8. Transcription And Processing In Eukaryotes

Question 1

Post-transcriptional modifications (editing) of mRNA’s

Answer 1

Intron splicing

5’ capping

3’ poly-adenylation

Question 2

Differences in eukaryotic transcription

Answer 2

1. Harder to locate promoter
2. Transcription and translation are decoupled
3. Euk. DNA is wrapped up around proteins
4. Euk. Transcription is more complex

Question 3

RNA polymerase II

Answer 3

Transcribes mRNA and some functional RNA’s

Assisted by transcription factors

Question 4

Transcription factors

Answer 4

Protein complexes that help it recognize and initiate transcription at promoter

Question 5

Transcription initiation in eukaryotes

Answer 5

1. TFIID binds promoter at TATA box via TBP
2. Other transcription factors associate leading to the formation of pre-initiation complex
3. RNA polymerase starts synthesis & leaves the promoter & TFIID behind
4. Coupled to phosphorylation of RNA pol. At CTD

Question 6

TFIID

Answer 6

General transcription factor

Question 7

TATA box

Answer 7

Site of 1st event in transcription

Question 8

TBP

Answer 8

TATA binding protein

Attracts other GTF’s & RNA pol II core to promoter

Question 9

CTD

Answer 9

Carboxy terminal domain

Protein tail

Initiation ends after CTD has been phosphorylation by one of GTF’s

Question 10

Cotranscriptional processing of RNA during elongation

Answer 10

RNA processing (capping, splicing, and polyadenylation) happen as RNA’s are transcribed with help of RNA polymerase

Question 11

Capping

Answer 11

RNA processing proteins bind to RNA polymerase at CTD

Changes in phosphorylation on dif. CTD residues recruit dif. RNA processing proteins involved

Question 12

7-MG cap

Answer 12

1. Protects mRNA from nucleases

2. Recognition signal for translation machinery

Question 13

Splicing

Answer 13

Enzymes recruited by phosphorylation in CTD

Question 14

Poly (A) tail

Answer 14

1. Cleavage by endonuclease
   Mediates mRNA transport across the nuclear envelope
2. Addition of poly (A)tail by poly (A) polymerase enhances mRNA stability in cytoplasm

Question 15

Transcript one complexity

Answer 15

Does not reflect in an increase in the number of genes

Question 16

Explain protein diversity w/ limited # of genes

Answer 16

Explained by splicing & generation of alternative transcripts

Complex organisms also have more introns per gene

Question 17

Alternative splicing

Answer 17

Produces related but distinct protein isoforms