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Flashcards in control of gene expression 1 Deck (41):
1

why if most cells in organisms contain the same DNA are cells so different

due to only a subset of genes being transcribed at any time in a particular cell

2

TATA box

- a DNA sequence that indicates where a genetic sequence can be read and decoded--> a type of promotor sequence The TATA-binding protein (TBP) is a general transcription factor that binds specifically to a DNA sequence called the TATA box. This DNA sequence is found about 30 base pairs upstream of the transcription start site in some eukaryotic gene promoters.

3

example of a promotor sequence

TATA BOX

4

control of transcription initiation

--> polymerase interacts with the proteins when it binds to the promotor region- found int he control region - e.g. TATA box--> allows it to bind and start transcription.

5

process of initiation in eukaryotes

-TF bind to promotor sequences and forms the basal transcription complex with RNA pol 2

-activator proteins bind upstream the enhance sequences and interact with the basal transcription complex

6

without transcription factors (which attach to TATA boxes), RNA polymerase 2 cannot..

bind to promotors

7

cis- acting element

operator -influences expression of genes downstream from it on the same 2 stranded DNA -enhancer upstream from activating sequence -includes promoter very close to the protein coding region and includes the nitration site, where transcription begins and a 'TATA box'

8

trans acting regulatory gene

repressor -influences expression of any relevant gene in the same cell, on the same or diff DNA

9

hows many different RNAs are there that transcribe diff sets of genes in eukaryotes

3

10

RNA polymerase 1

5.85, 185, 285 rRNA gene

11

RNA polymerase 2

all protein coding genes, plus snoRNA gene, miRNA genes, siRNA genes and most snRNA genes

12

RNA polymerase 3

tRNA genes, 5s rRNA genes, some snRNA genes and been for there small RNA

13

what are rRNA named according to

their s value- refers to rate of sedimentation in an ultracentrifuge--> the larger the s value, the larger the rRNA

14

what inhibits RNA polymerase 2

alpha-amanitin- from mushrooms -deadly

15

epigenetic inheritance

was first used to refer to the complex interactions between the genome and the environment that are involved in development and differentiation in higher organisms. Today, this term is used to refer to heritable alterations that are not due to changes in DNA sequence. ep

16

what interact with basal transcription complex

activator proteins

17

multiple epigenetic mechanisms can contribute to stable gene repression: state 2

-histone modification -DNA methylation

18

how does epigenetic mechanisms contribute to stable repression

epigenetic modifications, or “tags,” such as DNA methylation and histone modification, alter DNA accessibility and chromatin structure, thereby regulating patterns of gene expression.

19

EPIGENENTIC changes are usually..

erased turring formation of germ cells e.g. an individual could be born with gene Y on; however due to chromatin changes it could be switched off. During the multiplication of somatic cells, the chromatin changes are followed through, so gene Y is switched off. However during the producing of germ cells the epigenetic change will not be passed on and gene Y will be on.

20

formation of the basal transcription complex

1. TATA-box binding protein (TBP) binds to the TATA box 2. TBT recruits TFIID complex and the TFIIB to the promotor region 3. RNA polymerase 2 and further transcription factors bind tot he promotor to form the BASAL TRANSCRIPTION COMPLEX

21

what gene control does methylation and histone modification have

histone modification and direct dna methylation on cytosine helps maintain patterns of gene repression in somatic cells

22

4 points on bacterial gene expression

  • no nuclear mem
  • one cytoplasmic compartment
  • no histones
  • couples transcription and translation

23

protein synthesis in bacteri

where transcription and translation take place at the same time in the cytoplasm

24

an operon..

has ONE PROMOTER All genes on that operon are transcribed together mRNA is translated to give separate structures

25

examples of how a galactose gene may be switched off

Regulation of a Lac operon -if lac repressor is present and there is no lactose then the lac repressor will bind to the operon that had DNA coding for proteins involved in the metabolism of lac. This prevents RNA polymerase from transcribing the DNA, so no b-Galactosidase activity. however If lactose is added, then it forms a complex with the lac repressor since it is complementary, This means the lac suppressor can no longer bind to the DNA and RNA polymerase is free to transcribe the DNA--> therefore when translation occurs proteins needed to metabolise lactose are produced

26

is lactose is not present...

if lac repressor is present and there is no lactose then the lac repressor will bind to the operon that had DNA coding for proteins involved in the metabolism of lac. This prevents RNA polymerase from transcribing the DNA, so no b-Galactosidase activity.

27

if lactose is not present..

If lactose is added, then it forms a complex with the lac repressor since it is complementary, This means the lac suppressor can no longer bind to the DNA and RNA polymerase is free to transcribe the DNA--> therefore when translation occurs proteins needed to metabolise lactose are produced

28

if lactose is present..

If lactose is added, then it forms a complex with the lac repressor since it is complementary, This means the lac suppressor can no longer bind to the DNA and RNA polymerase is free to transcribe the DNA--> therefore when translation occurs proteins needed to metabolise lactose are produced

29

lac repressor

a gene regulatory protein in bacteria

30

Gal4

a gene regulatory protein in yeast -a typical model for eukaryotic gene regulation

31

Gal 4 system: a paradigm for eukaryotic gene regulation

-when there is no Galactose present Gal80 forms aa complex with Gal4 in the UASg part of the polypeptide chain--> therefore Gal80 acts as an inhibitor and there is no transcription of GAL 1 however -when galactose is added, it attaches t Gal80 and this means that Gal 80 ins' able to bind to Gal4. Therefore RNA pol is able to associate with the promoter region and transcription of GAL1 is initiated

32

How do chromatin structures play a role in eukaryotic gene regulation

when chromatin is condensed the gene is switched off--> however when activators decondenses the chromatin, the gene will be switched on due to RNA polymerase and TF being able to attach to promotor regions and start transcription

33

DNA is made accessible to transcription factors by multiple mechanisms:

first chromatin remodelling complex plays a role in all mechanisms accept histone modifying enymes

 

1.histone chaperones- cause histone removal and therefore transcription

2. Histone chaperon cause histone replacement and then transcription

3.Histone modifying enzymes cause specific histone modifcation 

34

DNA can also be covalently modified directly

in vertebrates thic can occur in the CG sequence. 

 

METHYLATED DNA REPRESSES GENE EXRESSION

35

what maintains patterns of gene repression in diffrenttiated cells

 

Cytosine methylation patterns can be inherited after DNA replication. E.g. epigenetic inheritance

 

36

Cytosine methylation patterns can be..

inherited after DNA repliation e.g. epigentic inheritance 

 

maintains patterns of gene repression  in diffrentiated cells

37

DNA can also be covalently modified directly

in vertebrate this can occur in the sequence CG.

-Methylate DNA represses gene expression

38

when a chromatin is condensed the gene is 

switched off 

39

core histones can be 

covalently modifed on their N terminal tails and also at many sites

40

activators can .. chromatin meaning:

activaotrs can decondense chromatin and cause a geent o turn on due to the RNA polymerase and TF being able to attach to the promoto regions

41

how can N temrinals on core histones be modfed

methylation

acetylation 

phosphorylation

upiquitylation