20 Questions
What is the main focus of the study conducted by Jacob and Monod in the 1950s?
Regulation of gene expression in E. coli
Which enzyme catalyzes the cleavage of lactose into glucose and galactose?
β-galactosidase
When are the enzymes involved in lactose metabolism expressed?
Only when lactose is available in the medium
What type of mutants were identified by Jacob and Monod that express all three genes in the absence of lactose?
Constitutive mutants
What did Jacob and Monod identify in E. coli mutants that were defective in the regulation of genes involved in lactose metabolism?
Mutants unable to express these genes even in the presence of lactose
Which type of regulatory sequences can stimulate transcription from a distance?
Enhancers
What is the example of an enhancer that requires upstream repeats for efficient transcription?
SV 40 enhancer
Which regulatory sequence is an example of enhancer that determines tissue-specific expression of genes?
Immunoglobulin enhancer
What type of proteins control transcription by binding to regulatory sequences and regulating RNA Polymerase II activity?
Transcription activators
Determination of eukaryotic regulatory sequences is done by ligating them to a reporter gene and introducing the plasmid into which cells?
Animal cells
Which gene encodes a protein that regulates transcription in the Lac Operon?
The 'i' gene
What happens when lactose is absent in the Lac Operon?
The repressor binds to the operator and prevents the binding of RNA polymerase to the promoter
How is positive control of transcription in E. coli exemplified by the effect of glucose on the lac operon?
Glucose represses the lac operon in the presence of lactose through a positive control system based on the cAMP levels
In eukaryotic cells, what primarily controls transcription at the level of initiation and during elongation?
Specific proteins called transcription factors
What is responsible for the synthesis of different types of RNAs in eukaryotes?
Eukaryotic RNA polymerase III
Which proteins bind to CAAT and GGGCGG [GC Box] sequences to stimulate transcription?
Transcription activators
What is the function of SP-1 factor in gene transcription?
It stimulates transcription by binding to the GC box
What is the role of histone acetylation in gene transcription?
It facilitates the binding of transcription factors to nucleosomal DNA
Which proteins compete with activators to connect to the regulator sequence?
Transcriptional repressors
In eukaryotes, which structures bind to the Regulator sequences, suppressing transcription?
Transcriptional repressors
Study Notes
- The Lac Operon in E. coli consists of genes encoding beta-Galactosidase, permease, transacetylase, and regulatory proteins.
- Transcription of the operon is controlled by the operator (o) which is adjacent to the transcription initiation site.
- Regulatory mutations are located in two distinct loci, 'o' and 'i'.
- 'o' gene mutants result in constitutive expression, while 'i' gene mutants cannot produce a functional product.
- The 'i' gene encodes a protein which regulates transcription by binding to the operator and preventing transcription.
- In the absence of lactose, the repressor binds to the operator 'o' and prevents the binding of RNA polymerase to the promoter, thus blocking the transcription of the three genes.
- Lactose binds to the repressor and prevents its binding to the operator region of DNA, allowing transcription.
- Control of transcription is mediated by the interaction of regulatory proteins with specific DNA sequences.
- The Lac operon studies revealed that there are regulatory sequences, such as the operator, called cis-acting control elements, and proteins, such as the repressors, called trans-acting elements.
- Positive control of transcription in E. coli is exemplified by the effect of glucose on the expression of genes involved in the breakdown of other sugars, such as lactose.
- Glucose represses the lac operon in the presence of lactose through a positive control system based on the cAMP levels.
- The cAMP + CAP complex binds to the target DNA sequences in the Lac operon and facilitates the binding of polymerase to the promoter, activating transcription.
- In eukaryotic cells, transcription is controlled primarily at the level of initiation and during elongation.
- Transcription is controlled by proteins that bind to specific regulatory sequences and regulate the activity of RNA polymerase.
- Chromatin modifications play key roles in the control of transcription in eukaryotes due to the packaging of DNA.
- Eukaryotic RNA polymerases require specific proteins called transcription factors to initiate transcription.
- Eukaryotic RNA polymerases are different from the single RNA polymerase in bacteria, with three different types in eukaryotes.
- The promoter region in eukaryotes consists of a TATA sequence, binding sites for transcription factors, and other regulatory sequences.
- Eukaryotic RNA polymerases require specific proteins called transcription factors to initiate transcription.
- Eukaryotic RNA polymerases I, II, and III are responsible for the synthesis of different types of RNAs.
Test your knowledge of the regulation of transcription in bacteria and eukaryotic cells with this quiz. Explore the role of cis-acting regulatory sequences, promoters, and enhancers in controlling gene expression.
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