26. ELONGATION

Question 1

1. What happens during Transcription Elongation?

Answer 1

• there is the untwisting of the double helix
• this happens at 10 to 20 DNA bases at a time
• the nucleotides are added to the 3’ end of the RNA
  strand
• this is because the RNA strand always goes in the 5’-3’
  direction

Question 2

2. How many nucleotides are added in a second in Eukaryotes?

Answer 2

• 40 nucleotides per second

Question 3

3. How can we produce large amounts of protein in a specific time period?

Answer 3

• a gene can be transcribed simultaneously by several
  RNA polymerases

Question 4

4. How does the Termination of Transcription happen in Bacteria?

Answer 4

• the RNA Polymerase stops transcription
• it does this at the end of the Terminator
• this is the transcription termination point of the RNA
  sequence
• the mRNA is translated without being processed
• translation can start before transcription has ended

Question 5

5. How does the Termination of Transcription happen in Eukaryotes?

Answer 5

• the RNA Polymerase II transcribes a
  Polydenylation Signal (AAUAAA)
• the RNA Transcript (Strand) is released 10-35
  nucleotides after the Polydenylation Signal

Question 6

6. What do Eukaryotic cells do before Translation?

Answer 6

• they modify the RNA transcript
• this is called the Primary RNA transcript (pre-mRNA)

Question 7

7. What happens after this modification and processing?

Answer 7

• the mature mRNA is transferred to the cytoplasm

Question 8

8. What three steps does RNA processing consist of?

Answer 8

1. Addition of the 5’ Cap
2. Addition of the poly- A tail at the 3’ end
3. RNA Splicing

Question 9

9. What is the 5’ Cap?

Answer 9

• this is a modified guanine nucleotide (m⁷G)
• it is added to the 5’ end

Question 10

10. What is a poly- A tail?

Answer 10

• this is a tail made of 50-200 Adenine Residues

Question 11

11. What is RNA Splicing?

Answer 11

• the removal of certain fragments from the Primary
  RNA transcript

Question 12

12. What is the function of the 5’ Cap and the 3’ Poly-A
    tail?

Answer 12

1. FACILITATE
   
   • the export of the mRNA from the nucleus
2. PROTECT
   - the mRNA from degradation
   - this is caused by Hydrolytic Enzymes
3. HELP RIBOSOMES ATTACH
   
   • to the 5’ end during translation

Question 13

13. Does a large part of the genome encode for proteins?

Answer 13

• no
• it does not code for proteins
  (non-coding regions)
• it has a regulatory role
• it regulates the gene expression
• EG: Promoters

Question 14

14. What are Introns?

Answer 14

• they are non-coding regions of genes
• they have regulatory sequences
• they regulate gene expression
• they have a role in RNA splicing

Question 15

15. What are Exons?

Answer 15

• they are the coding regions of genes
• they are translated into amino acid sequences

Question 16

16. What does RNA splicing remove?

Answer 16

• it removes introns
• it adds exons and joins them together
• it creates the final mRNA molecule
• this molecules has a continuous coding sequence

Question 17

17. What carries out RNA splicing?

Answer 17

• Spliceosomes
• these are found in the nucleus of Eukaryotic cells

Question 18

18. What are Spliceosomes?

Answer 18

• they are large and complex
• they are a molecular assembly
• they consist of snRNPs
• these are small nuclear ribonucleo-proteins
• they also consist of other proteins

Question 19

19. What do the Small Ribonucleoproteins (snRNPs) consist of?

Answer 19

• they consist of proteins
• they consist of small nuclear RNA’s
• these are RNAs that have less than 250 nucleotides

Question 20

20. What do the Spliceosomes interact with?

Answer 20

• they interact with certain sites along an intron
• this intron is in the primary RNA transcript
• the spliceosome cuts the pre-mRNA
• the spliceosomes release the intron
• they join the 2 exons together

Question 21

21. Where are Spliceosomes formed?

Answer 21

• they are formed in primary mRNA molecules that
  contains introns and exons

Question 22

22. What happens within the introns?

Answer 22

• the snRNA bases pair with the nucleotides
• this happens at specific sites of the intron