Prokaryotic gene regulation

What determines the structural and functional differences in cell types despite all body cells having the same genes?

Patterns of gene expression result in different sets of proteins.

What is gene regulation?

The control of gene expression to ensure proteins are made at the right time, place and quantity.

Why is gene regulation essential for cells?

It is essential for cell function and response to environmental changes.

What are housekeeping genes?

Genes that are expressed in almost all cell types and keep basic cell functions operating normally.

What are regulated genes?

Genes that may or may not be expressed at any given time or in a given cell type, and their expression is controlled.

What is transcriptional regulation?

Transcriptional regulation involves processes that directly control gene expression, determining which genes are transcribed into mRNA.

What additional controls affect mRNA?

Additional controls that affect mRNA include its processing, translation into proteins, and the life span and activity of proteins (posttranslational regulation).

How do prokaryotic cells adapt to environmental changes?

Prokaryotic cells rapidly alter biochemical pathways by turning off genes for unnecessary metabolic processes and turning on genes for needed metabolic processes.

What is an example of gene regulation in E. coli?

When lactose is present, E. coli produces enzymes to digest it; when lactose is absent, it does not produce those enzymes.

What are the three levels at which gene regulation occurs?

Gene regulation can occur at transcriptional control (slow), (pre)translational control (moderate), and posttranslational control (fastest).

What is the order of control from DNA to protein?

The order of control is: DNA (1) > RNA (2) > Protein (3

What is an operon?

An operon is a cluster of prokaryotic genes and associated regulatory sequences.

What does an operon contain?

An operon contains several genes that are all transcribed into a single mRNA, directed by a promoter for RNA polymerase.

What is a transcription unit?

The cluster of genes transcribed into a single mRNA is called a transcription unit, typically encoding proteins involved in the same function.

What are regulatory sequences?

Regulatory sequences are DNA sequences where specific proteins can control the expression of a gene or genes.

What role do regulatory proteins play?

Regulatory proteins bind to regulatory sequences to control the transcription of genes.

What is a promoter?

A promoter is the site where RNA polymerase binds to begin transcription.

What is an operator?

An operator is a regulatory DNA sequence where regulatory proteins bind, affecting gene expression (stop/go).

What is a repressor protein?

A repressor protein negatively controls operons by preventing the operon genes from being expressed.

What is an activator protein?

An activator protein positively controls operons by turning on gene expression.

What structural genes are involved in the lac operon?

The lac operon includes three structural genes: lacZ, lacY, and lacA, which are transcribed in a single unit with a single promoter.

How is the lac operon regulated?

The lac operon is negatively regulated by the Lac repressor, a regulatory protein encoded by the lacI gene, which is separate from the lac operon.

What happens to the lac operon when lactose is absent?

When lactose is absent, the Lac repressor inhibits transcription by binding to the operator, blocking transcription of the structural genes.

What is the role of allolactose in the lac operon?

Allolactose, an isomer of lactose, serves as the inducer that inactivates the Lac repressor, allowing transcription of the operon structural genes.

What type of operon is the lac operon?

The lac operon is classified as an inducible operon.

How does the lac operon ensure transcription when lactose is the only energy source?

A positive gene regulation system ensures the lac operon is transcribed if lactose is the only energy source, but not if glucose is present alongside lactose.

What is the function of CAP in the lac operon?

CAP (catabolite activator protein) is an activator that stimulates gene expression by enabling RNA polymerase binding when glucose is absent.

What triggers CAP activation?

CAP is activated by cAMP and binds to the CAP site in the promoter when glucose is absent, facilitating transcription.

What is the function of the Lac repressor?

The Lac repressor inhibits transcription of the lac operon genes when lactose is absent by binding to the operator region.

What is prokaryotic gene regulation?

Prokaryotic gene regulation is the process by which bacteria control the expression of their genes in response to environmental changes or developmental stages.

What is an ORF?

An ORF, or open reading frame, is a continuous stretch of nucleotides that can be translated into a protein, starting with a start codon and ending with a stop codon.

What does UTR stand for, and what is its significance?

UTR stands for untranslated region, which refers to segments of mRNA that are not translated into protein but play crucial roles in regulating translation and stability.

What is transcription in the context of gene expression?

Transcription is the process of synthesizing RNA from a DNA template, converting genetic information from DNA to RNA.

What is translation in the context of gene expression?

Translation is the process of synthesizing proteins from an mRNA template, converting genetic information from RNA to proteins.

What is a transactional unit in gene regulation?

A transactional unit refers to a segment of DNA defined by its start and end points for transcription, encompassing the regions necessary for RNA polymerase to synthesize RNA.

What is an operon?

An operon is a cluster of genes under the control of a single promoter, functioning together to regulate gene expression in prokaryotes.

What is the lac operon and its role?

The lac operon is a negative control system regulating lactose metabolism in E. coli, enabling the breakdown of lactose when needed.

What are the components of the lac operon?

The lac operon contains a promoter (where RNA polymerase binds), an operator (where the repressor binds), and structural genes that code for enzymes needed for lactose metabolism (lacZ, lacY, lacA).

Under what conditions is lactose metabolism activated in E. coli?

Lactose metabolism is activated when high levels of lactose and low levels of glucose are present, leading to transcription of the lac operon.

What is the function of B-galactosidase in lactose metabolism?

