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Genetics > Transcription And Its Regulation In Eukaryotes > Flashcards

Transcription And Its Regulation In Eukaryotes Flashcards

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1
Q

Steps of transcription in eukaryotic cells :

A

1.initiation 2. Elongation 3. Termination

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2
Q

Transcription mainly occurs by an enzyme that it is called :

A

RNA polymerase

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3
Q

The three types of RNA polymerase:

A

RNA polymerase 1 , RNA polymerase 2 , RNA polymerase 3 , Mitochondrial RNA polymerase

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4
Q

RNA POLYMERASE 1

A

Transcribes 18S , 5.8S , 28S ribosomal RNA genes.

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5
Q

RNA POLYMERASE 2

A

Transcribes mRNA and most small nuclear RNAs

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6
Q

RNA POLYMERASE 3

A

Transcribes tRNA , 5S rRNA , some small nuclear RNA.

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7
Q

Mitochondrial RNA polymerase

A
  1. Responsible for mitochondrial gene expression
    2.Providing RNA primers for initiation of replication of the mitochondrial Genome .
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8
Q

Mitochondrial RNA polymerase resembles :

A

Bacterial RNA polymerase

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9
Q

Initiation definition

A

Binding of RNA polymerase to the promotor region

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10
Q

RNA polymerase 2 core promoter definition :

A

Minimal set of sequence elements required for accurate transcription initiation by polymerase 2 machinery , is typically about 40-60 nucleotide long extending either upstream or downstream from the transcription start site

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11
Q

What are the sequence elements of core polymerase 2 promoter ?

A

1) TFIIB recognition element (BRE)
2) TATA element
3) initiator (Inr)
4) the downstream promoter elements ( DPE,DCE,MTE )

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12
Q

Why is the promoter important?

A

It serves as a binding platform for the transcription machinery ( GTFs and pol II )

GTFs : general transcription factors

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13
Q

Importance of General transcription factors (GTFs) :

A

1) help polymerase bind to the promoter & melt the DNA
2) help the polymerase escape from the promotor and embark on the elongation phase

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14
Q

Initiation steps :

A
  1. Formation of pre- initiation complex
  2. Promoter melting
  3. Promoter escaping
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15
Q

What is the pre-initiation complex and where it is formed :

A

Pre-initiation complex (GTFs & Pol II ) bound together at the promoter

GTFs : refer to the GENERAL TRANSCRIPTION FACTORS

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16
Q

Binding to the promoter region mainly depends on :

A

TFIID ( transcription factor type D )

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17
Q

TFIID definition and components :

A

It’s a general transcription factor and a multi-subunit complex:
1)TBP ( TATA binding Proteins)
2) TAFs (TBP-associated factors )

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18
Q

TBP Function :

A

Recognises the TATA element and binds to that box
“The strongest binding “

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19
Q

TAFs Function :

A

Recognises other core promoter elements such as Inr , DPE , DCE

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20
Q

So , ………………. Is critical factor in promoter recognition and preinitiation complex establishment

A

TFIID

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21
Q

TBP-DNA complex importance :

A

It is the platform to recruit other general transcription factors and Pol II itself to the promoter.

In the following order ( TFIIA, TFIIB, TFIIF with the polymerase THEN TFIIE and TFIIH ) .
TFII F brings the RNAP II to the promoter site

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22
Q

Melting of the Promoter :

A

It requires hydrolysis of ATP and is mediated by TFIIH

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23
Q

Promoter escape requires :

A

1)ATP hydrolysis ( additionally to the ATP hydrolysis needed for DNA melting )
2) Phosphorylation of the polymerase

24
Q

About the phosphorylation of polymerase (activation of Pol II ) :

A

The large subunit of Pol II has a carboxyl-terminal domain (CDT ) , which contains a series of repeats ( Tyr-Syr-Pro-Thr-Ser-Pro-Ser ) repeated 52 times . Each repeat contains sites of phosphorylation by specific Kinases as TFIIH .

25
Q

About TFIIH : it has two functions

A

it is a ten-subunit protein

1) mediates ATP hydrolysis in promoter melting
2) phosphorylation of CTD region in promoter escaping

26
Q

The transcription process :

A
  1. Release of TFII A,B,E,H
  2. (Pol II - TF II F) Complex leaves the promoter and starts transcription until the termination signal is reached
    3.Dissociation of the complex
  3. Dephosphorylation of the complex by a phosphates
27
Q

Termination in eukaryotes :

A

Dissociation of the complete transcript & release of RNA polymerase from the template DNA

28
Q

The process that differs for each of the three RNA polymerase :

A

The termination process

29
Q

Mechanism of termination :

A
  1. CPSF and CSTF recognise the poly-A signal in the transcribed RNA and bind there
  2. Poly-A-bound CPSF and CSTF recruit other proteins to carry out RNA cleavage and then polyadenylation
  3. Formation of primary transcript
30
Q

CPSF & CSTF :

A

CPSF :cleavage and polyadenylation specifies factor
CSTF : cleavage stimulation factor
They are carried by the CTD

31
Q

Poly-A polymerase :

A

Adds 200 adenine to the cleaved 3’ end of the RNA without a template

32
Q

……………….. is unique to transcripts made by Pol II :

A

The long poly-A

33
Q

Processing of mRNA
(Post transcription modifications )

A

1) 5’ capping
2) addition of Poly(A) tail
3) Removal of introns and splicing of exons.

