Transcription Flashcards
What is transcription?
process of copying a gene’s DNA sequence into mRNA
What are the 3 steps of transcription?
- Initiation
- Elongation
- Termination
What is initiation?
Process where RNA polymerase binds to the promoter region of DNA and begins RNA synthesis
Where does transcription begin?
Begins at a promoter which is a sequence of DNA
What are transcriptional factors?
They mediate the binding of RNA polymerase and the initiation of transcription
What is the transcription initiation complex?
The completed assembly of transcription factors and RNA polymerase II bound to a promoter
Where does transcription begin in eukaryotes?
At the TATA box
What is elongation?
RNA polymerase moves along the DNA, synthesizing the RNA strand by adding complementary RNA nucleotides
What is a transcription bubble?
the unwound section of DNA during elongation, exposing 10-20 bases at a time for RNA synthesis
In which direction does RNA polymerase synthesize mRNA?
mRNA is synthesized in the 5’ to 3’ direction
What is termination?
RNA polymerase releases the RNA strand and detaches from the DNA after reaching a stop codon
Termination - Prokaryotes
- RNA polymerase stops transcription at stop codon
- mRNA can be translated without further modification
Termination - Eukaryotes
- RNA polymerase II transcribes a polyadenylation signal sequence
- RNA transcript is released 10-35 nucleotides past this sequence
What is a polyadneylation signal?
- It signals the termination of transcription and addition of a poly-A tail to the mRNA
- AAUAAA
What are ribozymes
Catalytic RNA molecules that function as enzymes
Why are introns important?
They can contain sequences that might regulate gene expression or include promoter elements
What is alternative RNA splicing?
It allows genes to encode multiple polypeptides by varying which segments are treated as exons during splicing
What are protein domains?
molecular architecture consisting of discrete regions in proteins
What do individual exons code for in a protein?
They code for different domains in a protein
What is exon shuffling?
The rearrangement of exons, potentially leading to the evolution of new proteins
3 parts of mRNA processing
- 5’ Cap is placed on the 5’ end of mRNA
- Poly-A Tail is placed on 3’ end of mRNA
- Introns are spliced out
5’ Cap Functions
Provides protection to the 5’ end
Poly-A Tail Functions
Protects 3’ end from degradations and helps ribosomal attachment
