Eukaryotic Gene Expression

Flashcards about Eukaryotic Gene Expression

What is the basic structure of a nucleosome?

DNA double helix wrapped around a core of eight histone peptides.

What is the role of the H1 protein in chromatin structure?

It attaches to linker DNA and the nucleosome to help stabilize the 30-nm fiber.

What is heterochromatin?

Most condensed form of chromatin where genes are inaccessible and transcriptionally silent.

What is euchromatin?

Less-condensed chromatin where genes are accessible and transcriptionally active.

How does acetylation of lysines affect gene activity?

Reduces positive charges on histones, decreasing affinity between adjacent nucleosomes and DNA, increasing gene expression activity.

How does phosphorylation affect gene expression?

Increases gene expression activity.

How does methylation affect gene expression?

Leads to chromatin condensation and typically reduces gene expression activity.

What is the effect of DNA methylation on transcriptional activity?

DNA methylation (typically on Cytosine residues) is associated with reduced transcriptional activity. Removing methyl groups reactivates genes.

What is dosage compensation?

The process by which organisms express the same number of genes across sexes, which is important because there are very few genes on the Y chromosome.

What is X chromosome inactivation?

Early in development, one X chromosome in females is inactivated through hypermethylation of DNA, leading to complete heterochromatinization and the appearance of a Barr body.

What is a Barr body?

The inactive X chromosome in female mammalian cells, appearing as a condensed structure.

What is the significance of calico cats in the context of X chromosome inactivation?

Coat-color genes on the X chromosome are randomly inactivated, resulting in the calico pattern, and calico cats are almost always female.

What is the initial level of control in the regulation of transcription?

Chromatin structure.

What is the role of transcription factors?

Transcription factors bind to DNA or to other proteins to facilitate or inhibit the binding of RNA polymerase to the promoter.

What is the function of enhancers?

Enhancers are distal gene control elements that can be thousands of bases away from the promoter and can function in either orientation to control transcription in different tissues or at different times.

How do enhancers stimulate transcription?

Enhancers stimulate transcription by binding activators and mediator proteins, which then interact with the basal transcription apparatus at the promoter.

What is combinatorial control of gene activity?

The precise control of gene activity depends on the combination of different transcription factors binding to control elements in enhancers.

How do eukaryotes control coordinately controlled genes?

Coordinated expression depends on the activation of a specific combination of control elements, often in response to a chemical signal like a hormone.

What is the true measure of gene expression?

The amount of functional protein in the cell.

What is alternative mRNA splicing?

A process where different mRNA molecules are produced from the same primary transcript, resulting in different proteins.

How does alternative RNA processing contribute to organism complexity?

Allows complex organisms to be generated with relatively few genes by producing multiple proteins from a single gene.

Why is mRNA stability important?

RNA stability determines the amount of protein produced.

How does the length of the poly-A tail affect mRNA stability?

The length of the 3' poly-A tail is a factor controlling mRNA stability; a longer tail generally leads to greater stability.

How is translation initiation controlled in eukaryotes?

Initiation can be blocked by proteins preventing mRNA and ribosomal subunit binding, lack of a 3' poly-A tail, or global arrest by modifying translation factors.

How can small RNAs affect translation?

Small RNAs like microRNA and silencer RNA can bind to mRNA and silence translation.

How is ferritin production regulated by iron levels?

When iron levels are low, a translational repressor binds to ferritin mRNA, preventing translation. When iron is present, it binds to the repressor, allowing translation to occur.

List some examples of posttranslational control.

Folding, phosphorylation, glycosylation, protein targeting, and proteolytic cleavage.

What is proteolytic cleavage?

The process by which a protein is cleaved to produce multiple hormones or functional peptides.

How are proteins marked for destruction?

Tagged with Ubiquitin.

Where does protein degradation take place?

Proteasome.