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MD2S3: Molecular Biology > Transcription in Eukaryotes > Flashcards

Transcription in Eukaryotes Flashcards

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1
Q

What are the differences between Prokaryotic and Eukaryotic transcription?

A

Chromatin Structure
Three distinct RNA Polymerases
Transcription Factors
Eukaryotic Promotors
Regulatory Elements and Activators
Enhancers
Post-Transcriptional Modifications of RNA Molecules
mRNA Splicing
mRNA Editing

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2
Q

Actively transcribed areas of DNA are called …

A

Euchromatin

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3
Q

Inactive Segments of DNA are called …

A

Heterochromatin

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4
Q

Conversion between forms of chromatin is called …

Forms of chromatin refers to euchromatin and heterochromatin

A

Chromatin Remodeling

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5
Q

Chromatin Remodeling
Mechanism of Chromatin Remodeling

A

Covalent modification of histone

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6
Q

Chromatin Remodeling
Acetylation is catalysed by …

A

Histone Acetyl Transferases (HATs)

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7
Q

Chromatin Remodeling
Acetylation causes …

A

elimination of positive charge of lysine which decreases interactions of chromatin

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8
Q

Chromatin Remodeling
Deacetylation is catalysed by …

A

Histone Deactylases (HDACs)

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9
Q

What are the three types of RNA Polymerases?

A

RNA Polymerase I
RNA Polymerase II
RNA Polymerase III

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10
Q

Polymerase Types
RNA Polymerase I Function

A

Synthesis of rRNA subunits (28S, 18S and 5.8S)

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11
Q

Polymerase Types
RNA Polymerase II Function

A

Synthesizes mRNA
Synthesizes snRNA

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12
Q

Polymerase Types
RNA Polymerase III Function

A

Synthesizes tRNA
Synthesizes 5S rRNA
Syntheizes snRNAs

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13
Q

How many types of Polymerases does Mitochondria contain?

A

1

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14
Q

Promoters of RNA Polymerase II
Names

A

TATA Box (-25bp from transcription start)
Initiator (Inr)
Downstream Promoter Elements (DPE)

TATA Boxes are less common than the other two

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15
Q

Promoters of RNA Polymerase II
Others names for promoters

A

Cis-acting elements

Because they are on the same molecule of DNA as the gene being transcribed

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16
Q

Promoters of RNA Polymerase II
What binds to cis-acting elements?

A

Proteins called General Transcription Factors (GTFs)

Interact with each other and RNA Polymerase II

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17
Q

GTFs
Function of GTFs

A

Assembly of Transcription Initiation Complex at Promoter
Determination of which gene is transcribed

Each RNA Polymerase has its own transcription factors

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18
Q

GTFs
When can GTFs bind to the DNA Sequence?

A

When it is decondensed

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19
Q

GTFs
What GTFs are required for initiation?

A

TFIID
TFIIF
TFIIH

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20
Q

GTFs
TFIID Function

A

Contains TATA-binding protein and TATA-associated factors
Recognizes and binds TATA boxes

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21
Q

GTFs
TFIIF Function

A

Bring Polymerase to Promoter

22
Q

GTFs
TFIIH Function

A

Melts DNA

23
Q

Regulatory Elements
What are Regulatory Elements?

A

Regulatory Sequences upstream of promoter

24
Q

Regulatory Elements
What are the types of Regulatory Elements?

A

Proximal Regulatory Elements
Distal Regulatory Elements/Enhancers

25
Q

Regulatory Elements
What proteins can bind to Regulatory Elements?

A

Specific Transcription Factors (STFs)/Transcriptional Activators

26
Q

Regulatory Elements
When STFs bind to proximal promoter elements …

A

regulates frequency of transcription initiation

27
Q

Regulatory Elements
When STFs bind to distal promoter elements …

A

mediates response to hormones

28
Q

Regulatory Elements
What are the two binding domains of STFs?

A

DNA-Binding Domain
Transcription Activation Domain (recruits GTF and HAT)

29
Q

Enhancers
Function

A

DNA sequences increasing rate of initiation of transcription

30
Q

Enhancers
Location

A

Upstream or downstream of transcription start site
Can occur near or far from promoter
Can occur on either DNA strand

31
Q

Enhancers
Which DNA sequences of Enhancers can bind STF?

A

Response Elements

32
Q

RNA Polymerase II is inhibited by …

A

α-Amanitin

Toxin produced by mushrooms

33
Q

What is the Transcription Unit?

A

DNA Segment between Initiation and Termination Sequences

34
Q

rRNA synthesis and modification

A

Generated from long precursor pre-rRNA
28S, 18S and 5.8S synthesized from single pre-rRNA
5S synthesized by RNA Polymerase III
Cleaved by Ribonucleases

35
Q

tRNA modification

A

-CCA sequences addition to 3’-OH end by nucleotidyl-transferase

36
Q

mRNA modification

A

Addition of 5’ cap
Addition of 3’-poly-A tail
Splicing

37
Q

mRNA modification: 5’-cap
Process

A

Terminal Guanine methylated in Cytosol by Guanine-7-Methyltransferase

38
Q

mRNA modification: 5’-cap
Source of methyl-group

A

S-Adenosylmethionine

39
Q

mRNA modification: 5’-cap
Function of 5’-cap

A

Stabilizes mRNA
Permits Efficient Initiation
Protects 5’-end

40
Q

mRNA modification: Poly-A-tail
Which enzyme catalyses addition of Poly-A-tail?

A

Polyadenylate Polymerase

41
Q

mRNA modification: Poly-A-tail
Function

A

Stabilize mRNA
Facilitate Exit from Nucleus
Aids in Translation

42
Q

mRNA modification: Splicing
Complex responsible for splicing

A

Spliceosome

43
Q

mRNA modification: Splicing
How is Splicing mediated?

A

Mediated by 5 snurps: U1, U2, U4, U5 and US

snurps = Small Nuclear Ribonucleoprotein Particles

44
Q

mRNA modification: Splicing
What are U1, U2, U4, U5 and US?

A

Small Nuclear RNA associated with Proteins

45
Q

mRNA modification: Splicing
Function of snurps

A

Removal of introns by base pair formation with consensus sequences at intron ends

46
Q

mRNA modification: Splicing
Procedure

A

2’-OH group of adenine (branch site A) of intron attacks phosphate at 5’-end of intron (splice donor site)
Forms 2’-5’-phosphodiester bond called Lariat Structure
3’-OH of exon 1 attack 5’-phosphate at splice acceptor site forming phosphodiester bond between exon 1 and 2

47
Q

mRNA modification: Splicing
Fate of the Lariat Structure

A

Degraded
Used as precursor for ncRNA such as snoRNA

48
Q

mRNA modification: Splicing
What may splice site mutation cause?

A

Improper Splicing
Synthesis of Abnormal Proteins

49
Q

mRNA modification: Splicing
Example of splice site mutation

A

β-thalassemia

50
Q

mRNA modification: Splicing
Alternative Splicing produces …

A

protein isoforms

MD2S3: Molecular Biology (10 decks)

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