Regulation of Gene Expression

The environment of the cell

What regulates gene expression in prokaryotes and Eukaryotes?

Operon Model

In bacteria, gene regulation is controlled by the?

The operator

What part of the DNA strand works as the switch in gene expression?

Within the promotor region

Where are the operators positioned?

The operator, the promotor, and the genes they control

What parts of the DNA are part of the operon?

A protein repressor

What is responsible for switching the operator off?

By binding to the operator and blocking the movement of RNA polymerase.

How does the repressor block transcription?

The presence of other molecules

What is the repressor dependent on?

The corepressor

What is the molecule that cooperates with a repressor protein to switch the operon off?

Enzymes that make tryptophan

What does the trp operon code for?

It binds to the trp repressor proteins and moves the repressor on to the DNA and turns the operon off.

What happens when tryptophan is present in the environment?

Repressible operon (one that is usually on and needs to be turned on) and inducible operon (one that is usually off and needs to be turned on)

What are the two types if operons?

The Lac operon

What is an example of an inducible operon?

The Trp operon

What is an example of a repressive operon?

enzymes that break down lactose

What does the Lac operon code for?

A molecule that inactivates the repressor

What is an inducer?

Allolactose

What is the inducer for the Lac operon?

Repressible enzymes

What kind of enzymes are made from the Trp operon?

Inducible enzymes

What kind of enzymes are made from the Lac operon?

Catabolic (breaking down)

Inducible enzymes usually function is what kind of pathway?

Anabolic (Building)

Repressible enzymes usually function is what kind of pathway?

Negative control

The Trp and Lac operons are both what kind of control?

When glucose of scarce

When does the CAP (Catabolite activator protein) bind to the cAMP(cyclic AMP)?

the promotor

Where does the CAP and cAMP bind to?

Accelerate transcription

What does the binding of the CAP and cAMP to the promotor do?

When glucose levels increase

When does the CAP and the cAMP release from the promotor?

regulation of gene expression

What is the reason for cell specialization in multicellular organisms?

differences between cell types

Differences in gene expression result in?

Transcription

When is a common control point for gene expression?

DNA and proteins that help organize that DNA

What is chromatin made from?

Block off certain genes from being expressed

Histones influence the structure of chromatin and ___________

The addition of acetyl groups that loosen the chromatin and promotes initiation

What is histone acetylation?

The addition of a methyl groups that condense chromatin and stop transcription

What is methylation?

Cytosine

Where do the methyl groups attach in methylation?

Not expressed

When genes are more heavily methylated the genes are usually __________

inherited

The methylated genes are usually ________

The inheritance of traits transmitted by mechanisms not directly involving the nucleotide sequence

What is epigenetic inheritance?

reversed

The epigenetic mutations can be ________

Enzymes that provide initial control of gene expression by making a region of DNA more or less able to bind to transcription machinery.

What are chromatin- modifying enzymes?

Segments of DNA that serve as binding sites for transcription factors.

What are control elements?

different gene expression in different cells

Control elements and transcriptions factors are crucial for ________

proteins that assist RNA polymerase position correctly on the DNA strand

What are transcription factors?

control elements and specific transcription factors

The level of transcription in eukaryotes is dependent on _________

Control elements that are positioned on the DNA close to the gene being transcribed

What are proximal control elements?

Control elements that are positioned on the DNA far away from the gene being transcribed

What are distal control elements?

a region of the DNA that controls the transcription initiation complex

What are enhancers?

Proteins that bind to the enhancer and activate RNA polymerase

What are activators?

The region that binds to the DNA/Enhancer and the region that activates the proteins on the promotor

What are the two regions of Activators?

The region that facilitates a sequence of protein to protein interactions that result in transcription

What are bound activators?

mediator proteins

Bound activators contact what to initiate transcription?

The presence of transcription factors, control elements, activators, and enhancers

What is the main difference between eukaryotic and prokaryotic transcription?

Different RNA segments are used in different combinations to produce different proteins.

What is alternative RNA splicing?

The segment in between the start codon and the 5' end

What is the untranslated region of mRNA?

proteins that bind of specific portions of mRNA and block translation

What are regulatory proteins?

Selective degradation

What regulates the length of time a protein functions in a cell?

Molecules of ubiquitin

What marks a protein for destruction?

regulate gene expression

What do noncoding RNAs do?

Small single stranded RNA molecules that can bind to complementary mRNA sequences and block translation?

What are MicroRNAs?

The inhibit gene expression by RNA interference (RNAi)

What are small interfering RNAs (siRNAs)?

DNA found near the centromere in chromosomes

What is centromeric DNA?

siRNAs

Centromeric DNA can be processed into _________

Piwi-associated (piRNA)

The heavily condensed DNA at the centromere is formed by _______

transposons

piRNAs block the expression of _______

They express different genes for an identical genome

Why do cells in a given multicellular organism differ?

mRNAs being made

Identifying which genes are being expressed can be determined by determining the _________