightarrow$ mRNA Transcriptional Control $\rightarrow$ mRNA degradation Control </footer>

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### <primary style="font-size:24px"> mRNA Transcriptional Control </primary>
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- **Role of Chromatin in Regulating Transcription**

- **Chromatin Remodeling**

- Involves enzymes that modify nucleosome by acetylation and deacetylation

- 1. Histone Acetyl transferase enzyme

- 2. ATP dependent nucleosome remodeling complex

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<footer style = "font-size: 18px">Levels of Control of Gene Expression $\rightarrow$ mRNA Transcriptional Control $\rightarrow$ <span style = "color:blue"> mRNA Transcriptional Control </span> $\rightarrow$ mRNA degradation Control $\rightarrow$ mRNA degradation Control </footer>

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- **Processing of pre mRNA control**

- Includes-

- Alternative polyadenylation site
- Alternative splicing site

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- **Translational Control**

- RNA Interference which includes-

- Micro RNA (mi RNA)  
- Short Interfering RNA (siRNA)

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<footer style = "font-size: 18px">mRNA Transcriptional Control $\rightarrow$ mRNA Transcriptional Control $\rightarrow$ <span style = "color:blue"> mRNA degradation Control </span> $\rightarrow$ mRNA degradation Control $\rightarrow$ Protein degradation Control </footer>