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[OS 201] 3rd Exam > Trans - Regulation of Gene Expression > Flashcards

Flashcards in Trans - Regulation of Gene Expression Deck (78)
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2

Importance of regulation of gene expression (3), give examples of each

1. adaptation to environmental changes --> ex. memory B cell antibody production during immune response
2. development --> ex. pluripotential stem cells
3. differentiation of cells --> ex. specific proteins for specific cell function

3

Levels of eukaryotic gene regulation (6)

1. epigenetic control
2. transcriptional control
3. post-transcriptional control
4. RNA transport control
5. Translational control
6. Post-translational control

4

Heterochromatin vs Euchromatin

1. heterochromatin --> dense, transcriptionally silent, tightly packed, inaccessible to polymerases and other enzymes
2. euchromatin --> loosely packed and active in gene transcription

5

Define differential gene expression

Some genes are expressed while others are repressed

6

a) structure and b) significance of telomeres

a) complexes of DNA and proteins at the end of chromosomes
b) maintain structural integrity, prevent attack by nucleases, allow repair systems to differentiate between ends and breaks

7

Mechanisms to increase/decrease access to DNA sequence (2)

1. gene regulatory proteins
2. RNA polymerases

8

Mechanisms to alter chromatin structure (2)

1. cytidine methylation
2. histone methylation

9

Old and new concepts related to genetic switches

Old: "loss" of genesNew: genes can be turned "on" or "off"

10

Principle of DNA methylation

[1] Silencing genes to reduce unnecessary gene expression
[2] Methylation of CG dinucleotide (CpG) in promoter causes silencing of genes

11

Principle of DNA methylation

[1] Silencing genes to reduce unnecessary gene expression
[2] Methylation of CG dinucleotide (CpG) in promoter causes silencing of genes

12

CpG

Cytosine-phosphate-guanine

13

Characteristic of promoter region related to methylation

10-20x more CpG dinucleotides --> more affected by methylation

14

Effect of methylation on promoter

[1] High methylation / hypermethylation --> transcriptionally silent
[2] Low methylation / hypomethylation --> transcriptionally active

15

Other effects of methylation

Prevent binding of regulatory factors by stearic hindrance

16

Mediators of methylation

MeCP1 and MeCP2 (Methylated CpG binding proteins 1 & 2)

17

Fragile X syndrome

Mental retardation caused by expansion of CGG at 5' UTR of FMR1 gene --> increased methylation causing silencing of FMR and brain-specific mRNA during development

18

Histones

Order DNA into nucleosomes, (+) charged due to high lysine and arginine content --> form ionic bonds with (-) charged DNA

19

Principle of histone acetylation

Acetyl groups attached to lysine in histone, forming tails that protrude from the nucleosome --> repulsion between tails causes more open DNA structure

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Effect of histone acetylation

More acetylation --> more open DNA structure --> more accessible for transcription

21

Histone aminotransferases - function?

Eliminate positive charge on lysine, decreasing interaction of histone and negative DNA

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Histone deacetylases - function?

Restore positive charge of lysine, increasing interaction of histone and negative DNA

23

Relationship between DNA methylation and histone acetylation

Reciprocal --> when DNA is methylated, histone is deacetylated, and vice versa

24

Sites of histone methylation to hinder transcription

Histone H3 lysine 9, 27
Histone H4 lysine 2

25

Sites of histone methylation to enhance transcription

Histone H3 lysine 4, 27, 36

26

Effect of histone methylation

Activate or deactivate DNA, depending on methylation site

27

Ubiquitin - function?

Marks defective protein for destruction

28

Effects of histone ubiquitination

[1] disruption and spreading of chromatin allowing binding of transcription proteins;
[2] binding of effector proteins for other regulatory processes;
[3] allows other histone modifications to occur

29

Principle of histone ubiquitination

Attachment of ubiquitin to histone in order to modulate gene expression

30

Histone ubiquitination is required for these specific regulatory processes

di- and tri- methylation of H3 lysine 4 and lysine 79

31

Effects of histone phosphorylation

[1] chromatin condensation during mitosis;
[2] unknown effect on gene regulation