Transcription Flashcards
What need to happen for a protein to be made?
A copy of the genetic code has to be taken from the nucleus to the cytoplasm.
Since DNA can’t leave the nucleus, what needs to happen?
The code (message) has to be carried by another molecule- mRNA
What is transcription?
The process of synthesising mRNA from a section of DNA.
Where does transcript happen?
In the nucleus
What does DNA in the nucleus act as?
A template for the production of a single strand of mRNA.
What are the stages of transcription?
- Enzyme RNA polymerase unwinds a length of DNA.
- The weak hydrogen bonds between the bases break.
- Free RNA nucleotides line up against their complementary base partner of the exposed DNA bases on the template strand. ( A-U, C-G)
- RNA polymerase adds nucleotides to the 3’ end of the mRNA molecule until a stop sequence is reached.
- mRNA peels away from the DNA template. Double helix recoils.
- A primary mRNA transcript has now been formed.
Describe RNA splicing
Normally a section of DNA that is transcribed is around 8000 nucleotides long yet only around 1200 nucleotides code for a polypeptide.
What are the non-coding regions called?
Introns
What are the coding regions called?
Exons
Describe where introns normally are?
Introns are normally interspersed between the coding regions (exons)
What does a primary mRNA transcript contain?
Both exons and introns
Since introns are not required for the formation of a polypeptide chain, what happens to them?
They are removed from the primary transcript.
If introns are removed from the primary transcript, what happens to the remaining exons?
The remaining exons are then spliced together to form the mature mRNA transcript.
What does the mature mRNA transcript do after it is formed?
It then leaves the nucleus and enters the cytoplasm where it becomes attached to a ribosome.
What happens during transcription to the RNA base sequence?
The RNA base sequence is a ‘mirror’ image of the DNA base sequence.