B-galactosidase cleaves lactose into allolactose, glucose, and galactose, facilitating its metabolism in bacterial cells.

What happens when the Lac repressor is present?

When the Lac repressor is present, it binds to the operator and prevents transcription, effectively turning off lactose metabolism.

What is a regulatory protein?

A regulatory protein is one that binds to a regulatory sequence in DNA and affects the expression of associated genes.

What is negative control in gene regulation?

Negative control refers to gene expression being inhibited by a repressor protein, preventing transcription when the repressor is active.

How is gene expression turned on in negative control systems?

Gene expression is turned on in negative control systems by the absence or deactivation of the repressor, allowing transcription to proceed.

What is positive control in gene regulation?

Positive control enhances gene expression through the action of an activator protein, which turns on transcription when present.

How is gene expression turned off in positive control systems?

In positive control systems, gene expression is turned off in the absence or deactivation of the activator protein, preventing transcription.

What does the Lac I gene code for?

The Lac I gene codes for the lac repressor, which is synthesized in its active form and inhibits transcription when bound to the operator.

What is the function of the Lac Z gene?

The Lac Z gene codes for B-galactosidase, which cleaves and breaks down lactose into glucose and galactose.

What does the Lac Y gene code for?

The Lac Y gene codes for permease, which is a protein channel that transports lactose into the cell.

What is the function of the Lac A gene?

The Lac A gene codes for transacetylase, which exports excess sugar from the cell.

What happens when lactose is absent in the lac operon?

When lactose is absent, the lac repressor binds tightly to the operator, preventing RNA polymerase from working and inhibiting transcription.

What is an inducer in the context of the lac operon?

An inducer is a small molecule that triggers transcription by deactivating the repressor, allowing gene expression to occur.

What role does allolactose play in the lac operon?

Allolactose is the inducer of the lac operon; it binds to the lac repressor, deactivating it and allowing transcription to proceed.

What are the steps involved when lactose enters the cell?

Lactose enters the cell, B-galactosidase enzyme converts some lactose into allolactose, allolactose binds to the lac repressor, deactivating it, allowing transcription to occur.

What are the actions of the lac operon when induced?

When induced, permease molecules transport lactose into the cell, B-galactosidase converts lactose into allolactose, allolactose inactivates the lac repressor, RNA polymerase binds to the promoter, and transcription occurs.

What is the preferred energy source for E. coli?

Glucose is the more efficient (preferred) energy source than lactose for E. coli.

How do high glucose levels affect the transcription of the lac operon?

Transcription of the lac operon is inhibited when glucose levels are high, as E. coli prefers to use glucose over lactose.

What happens to the transcription of the lac operon when glucose levels are low?

Transcription of the lac operon is enhanced when glucose levels are low, as the cell turns on lactose metabolism in the absence of preferred energy sources.

What is CAP (Catabolite Activator Protein)?

CAP is a regulatory protein that is inactive without cAMP and plays a crucial role in the positive control of the lac operon.

What triggers the production of cAMP?

cAMP is produced when glucose levels are low, and it is synthesized by the enzyme adenylyl cyclase.

What happens when cAMP binds to CAP?

When cAMP binds to CAP, they form a complex that enhances the binding of RNA polymerase to the promoter, leading to better transcription of the lac operon.

Under what conditions is the lac operon transcription enhanced?

The lac operon transcription is enhanced when glucose levels are low and lactose is present, allowing allolactose to inactivate the repressor.

What effect does high glucose have on the lac operon transcription when lactose is present?

When glucose is high and lactose is present, the transcription of the lac operon is inhibited, as glucose inactivates adenylyl cyclase, resulting in low or no cAMP levels.

What is the result of low allolactose in the presence of high glucose?

With high glucose, lactose is converted to allolactose, but since allolactose levels are low, the repressor remains active, inhibiting transcription of the lac operon despite lactose presence.

How does glucose influence gene expression in the lac operon?

Glucose inactivates adenylyl cyclase, leading to low cAMP levels; without cAMP, the CAP cannot be activated, preventing gene expression even if lactose is available.

In the context of the lac operon, what type of control is exerted?

The lac operon is subject to some positive control through the activation of CAP by cAMP, which enhances transcription under specific conditions.

What is tryptophan?

Tryptophan is an amino acid necessary for protein synthesis.

What happens to the Trp operon when tryptophan is present?

The Trp operon is repressed when tryptophan is present, inhibiting the transcription of its genes.

What occurs with the Trp operon when tryptophan is absent?

The Trp operon is activated when tryptophan is absent, allowing transcription to proceed for tryptophan synthesis.

What is the structure of the Trp operon?

The Trp operon is a transcriptional unit made of five genes that code for tryptophan synthesis enzymes.

How is the Trp repressor activated?

The Trp repressor is activated when tryptophan binds to it through allosteric binding, leading to the repression of the operon.

What is a repressible operon?

A repressible operon is one where transcription is turned off by the activation of a repressor protein, preventing gene expression.

What is a corepressor in the context of the Trp operon?

A corepressor is a regulatory molecule, such as tryptophan, that activates the repressor to turn off gene expression in the Trp operon.

What is negative feedback inhibition?

Negative feedback inhibition is a regulatory mechanism where the product of a pathway inhibits its own production, such as tryptophan inhibiting its own synthesis pathway.