34
Q

What is the Cap ?

A

7- methylguanosine triphosphate attached to the 5’ end of the mRNA

35
Q

Importance of capping :

A

1)protects the 5’ end of the mRNA from 5’ exonuclease enzyme
2)helps its recognition by the ribosome
3)helps the initiation of protein synthesis
4) Eukaryotic mRNA lacking the cap are not efficiently translated
5) helps transport of mRNA to the cytoplasm

36
Q

What happens is :

A

1) formation of 5’-5’ unusual triphosphate linkage
2) Methylation ( primary and secondary )

37
Q

Unusual ( 5’-5’ ) triphosphate linkage formation :

A

1) one of the terminal phosphate group of mRNA chain is removed by RNA triphosphatase , leaving a bisphosphate group
2) GTP is added to the terminal bisphosphate by mRNA guanylyltransferase , losing a pyrophasphate from GTP substrate in the process
3) (5’-5’) unusual triphosphate linkage

38
Q

Primary Methylation :

A
  • Occurs in the Nucleus
  • it is catalysed by guanine-7-methyl transferase
    Using (SAM) as a source of methyl group
  • this process occurs on the N-7 of guanine of the GTP cap

SAM = S adenosylmethionine = active methionine

39
Q

Secondary Methylation :

A
  • occurs in the cytoplasm
  • either on 2’ OH of ribose of some nucleotides
    OR
    At N-6 of adenine of some nucleotides
40
Q

Addition of poly A tail is linked with the ………….

A

Termination of transcription

41
Q

Addition of poly A tail :

A
  • A poly-A tail is added at the 3’ end of mRNA after the mRNA is cleaved (15-20) nucleotides downstream from the AAUAAA recognition sequence , the poly A tail immediately binds several copies of apply A binding proteins

Poly A binding proteins protect mRNA against 3’ exonuclease

42
Q

Poly-A definition :

A

It is about 100-200 A bases that is not transcribed from DNA but added after transcription by the enzyme polyadenylate polymerase using ATP as a substrate

43
Q

Importance of Poly A tail :

A
  • stabilises the mRNA
  • protects it from exonuclease enzymes
  • increases the efficiency of translation
  • facilitates their exit from the nucleus
44
Q

The length of poly (A) tail determines the …………

A

Half time of mRNA

45
Q

After the poly-A tail enters the cytoskeleton , the poly A tail …………….

A

Gradually shortened

46
Q

Removal of introns and splicing of exons definition :

A

Excision of introns and joining the ends of exons

47
Q

What determines the site of splicing is :

A

The sequence of bases at the exon-intron junction

48
Q

The reason of splicing existence is :

A

Leave only the functional mRNA molecule

49
Q

Splicing process occurs in the …………. By the help of ………………..

A

Nucleus ,snRNP

50
Q

About snRNP :

A
  • Refers to the small nuclear ribonucleoproteins
  • other name is snurps
  • composed of small nuclear RNA ( snRNA ) and proteins.
    -Ones that acting on mRNA are called spliceosomes ( Catalytic RNAs or RNA enzymes , termed as ribozymes )
51
Q

Advantages for having protein-coding genes organised as exons and introns:

A

1) Alternative Splicing
2) Decreasing the possibility of effective mutations

52
Q

Decreasing the possibility of effective mutations :

A

If the mutations occur at the regions of introns , it is NOT effective

53
Q

Alternative splicing OR differential splicing

A

It is a regulated process during gene expression that results in a single gene coding for multiple proteins in which particular exons of a gene may be included within or excluded from the mRNA

54
Q

Synthesis and processing of rRNA :

The primary transcript of rRNA include :

A

1) 45S rRNA ( pre-RNA , produces three types of rRNA )
2) 5S rRNA

55
Q

The 45S rRNA is Sunthesized by …………. And then ……………….. in the …………….. which cleaves the ……………… to realease ……………..

A

RNA polymerase I , undergoes RNA processing , nucleus , precursor , the mature 18S/5.8S/28S rRNA

56
Q

The 45S genes are ……………. Meaning that ……………

A

Clustered together and tandemly repeated, one copy each of 18S, 5.8Sand 28S occur , followed by untranscribed spacer DNA then another set occur

57
Q

The 5S rRNA genes are transcribed by ………………. In the ……………….. outside of the ………….

A

RNA polymerase III , nucleoplasm , nucleolus

Genetics (3 decks)

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