Transcription Flashcards
where does transcription take place in eukaryotes?
in the nucleus
what does transcription produce?
pre- mRNA
how many amino acids are there?
20
how many RNA polymerases do eukaryotes have? and which is used for mRNA synthesis?
3 in their nuclei and polymerase ll is used
what are the 3 stages of transcription?
1) initiation
2) elongation
3) termination
what happens in the initiation stage?
RNA polymerase binds to the promotor and initiates synthesis and the DNA strands unwind
what is different about the initiation stage in eukaryotes in comparison to prokaryotes?
transcription factors mediate the binding of RNA polymerase by binding to the TATA box
what happens in the elongation stage?
polymerases move downstream unwinding the DNA and RNA polymerase transcribes the DNA
what happens in the termination stage?
RNA transcript is released and polymerase detaches
what signals termination in eukaryotes?
polyadenylation sequences - UTRS
what happens during modification of pre-mRNA in eukaryote?
5 prime end receives a 5 prime cap and 3 prime end receives a poly a tail
what 3 things do the modifications facilitate?
- export into the cytoplasm
- protection from hydrolytic enzymes
- help ribosomes attach to 5 prime end
what is the function of the UTRs?
ribosome building - not translated into proteins
what are non coding regions called?
introns
what happens to introns?
they are spliced out by spliceosomes
how does the spliceosome know where to cut intron?
they have base pairs which complementary to specific nucleotides on the introns
what is alternative RNA splicing?
different introns are spliced out producing different exons coding for different proteins
what is the advantage of alternative RNA splicing?
the number of proteins an organism can produce is much greater than the number of genes
what does it mean that the genetic code is degenerate?
amino acids can be coded for by more than one codon
what is unique in protein coding in prokaryotes?
coupling of transcription and translation and the DNA is not segregated from the ribosomes
