RNA Processing

Question 1

Where does initiation occur in transcription

Answer 1

At the promoter - RNA polymerase binds to promoter + begins to unwind DNA

Question 2

What is a TATA box

Answer 2

DNA sequence within the promoter region of DNA

Question 4

What are transcription factors

Answer 4

Proteins that bind to DNA + influence transcription

Question 5

Where does a TATA box lie

Answer 5

25 nucleotides upstream from transcriptional start point

Question 6

How does RNA polymerase bind to DNA using the TATA box and transcription factors

Answer 6

• one transcriptional factor ( TF) recognises TATA box and binds
• more transcriptional factors recognise bound TF and bind
• RNA polymerase recognises TFs and binds to DNA in correct position + orientation
• additional TFs bind to DNA with RNA polymerase = transcription initiation complex
• RNA polymerase unwinds DNA double helix and RNA synthesis begins

Question 7

When is RNA transcript released from template

Answer 7

When RNA polymerase reaches the termination site

Question 8

What is the polyadenylation signal sequence and what does it doe to mRNA

Answer 8

• DNA sequence (AAUAAA) within the termination site region of DNA which codes for the signal in mRNA
• an enzyme recognises the signal and releases mRNA from RNA Polymerase

Question 9

Why does RNA need to be modified in eukaryotes

Answer 9

Movement into next chamber without being degraded

Question 10

What are the additions to mRNA ends in RNA processing

Answer 10

• 5’ (GTP) added to end of pre-mRNA during elongation in transcription so nothing is degraded
• 3’ tail (100-300 adenine nucleotides) added after mRNA transcript has been released from RNA polymerase

Question 11

Why is the addition of a 5’ cap mRNA important

Answer 11

• facilitates bonding of mRNA to an enzyme for translation
• protects mRNA from being digested by ribonucleases

Question 12

Why is the addition of a 3’ tail to mRNA important

Answer 12

• export mRNA from nucleus to cytoplasm for translation
• mRNA stability from degradation

Question 13

Why are introns removed from pre-mRNA in splicing

Answer 13

They don’t code for protein so removed from pre-mRNA before mRNA moves into the nucleus dor translation

Question 14

What proteins perform the splicing

Answer 14

Small nuclear ribonucleoproteins (snRNPs)

Question 15

Describe simply the process of splicing introns out

Answer 15

• snRNPs bind to consensus sequence near the 5’ and 3’ splice sites
• snRNPs join together to form spliceosome
• introns loop out
• spliceosome cuts pre-mRNA at introns/exon boundary

Question 16

Describe the process of RNA processing in detail

Answer 16

• a cut is made between 5’ Exon and intron = introns forms a closed loop
• the free 3’ OH group at the end of cut exon reacts with the 5’ phosphate of other exon
• 3’ Exon cleaved and splice to 5’ Exon = mature mRNA
• the excised intron is degraded in the nucleus