Transcription

Question 1

Describe what happens in transcription

Answer 1

• Hydrogen bonds between complementary bases break, causing the strands of DNA to separate
• Free RNA nucleotides line up opposite their complementary pairs and hydrogen bonds form between them
• RNA polymerase catalyses the formation of phosphodiester bonds to join the RNA nucleotides together
• After splicing, where the introns are removed, the mRNA leaves the nucleus through nuclear pores

Question 2

What is the difference in transcription between eukaryotes and prokaryotes?

Answer 2

Prokaryote DNA does not contain introns, so there is no splicing.

Question 3

What is splicing?

Answer 3

Splicing is where the introns (non-coding regions) are removed from the pre-mRNA before the exons are reattached.

Question 4

What is pre-mRNA?

Answer 4

Pre-mRNA is the mRNA produced during transcription in eukaryotes. It contains both introns and exons.

Question 5

In a eukaryotic cell, transcription results in a molecule of pre-mRNA that is modified to produce mRNA. In a prokaryotic cell transcription produces mRNA directly. Explain this difference.

Answer 5

1. DNA of eukaryotic cell has non-coding regions / introns within gene Allow converse: (But) a prokaryotic cell does not have non-coding regions / introns in DNA; OR pre-mRNA contains non-coding regions / introns;
2. (After transcription / during modification) these regions are removed from (pre-)mRNA