Topic 1: Transcription Regulation

What is transcriptional regulation

Control of which genes are expressed when and how much

What is the purpose of transcriptional regulation

Allows cells to respond to signals differentiate and conserve energy by only expressing needed genes

What is a promoter

A DNA region where RNA polymerase binds to begin transcription

What do activators do

Bind specific DNA sequences to recruit RNA polymerase and increase transcription

What do repressors do

Bind regulatory DNA to block RNA polymerase or block activator binding reducing transcription

Do activators and repressors affect transcription directly

Yes they control whether RNA polymerase can initiate transcription

How does an activator increase transcription

By binding DNA and helping RNA polymerase bind the promoter

How does a repressor decrease transcription

By blocking RNA polymerase binding or blocking its movement or blocking the activator

What is negative regulation

A repressor prevents transcription unless removed

What is positive regulation

An activator is needed for transcription to occur

What is combinatorial control

The use of multiple transcription factors together to precisely regulate gene expression

What is the benefit of combinatorial control

Produces highly specific expression patterns using limited regulators

What is a transcription factor

A protein that binds DNA to regulate the transcription of specific genes

What is the difference between general transcription factors and specific transcription factors

General factors are needed for all transcription specific factors regulate only certain genes

What is an enhancer

A DNA sequence that activators bind to increase transcription often far from the promoter

What is the lac operon

A bacterial gene system that controls lactose metabolism based on glucose and lactose availability

What turns the lac repressor off

Lactose binds and inactivates the repressor so transcription can occur

When does CAP activate transcription

When glucose is low cAMP binds CAP so CAP can bind DNA and increase transcription

When is the lac operon most strongly expressed

When lactose is present and glucose is low

Why is the lac operon off when lactose is absent

The active repressor binds the operator and blocks RNA polymerase

What is the trp operon

A bacterial operon that turns off when tryptophan levels are high

What is corepression in the trp operon

Tryptophan binds the repressor which then binds DNA to shut off transcription

When is the trp operon on

When tryptophan levels are low so cells must synthesize more

What is positive feedback in gene regulation

A transcription factor activates its own gene increasing its own production

What is the effect of positive feedback loops

They create stable sustained gene expression states

What is negative feedback in gene regulation

A gene product inhibits its own production

What is the effect of negative feedback loops

They stabilize expression and prevent excessive transcription

Why do cells use feedback loops

To create stable gene expression states or respond precisely to environmental changes

What is the major advantage of transcriptional regulation

It saves energy by preventing unnecessary protein production