Lecture 18- Transcription in Eukaryotes Flashcards
What are the three polymerases used for transcription in eukaryotes and what are each of their uses?
RNA polymerase I: used to transcribe rRNA.
RNA polymerase II: used to transcribe mRNA.
RNA polymerase III: used to transcribe tRNA.
What is the promoter region for RNA polymerase II?
It is called the TATA box.
What else is required for the initiation of eukaryotic transcription?
Transcription factors. These are proteins that bind to DNA and allow RNA polymerase II to bind to the promoter.
What is the initiation complex?
The interaction between the promoter, the transcription factors, and RNA polymerase II.
What must happen to the mRNA before it exits the nucleus?
The mRNA must be modified into mature mRNA. This transformed mRNA will have a 5’ mehtyl-G cap and a 3’ poly-A tail containing 100-200 As.
What allows eukaryotes to function with so few genes?
mRNA editing, or splicing, which allows one gene to code for many different proteins.
What are introns and exons?
Introns are sequences of pre mRNA that are cut out and remain in the nucleus.
Exons are the sections of pre mRNA that remain in the mature mRNA, these are the regions that actually code, and exit the nucleus.
How do exons determine the mature mRNA sequence?
Genes contain many exons, which do not all make it to the mature mRNA. Depending on which exons make it, the protein will be different.
How does splicing happen and what carries it out?
Splicing is carried out by the spliceosome, which is made of snRNPs (small nuclear ribonucloeprotein particles) that contain RNA that matches to the specific sequence at the start and end of the intron (same sequence). The snRNPs will cleave out the introns and the exons will then be joined.
How does the cell read the message found in mRNA? What is the start sequence?
The ribosome reads triplets of nucleotides, or codons. The start codon is AUG, which codes for methymine.
