3.7 - Transcription Flashcards
What are the 3 stages of transcription?
- Initiation
- Elongation
- Termination
During transcription…
What is the initiation stage?
Genetics: transcription
- a promotor region on the DNA tells RNA polymerase where it should start binding
- the DNA strand begins to unwind & open to prepare for it to be copied
During transcription…
What is the elongation stage?
Genetics: transcription
- RNA polymerase begins to move along the DNA strand, creating a copy RNA strand. (in the 5’ to 3’ direction)
- DNA that is already copied or no longer needed is reformed into a double helix
During transcription…
What is the termination stage?
Genetics: transcription
- a terminating sequence indicates the end of a gene
- both RNA polymerase and the new RNA strand seperate from the DNA and continue on
What are the 3 post-transcription modifications of an RNA strand?
Describe them.
5’ cap:
- added to the 5’ end
- made of modified guanine triphosphate
- protects mRNA from nucleases in cytoplasm
poly-A tail:
- added to 3’ prime end
- made of adenine nucleotides in a row
- used for protection
- tail put in place by enzyme called poly-A tail polymerase
Exons:
- areas on the mRNA to make proteins
- Introns (areas not used for making proteins) are removed by molecules called spliceosomers so only exons are left
What must mRNA do before it leaves the nucleus?
It must go through post-transcription modifications
What are exons?
genetics
regions on mRNA that are used to make proteins
( these sequences are expressed)
What are introns?
regions on mRNA that do not make proteins
(interupting sequences)
What is alternative splicing?
Genetics
- a single gene can produce pre-mRNA that can be spliced in multiple ways
- Meaning… a single gene can create man different mature mRNA from the same family, which can later create a variety of different proteins
- one gene = multiple proteins
- goes against one gene to one protein theory
