RNA Synthesis: Transcription

Question 1

What is RNA a key component in?

Answer 1

• Synthesis of proteins
• Splicing of genes
• Transfer of genetic information from nucleus to cytoplasm

Question 2

What is the most abundant RNA in cells?

Answer 2

rRNA

Question 3

What are the similarities in DNA and RNA synthesis?

Answer 3

• Need a template
• 5’ to 3’ polarity
• Proceeds in 3 phases

Question 4

What are the differences between DNA and RNA synthesis?

Answer 4

• RNA Pol needs no primer
• Only genes in DNA gets transcribed
• RNA is complimentary to one DNA strand

Question 5

Where is Transcription initiated and ended?

Answer 5

Initiated at promoters and ends at terminators

Question 6

What binding site do promoters recognise?

Answer 6

Sigma 70

No proofreading activity but can pause

Question 7

What binding site is recognised by the RNA Pol sigma subunit?

Answer 7

TATA box

Question 8

What are the steps for Initiation and Elongation in Transcription?

Answer 8

1. Polymerase binds promoter
* Close complex
* DNA still inact
2. Transcription bubble forms
* Open complex
* DNA unwinds over 12-15 bases
3. Transcription starts
* Promoter clearance
* Elongation
* Sigma dissociates
* Proceeds to termination

Question 9

What are the TWO ways in which transcription is terminated?

Answer 9

1. Rho-independent transcription
2. Rho-dependent transcription

Question 10

What happens in Rho-Independent termination?

Answer 10

1. Terminator sequence (pallindrome) causes hairpin in RNA and disrupts the RNA-DNA hybrid
2. Conserved polyA sequence in DNA generates polyA=U at end of RNA which is unstable so dissociates

Question 11

What happens in Rho-Dependent termination?

Answer 11

1. Polymerase pauses at termination site
2. Rho helicase binds to RNA
3. Associates with Rho utilisation element (Rut)
4. Faciltates dissociation of RNA

Question 12

What are the THREE polymerases used in Eukaryotic transcription and their roles?

Answer 12

1. Pol I: synthesis of pre-ribosomal RNA
2. Pol II: synthesis of mRNAs and ncRNA
3. Pol III: synthesis of tRNAs and ncRNAs

Question 13

Where is the TATA box located in many Pol II promoters?

Answer 13

-30

Question 14

How many subunits does RNA Pol II have?

Answer 14

12

Question 15

What are the phases of Transcription?

Answer 15

• Assembly
• Initiation
• Elongation
• Termination

Question 16

Which polymerase do Transcripton Factors (TFs) associate with?

Answer 16

Pol II at DNA

Question 17

What are the proteins required for Elongation?

Answer 17

• ELL
• PTFB
• SII (TFIIs)
• Elongin

Act to ensure transcription proceeds and to prevent pausing by the Pol II TFIIH complex

Question 18

What are the steps for Eukaryotic Pol II Transcription?

Answer 18

1. Assembly of Pol II complex subunits at promoter
2. Initiation: TFIIH kinase phophorylates Pol II on C terminal domain (CTD)
3. Elongation factors assist Pol II
4. Termination factors stop transcription

Question 19

Which antibiotics intercalates in DNA and inhibits polymerase?

Answer 19

Actinomycin D & Acridine

Question 20

Which antibiotic binds to the beta subunit of bacterial polymerases?

Answer 20

Rifamycin

Question 21

Which antibiotic from Amanita phalloides inhibits RNA Pol II?

Answer 21

α-amantin