Transcription and mRNA processing Flashcards
RNA polymerase
catalyzes RNA synthesis, pries DNA strands apart and joins together RNA nucleotides
Anatomy of Gene: bacteria
Upstream sequence: transcription initiation sequence and promoter
Downstream sequence: transcription termination site and terminator
Three stages of transcription
Initiation, elongation, termination
Initiation
After RNA polymerase binds to promoter, the polymerase unwinds the DNA strands and begins RNA synthesist start point of template strand
Elongation
the polymerase moves downstream, unwinding the DNA and elongating the RNA transcript in a 5’ to 3’ direction; after transcription, DNA strands rejoin and form double helix
Termination
RNA transcript is released and polymerase detaches from DNA
Promoter
specific nucleotide sequence in DNA of a gene that binds RNA polymerase; positioned to start transcribing RNA at appropriate place
Terminator
In bacteria; sequence of nucleotides in DNA that marks ends of genes and signals RNA polymerase to release newly synthesized RNA and detach from DNA
Transcription unit
Region of DNA that is transcribed into RNA molecule
Anatomy of a Gene: Eukaryotes
Upstream: Transcription initiation site and promoter
5’ UTR
Downstream: 3’ UTR; AAUAAA (polyadenylation signal) and transcription termination site
RNA processing (eukaryotic)
Modification of RNA primary transcripts including splicing of introns, joining axons, and alteration of 5’ and/or 3’ ends
Alteration of mRNA ends
5’ end: modified 5’ cap
3’ end: poly-A tail
Why are mRNA ends changed?
to facilitate mRNA export to cytoplasm, protect mRNA from hydrolytic enzymes, help ribosomes attach to 5’ end
5’ cap
modified guanine nucleotide attaches to 5’ end
Poly-A tail
50-250 adenine nucleotides attached to 3’ end
RNA splicing
removal of portions of the primary transcript (introns) that will not be included in mRNA; joining together of remaining portions (Exons)
Introns
noncoding, intervening sequence within a primary transcript that is removed during RNA processing
Exons
sequence within primary transcript that remains in RNA after processing
Spliceosome
large complex made of protein and RNA molecules that splices RNA by interacting with ends of RNA introns; releases intron and joins together two exons
Ribozymes
Catalytic RNA molecules that function as enzymes; example is intron catalyzing its own removal
Alternative RNA splicing
eukaryotic gene regulation at RNA processing level; different mRNA molecules are produced from same primary transcript, depending on introns and exons
