Regulation of gene expression 1

Question 1

Structural genes for proteins with related function are grouped together. These units are known as:

Answer 1

Operons

Question 2

Pevents binding of RNA polymerase to promoter

Answer 2

Repressor

Question 3

Tryptophan functions as a corepressor meaning

Answer 3

As the level of Trp increases within the cell this will inhibit the transcritption of the Trp operon

Question 4

Benefits of regulating gene expression

Answer 4

Versitility and adaptation

Conservation of energy

Necessaary during development

Question 5

In the eukaryotic genome:

Answer 5

Different cell types have different gene expression pattern

Chromatine is another level of gene regulation

Uncoupled transcription/translation

Question 6

In prokaryotes, transcription is mostly regulated on the level of

Answer 6

initiation

Question 7

What is necessary to activate the repressor?

Answer 7

Co-repressor

ex: Trp

Question 8

What is an inducible operon?

Answer 8

A gene segment that is already bound by a repressor, is able to bind an inducer which releases repressor from operon

*No inducer = No expression

Question 9

In the lac operon what is the inducing metabolite? Repressor?

Answer 9

allolactose

Glucose

*No lactose = no expression

*Lactose alone = no expression

*Requires allolactose + cAMP in order to achieve high (any) level of transcription*

Question 10

For eukaryotes genes must be in what to be expressed

Answer 10

active chromatin

*no operons- each gene has its own promoter

Question 11

In eukaryotes there is regulation at multiple levels

Answer 11

Chromatin: chromatin remodeling and gene rearrangement

Transcription: TFs affecting binding of RNA pol

Maturation of mRNA: processing of transcript

Translation: initiation of translation and mRNA stability

Question 12

What is the definition of epigenetics?

Answer 12

Changes in chromatin (histones or DNA) that can be inherited.

*Note: there is no change in the nucleotide sequence

Question 13

Why do we require chromatin remodeling

Answer 13

There will be no transcription if the promoter region is part of the nucleosome

Question 14

Gene expression is also affected by their

Answer 14

Rearrangements

Amplification

Deletion

Question 15

When a gene is actively transcribed only paternally or maternally inherited chromosome this is known as

Answer 15

genetic imprinting

Question 16

What are the 2 most common types of posttranslational modifications of histones?

Answer 16

Acetylation

Methylation

Question 17

Trimethylation of H3Lysine-9 attracts a a specifiv hetterochromatin called HP1 which:

Answer 17

Induces a spreading of Lysine-9 trimethylation followed by further HP1 binding => leading to siliencing of gene expression

Question 18

Histone acetyltransferases (HATs) acetylate histone tails. Acetylation of Lys amino acids reduces net positive charge, decreases histone-DNA interaction, and creates open chomatin or euchromatin. What is the purpose of HATs?

Answer 18

By creating open or eu-chromatin, one can surmise that acetylated histones are indactive of active gene expression

Question 19

In order to reverse the effects of HATs the active chromatin is converted into inactive chromtin via:

Answer 19

HDACs- histone deacetylases

Question 20

What are the 3 diseases associated with genetic imprinting

Answer 20

Angelman syndrome: inability to express UBE3A on paternally inherited chromosome 15; Caused by mutation or deletion(>) of maternal gene; paternally imprinted gene cannot be expressed

Prader willis syndrome: results from loss of genes that are active only on paternally inherited chromosome 15 (opposite to angelman syndrome); most cases caused by deletion of a region of paternal chromosome 15; minority of cases caused by maternal uniparental disomy (UPD)–> inheritance of 2 copies of chromosome 15 from mother

Russel-silver syndrome: dwarfism caused by imprinting error; most cases (chromosome 11) result from hypomethylation of maternally expressed H19 and paternally expressed IGF2 genes; few cases (chromosome 7) have both copies of inherited from mother UDP.

Question 21

What is the DNA base that accepts methyl groups resulting in posttranslational histone modification?

Answer 21

Cytosine

Question 22

Cancer cells show a global hpomethylation of genome. Why?

Answer 22

Hypermethylation- can silence tumor suppressor genes

Hypomethylation- can activate proto-onco genes cMYC and H-RAS

Question 23

Chromatin remodeling

Answer 23

A partial or complete displacement of nucleosomes from specific DNA sequences

Question 24

What is the first mechanism of chromatin remodeling?

Answer 24

Chromatin remodeling complexes => they unwind the DNA from nucleosome and require ATP

Question 25

What is the second mechanism of chromatin remodeling?

Answer 25

Covalent modification of histones:

HATs- create active chromatin by attaching acetyl group to Lysine residues in the tail of histones; the attachment of the acetyl group reduces the electrostatic interactions between histones and DNA

HDACs- create repressed chromatin (heterochromatin) by removing acetyl groups from histones

Question 26

Lipophilic hormones regulate transcription thru

Answer 26

Nuclear receptors

*NRs binds DNA regulatory sequence- hormone response element; can induce or repress transcription

* Nuclear localization signal is necessary for translocation into nucleus

-Steroid hormone receptors bind either corepressor or coactivators

Question 27

Activators, inducers, repressors, or nuclear receptors contain:

Answer 27

DNA binding domains

–>allow them to recognize and bind specific nucleotide sequences

–>DNA binding domains contaian a specific protein motif; ex: Zinc finger

Question 28

Where is a common loaction for a zinc finger bindnig domain?

Answer 28

estrogen receptor

–> contains zinc ion coordinated with 4 cysteine residues

*Nucleotide recognition signal (NRS) binds a specific base sequence in the major groove of DNA