Lec-5 Transcription Regulation

What is the role of transcription regulators in gene expression?

Transcription regulators, including activators and repressors, control the expression of genes by binding to specific DNA sequences.

What is an operon, and where is it typically found?

An operon is a block of genes with related functions, transcribed together under the control of a single promoter, typically found in bacteria and archaea.

What are the three enzymes encoded by the lac operon?

The three enzymes are beta-galactosidase, permease, and transacetylase.

How does glucose affect the lac operon?

Glucose represses the lac operon, preventing its induction even in the presence of lactose.

What are enhancers in eukaryotic gene regulation?

Enhancers are DNA sequences that enhance the rate of transcription and can be located far from the promoter.

Describe how the lac operon is negatively regulated by lactose.

In the absence of lactose, the repressor binds to the operator, blocking transcription; when lactose is present, it binds to the repressor, allowing transcription to occur.

What role does adenylyl cyclase play in the regulation of the lac operon?

Adenylyl cyclase converts ATP to cyclic AMP; cAMP then binds to the CAP protein, facilitating RNA polymerase binding to the promoter.

What are core promoters, and what do they do?

Core promoters contain specific sequence elements that provide binding sites for general transcription factors and RNA polymerase, initiating transcription.

Define cis-regulatory elements in eukaryotic gene expression.

Cis-regulatory elements are DNA sequences that regulate the transcription of a gene located on the same chromosome.

How do chromatin-modifying proteins influence gene transcription?

They alter chromatin structure to make DNA more accessible, allowing transcription regulators and RNA polymerase to bind to the DNA.

What happens to transcription levels when enhancers are present?

The presence of enhancers significantly increases the transcription levels of associated genes.

What are the consequences of histone acetylation in transcriptional regulation?

Histone acetylation generally leads to a more loosely packed chromatin structure, promoting gene transcription.

Which transcription factor is responsible for recognizing the TATA box in eukaryotic transcription?

TFIID, specifically the TBP (TATA-binding protein) subunit.

What is the significance of RNA polymerase II in eukaryotic transcription?

RNA polymerase II is the enzyme responsible for synthesizing mRNA from DNA during transcription.

Explain the function of the i gene in the lac operon.

The i gene encodes a repressor protein that inhibits transcription of the lac operon in the absence of lactose.

How do eukaryotic transcription activators enhance transcription across large distances?

Eukaryotic activators can enhance transcription by looping DNA to bring their regulatory sequences into proximity with the promoter.

What are histone deacetylases (HDACs) and their role?

HDACs remove acetyl groups from histones, leading to chromatin condensation and reduced gene transcription.

How does the looping of DNA support enhancer action?

DNA looping allows enhancer-bound activators to interact with transcription machinery at the promoter, facilitating transcription initiation.

What is the general function of cohesin proteins in chromosomal organization?

Cohesin proteins stabilize chromosomal loops, helping maintain the spatial arrangement of genes and their regulatory elements.