Transcription and Splicing

Question 2

Describe how mRNA is produced from an exposed template strand of DNA (do not include DNA helicase or splicing in your answer)

Answer 2

• Free RNA nucleotides form complementary base pairs;
• Phosphodiester bonds form;
• By (action of) RNA polymerase;

Question 3

How is the structure of pre-mRNA different to mRNA?

Answer 3

• mRNA fewer nucleotides/pre-mRNA has introns and exons
• because of splicing

Question 4

What is the first step of transcription?

Answer 4

(DNA helicase) causes hydrogen bonds between complementary base pairs to break in a specific region of DNA causing the strand to separate and expose the nucleotide bases

Question 5

After they have separated, what does the single-strand of DNA act as?

Answer 5

template strand

Question 6

What is the role of RNA polymerase?

Answer 6

to catalyse the reaction forming phosphodiester bonds between adjacent nucleotides, helping to form a pre-mRNA molecule

Question 7

Describe how mRNA is formed by transcription in eukaryotes (7 marking points)

Answer 7

• Hydrogen bonds (between DNA bases) break
• one DNA strand acts as a template
• RNA nucleotides align by complementary base pairing
• Uracil base pairs with adenine
• RNA polymerase joins (adjacent RNA) nucleotides
• (By) phosphodiester bonds
• Pre-mRNA is spliced (to form mRNA)

Question 8

How does transcription differ in prokaryotes compared to eukaryotes?

Answer 8

In prokaryotes, transcription results directly in the production of mRNA, as prokaryotic DNA does not have introns

Question 9

What is splicing?

Answer 9

the process which removes intons from a strand of pre-mRNA

Question 10

How do mRNA molecules leave the nucleus?

Answer 10

through a nuclear pore (they are too large to diffuse out)

Question 11

Where does transcription occur?

Answer 11

• in the nucleus in eukaryotic cells
• in the cytoplasm for prokaryotic cells