25. RNA STRUCTURE AND FUNCTION

Question 1

1. What is RNA?

Answer 1

• Ribonucleic acid
• it is produced by the transcription of DNA
• it is a single stranded molecule
• it consists of ribonucleotides

Question 2

2. What do Ribonucleotides consist of?

Answer 2

1. A nitrogenous base
   - (U, A, G, C)
   - Uracil replaces Thymine
2. A pentose sugar
   (Ribose)
3. A phosphate Group

Question 3

3. What are 5 differences between DNA and RNA?

Answer 3

1. DNA is double stranded
   - RNA is single stranded
2. The sugar in DNA is deoxyribose
   
   • the sugar in RNA is ribose
3. The Nitrogenous bases in DNA: T, A, C, G
   - the Nitrogenous bases in RNA: U, A, C, G
4. DNA is composed on deoxyribose nucleotides
   - RNA is composed of ribose nucleotides
5. DNA is found in the nucleus
   - RNA is found in the cytoplasm

Question 4

4. What are the 3 main types of RNA?

Answer 4

1. mRNA
   - this is the messenger RNA
   - it is translated into proteins
2. rRNA
   - this is Ribosomal RNA
   - it forms part of the ribosome structure
3. tRNA:
   - this is transfer RNA
   - it transfers the Amino acids to the growing
   polypeptide chain
   - this happens during translation

Question 5

5. What is Transcription?

Answer 5

• this is the synthesis of proteins
• it is a directed by DNA
• it is the first stage of gene expression

Question 6

6. What is Transcription catalysed by?

Answer 6

• RNA Polymerase

Question 7

7. What is Transcription similar to?

Answer 7

• it is similar to DNA replication
• except Uracil replaces Thymine

Question 8

8. What does Transcription start with?

Answer 8

• it starts with the binding of the RNA Polymerase
• to a promoter

Question 9

9. What is a Promoter?

Answer 9

• this is a part of the DNA sequence
• the RNA Polymerase attaches to it
• it is located at the 5’ end of the gene

Question 10

10. What is the 5’ end of the gene known as?

Answer 10

• Upstream

Question 11

11. What is the Terminator?

Answer 11

• this is a sequence
• it signals the end of Transcription in Bacteria
• this is different for Eukaryotes

Question 12

12. What is the unit of Transcription?

Answer 12

• this is the stretch of the DNA that is transcribed

Question 13

13. How many RNA polymerases do Bacteria have?

Answer 13

• Bacteria only have one RNA Polymerase

Question 14

14. How many RNA Polymerases do Eukaryotes have?

Answer 14

• 3 types of RNA Polymerases

THE RNA POLYMERASE INVOLVED IN TRANSCRIPTION:
- is RNA Polymerase II

Question 15

15. What does RNA Polymerase do?

Answer 15

• it synthesises RNA
• it does this using the DNA template strand
• it only transcribes 1 of the 2 DNA strands
• it transcribes the 3’ - 5’ strand

THE RNA POLYMERASE:
- adds nucleotide triphosphates (NTPs) only in the 5’ - 3’
direction
- it does not require the presence of a primer to do so

Question 16

16. What does Eukaryotic RNA Polymerase I do?

Answer 16

• it is responsible for the rRNA synthesis
• 5.8S
• 60 S Ribosomal subunits

Question 17

17. What does Eukaryotic RNA Polymerase II do?

Answer 17

• it is responsible for the synthesis of mRNA
• and the synthesis of snRNAs

Question 18

18. What does Eukaryotic RNA Polymerase III do?

Answer 18

• it is responsible for the synthesis of tRNA
• and the synthesis of small RNAs
• like 5S (60S) rRNA subunits

Question 19

19. What are the three stages of Transcription?

Answer 19

1. Initiation
2. Elongation
3. Termination

Question 20

20. Provide a definition for Initiation?

Answer 20

• the RNA Polymerase II binds to the promoter

Question 21

21. Provide a definition for Elongation?

Answer 21

• the RNA polymerase adds Nucleotide Triphosphates
  to the strand in the 5’-3’ direction

MRNA IS PRODUCED:
- in the 5’-3’ direction always

DNA TEMPLATE:
- is read in the 3’ -5’ direction always

Question 22

22. Provide a definition for Termination?

Answer 22

• the RNA transcript is released from the DNA
• this happens when it reaches the termination of
  transcription

Question 23

23. Provide a label for number 1.

Answer 23

• the RNA Polymerase II will bind to the promoter
• the DNA strands will unwind
• the RNA Polymerase II will initiate RNA synthesis
• this is Initiation

Question 24

24. Provide a label for Number 2.

Answer 24

• the RNA Polymerase II moves downstream
• it unwinds the DNA
• it elongates the RNA strand in a 5’-3’ direction
• it does this by adding Nucleotide Triphosphates
• this is Elongation

Question 25

25. Provide a label for Number 3.

Answer 25

- the RNA transcript (strand) is released - the RNA Polymerase II detaches from the DNA - this is Termination

Question 26

26. Name the 4 factors that aid in the Initiation of Transcription in Eukaryotes?

Answer 26

1. Promoters 2. General Transcription Factors 3. Transcription Initiation Complex 4. TATA Box

Question 27

27. What are Promoters?

Answer 27

- they signal the initiation of RNA synthesis - they do this by binding to the RNA Polymerase II

Question 28

28. What are General Transcription factors?

Answer 28

- these are proteins - they mediate the binding of RNA Polymerase II to the promoter - several of these must bind to the Promoter before the RNA Polymerase II can - they mediate the initiation of Transcription

Question 29

29. What are Transcription Initiation Complexes?

Answer 29

- they are the transcription factors and the RNA Polymerase II - they are bound to a promoter

Question 30

30. What is the TATA Box?

Answer 30

- this is a specific sequence within a promoter - it is responsible for the assembly of the transcription initiation complex - in eukaryotes

Question 31

31. What are the 2 stages of Transcription Initiation?

Answer 31

1. THE GENERAL TRANSCRIPTION FACTORS - bind to the TATA box - this happens within the Promoter 2. THE RNA POLYMERASE II IS RECRUITED - it binds to the promoter