Transcription in Eukaryotes

Question 1

What are the differences between Prokaryotic and Eukaryotic transcription?

Answer 1

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

Question 2

Actively transcribed areas of DNA are called …

Answer 2

Euchromatin

Question 3

Inactive Segments of DNA are called …

Answer 3

Heterochromatin

Question 4

Conversion between forms of chromatin is called …

Forms of chromatin refers to euchromatin and heterochromatin

Answer 4

Chromatin Remodeling

Question 5

Chromatin Remodeling
Mechanism of Chromatin Remodeling

Answer 5

Covalent modification of histone

Question 6

Chromatin Remodeling
Acetylation is catalysed by …

Answer 6

Histone Acetyl Transferases (HATs)

Question 7

Chromatin Remodeling
Acetylation causes …

Answer 7

elimination of positive charge of lysine which decreases interactions of chromatin

Question 8

Chromatin Remodeling
Deacetylation is catalysed by …

Answer 8

Histone Deactylases (HDACs)

Question 9

What are the three types of RNA Polymerases?

Answer 9

RNA Polymerase I
RNA Polymerase II
RNA Polymerase III

Question 10

Polymerase Types
RNA Polymerase I Function

Answer 10

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

Question 11

Polymerase Types
RNA Polymerase II Function

Answer 11

Synthesizes mRNA
Synthesizes snRNA

Question 12

Polymerase Types
RNA Polymerase III Function

Answer 12

Synthesizes tRNA
Synthesizes 5S rRNA
Syntheizes snRNAs

Question 13

How many types of Polymerases does Mitochondria contain?

Answer 13

1

Question 14

Promoters of RNA Polymerase II
Names

Answer 14

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

TATA Boxes are less common than the other two

Question 15

Promoters of RNA Polymerase II
Others names for promoters

Answer 15

Cis-acting elements

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

Question 16

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

Answer 16

Proteins called General Transcription Factors (GTFs)

Interact with each other and RNA Polymerase II

Question 17

GTFs
Function of GTFs

Answer 17

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

Each RNA Polymerase has its own transcription factors

Question 18

GTFs
When can GTFs bind to the DNA Sequence?

Answer 18

When it is decondensed

Question 19

GTFs
What GTFs are required for initiation?

Answer 19

TFIID
TFIIF
TFIIH

Question 20

GTFs
TFIID Function

Answer 20

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

Question 21

GTFs
TFIIF Function

Answer 21

Bring Polymerase to Promoter

Question 22

GTFs
TFIIH Function

Answer 22

Melts DNA

Question 23

Regulatory Elements
What are Regulatory Elements?

Answer 23

Regulatory Sequences upstream of promoter

Question 24

Regulatory Elements
What are the types of Regulatory Elements?

Answer 24

Proximal Regulatory Elements
Distal Regulatory Elements/Enhancers

Question 25

**Regulatory Elements** What proteins can bind to Regulatory Elements?

Answer 25

Specific Transcription Factors (STFs)/Transcriptional Activators

Question 26

**Regulatory Elements** When STFs bind to proximal promoter elements ...

Answer 26

regulates frequency of transcription initiation

Question 27

**Regulatory Elements** When STFs bind to distal promoter elements ...

Answer 27

mediates response to hormones

Question 28

**Regulatory Elements** What are the two binding domains of STFs?

Answer 28

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

Question 29

**Enhancers** Function

Answer 29

DNA sequences increasing rate of initiation of transcription

Question 30

**Enhancers** Location

Answer 30

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

Question 31

**Enhancers** Which DNA sequences of Enhancers can bind STF?

Answer 31

Response Elements

Question 32

RNA Polymerase II is inhibited by ...

Answer 32

α-Amanitin ## Footnote Toxin produced by mushrooms

Question 33

What is the Transcription Unit?

Answer 33

DNA Segment between Initiation and Termination Sequences

Question 34

rRNA synthesis and modification

Answer 34

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

Question 35

tRNA modification

Answer 35

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

Question 36

mRNA modification

Answer 36

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

Question 37

**mRNA modification: 5'-cap** Process

Answer 37

Terminal Guanine methylated in Cytosol by Guanine-7-Methyltransferase

Question 38

**mRNA modification: 5'-cap** Source of methyl-group

Answer 38

S-Adenosylmethionine

Question 39

**mRNA modification: 5'-cap** Function of 5'-cap

Answer 39

Stabilizes mRNA Permits Efficient Initiation Protects 5'-end

Question 40

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

Answer 40

Polyadenylate Polymerase

Question 41

**mRNA modification: Poly-A-tail** Function

Answer 41

Stabilize mRNA Facilitate Exit from Nucleus Aids in Translation

Question 42

**mRNA modification: Splicing** Complex responsible for splicing

Answer 42

Spliceosome

Question 43

**mRNA modification: Splicing** How is Splicing mediated?

Answer 43

Mediated by 5 snurps: U1, U2, U4, U5 and US ## Footnote snurps = Small Nuclear Ribonucleoprotein Particles

Question 44

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

Answer 44

Small Nuclear RNA associated with Proteins

Question 45

**mRNA modification: Splicing** Function of snurps

Answer 45

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

Question 46

**mRNA modification: Splicing** Procedure

Answer 46

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

Question 47

**mRNA modification: Splicing** Fate of the Lariat Structure

Answer 47

Degraded Used as precursor for ncRNA such as snoRNA

Question 48

**mRNA modification: Splicing** What may splice site mutation cause?

Answer 48

Improper Splicing Synthesis of Abnormal Proteins

Question 49

**mRNA modification: Splicing** Example of splice site mutation

Answer 49

β-thalassemia

Question 50

**mRNA modification: Splicing** Alternative Splicing produces ...

Answer 50

protein isoforms