7.3 Transcription Flashcards
1
Q
State the direction in which transcription occurs
A
Transcription occur in a 5’-3’ direction
2
Q
Outline the features of the antisense strand
A
- Transcribed into RNA
- Carries the complementary version of the genetic code
- Its sequence will be complementary to the RNA sequence and will be the “DNA version” of the tRNA anticodon sequence
3
Q
Outline the features of the sense strand
A
- Not transcribed into RNA
- Contains the genetic code
- Its sequence will be the “DNA version” of the RNA sequence (identical except for T instead of U)
4
Q
Explain the process of transcription in prokaryotes
A
- Transcription begins at a promoter region: a short series of bases which are not transcribed, but allow RNA polymerase to attach and determine which is the antisense strand.
- RNA polymerase adds nucleoside triphosphates complementary to the antisense strand to create a chain in the 5’-3’ direction, forming phosphodiester bonds between the nucleosides. As triphosphates are added, 2 phosphates are released creating RNA nucleotides, which form the mRNA strand.
- Transcription is stopped by a terminator sequence, a sequence of bases on the antisense DNA strand that when transcribed cause RNA polymerase to detach from DNA, ending the transcription process.
5
Q
Outline why and how mature mRNA is formed
A
Sections of the mRNA strand called introns (interrupting sequences) carry a base sequence not required for translation. These introns are spliced out, leaving only exons (expressed sequences). Exons are joined to form a mature mRNA strand, carrying the mRNA version of the gene’s base sequence.