Gene expression in eukaryotes; cell communication

Differential Gene Expression

The process by which cells with the same DNA express different genes, leading to different phenotypes.

What factors might affect gene expression?

Environmental signals, transcription factors, epigenetic modifications, and the presence of specific molecules like inducers or repressors.

Operon

A cluster of genes under the control of a single promoter, allowing coordinated regulation of gene expression in prokaryotes.

Repression

The process by which a repressor protein inhibits gene transcription by binding to the operator region of an operon.

Induction

The process by which an inducer molecule binds to a repressor, preventing it from inhibiting transcription, thus allowing gene expression.

How do transcription factors facilitate gene expression in eukaryotes?

By binding to specific DNA sequences near a gene and recruiting RNA polymerase II

General Transcription Factors

Proteins that are required for the transcription of all genes, helping RNA polymerase to bind to the promoter.

Specific Transcription Factors

Proteins that regulate the transcription of specific genes, often in response to signals or in specific tissues.

TATA Box

a DNA sequence essential to precisely mark the start site for transcription and to define its direction

Chromatin Remodeling

The process by which the structure of chromatin is altered to expose or hide specific DNA sequences, affecting gene accessibility.

DNA Methylation

The addition of methyl groups to DNA, often leading to gene silencing by preventing transcription factor binding.

RNA Interference

A natural biological process that uses small RNA molecules to regulate gene expression by silencing specific genes

Activators

Proteins that bind to enhancer regions of DNA to increase the likelihood of transcription by facilitating RNA polymerase binding.

Corepressor

A molecule that binds to a repressor, enhancing its ability to inhibit transcription.

What happens when glucose concentration falls?

the body releases adrenaline to try to raise it, leading to symptoms like shakiness, sweating, and a rapid heartbeat

IPTG

An inducer for the lac operon by binding to the lac repressor protein, causing it to release from the DNA

How do inducible and repressible systems compare?

An inducible system is normally off but can be turned on by the presence of a specific molecule, called an inducer (like the lac operon), while a repressible system is normally on but can be turned off by the presence of a specific molecule, called a co-repressor (like the trp operon)

What are the three basic parts of an operon?

The promoter, the operator, and the structural gene(s).

What is the role of the lac repressor?

To inhibit the expression of the lac operon in bacteria when lactose is not available

Transcription Factors

Proteins that bind to regulatory DNA sequences to control the rate of transcription of genetic information.

Helix-Turn-Helix Motif

A protein structure composed of two alpha helices linked by a short turn, commonly found in DNA-binding proteins like transcription factors

Coactivators

Proteins that increase gene transcription by binding to transcription factors and helping to form a functional transcription complex

Enhancers

DNA sequences that, when bound by activators, can significantly increase the transcription of associated genes.

Transcriptional Control

Regulatory proteins, such as activators and repressors, influence the binding of RNA polymerase to DNA, thereby controlling gene expression.

What happens when tryptophan is present?

It binds to the trp repressor, activating it to block transcription of the trp operon.

What is the role of ribosomes in gene expression?

Ribosomes are the cellular machinery that translate mRNA into proteins during the process of translation.

What is the purpose of post-transcriptional regulation?

To control gene expression after transcription, allowing for rapid changes in protein levels and function.

Why is gene expression regulated?

Gene expression is regulated to ensure that the right genes are expressed at the right times and in the right amounts, allowing for efficient cellular function and response to environmental changes. Regulating enzyme activity can provide immediate responses, while transcriptional control allows for long-term changes in gene expression.

How do regulatory proteins interact with DNA?

Regulatory proteins interact with DNA by binding to specific sequences, often through DNA-binding motifs such as helix-turn-helix, zinc finger, and leucine zipper. These motifs allow proteins to recognize and attach to particular DNA regions, influencing gene expression.

What are operons?

Operons are clusters of genes that are transcribed together under the control of a single promoter. They are regulated by various mechanisms, including the presence of specific metabolites, allowing for coordinated expression of related genes, which can be more efficient for the cell.

What is negative gene regulation?

Negative gene regulation involves mechanisms that inhibit gene expression, typically through the binding of a repressor protein to the operator region of an operon, preventing transcription. The outcome is reduced or silenced gene expression.

What is positive gene regulation?

Positive gene regulation involves mechanisms that enhance gene expression, often through the binding of an activator protein to the promoter region, facilitating transcription. The outcome is increased gene expression.

What is the difference between repression and induction?

Repression is the process by which gene expression is decreased or turned off, often through the action of repressor proteins. Induction is the process by which gene expression is increased or turned on, typically through the action of inducer molecules that activate transcription.

Why is gene expression regulated?

Gene expression is regulated to ensure that proteins are produced at the right time, in the right amounts, and in response to environmental changes, allowing for efficient use of resources and adaptation to varying conditions.

How do regulatory proteins interact with DNA?

Regulatory proteins bind to specific DNA sequences, often in the promoter region, using DNA-binding motifs such as helix-turn-helix, zinc finger, or leucine zipper to influence the transcription of nearby genes.

What are operons?

Operons are clusters of genes under the control of a single promoter, typically regulated together, allowing for coordinated expression of genes that encode proteins with related functions, which enhances efficiency in gene regulation.

What is negative gene regulation?

Negative gene regulation involves mechanisms that inhibit gene expression, such as the binding of a repressor protein to the operator region, preventing transcription. The outcome is decreased gene expression.

What is positive gene regulation?

Positive gene regulation involves mechanisms that enhance gene expression, such as the binding of an activator protein to the promoter region, facilitating transcription. The outcome is increased gene expression.

What is the difference between repression and induction?

Repression is the process by which a repressor protein inhibits gene expression, while induction is the process by which an inducer molecule activates gene expression, leading to the production of specific proteins.

Trp Operons

Allows bacteria to stop making essential molecules that are already present to save energy and materials

Lac Operons

breaks down lactase- repressor is normally present, but is turned off by an inducer such as lactose so that transcription can occur

What are the lac and trp operons?

The lac operon is involved in the metabolism of lactose and is regulated by the presence of lactose and glucose, while the trp operon is involved in tryptophan synthesis and is regulated by tryptophan levels. Both operons exemplify feedback regulation mechanisms.