7.2 Transcription Flashcards
Transcription divided into?
initiation, elongation, termination
Initiation
begins when RNA polymerase binds to DNA and unwinds near beginning of gene
promoter
nucleotide sequence lies before gene and allows binding of RNA polymerase
TATA box
region of promoter that enables binding of RNA polymerase
- has high percent of adenine and thymine bases
transcription unit
part of gene transcribed into RNA
Elongation
starts building ss RNA molecule after RNA polymerase binds to promoter and opens DNA double helix
- as RNA polymerase moves alone DNA, unwinds DNA at forward end of enzyme
- RNA molecule temporaitly winds to template; growing DNA strands unwind from DNA and extend from RNA polymerase as single nucleotide chain
- as RNA polymerase passes, DNA double helix forms
coding strand
DNA strand not being copied but contains same sequence as new RNA molecule
termination
prokaryotes 2 mechanisms:
1. protein binding to mRNA
2. mRNA binds to self and in hairpin loop, stopping transcription
- eukaryotes string of adenines transcribed as uracils on RNA
- nuclear protein binds to polyuracil site and stops transcription, newly synthesized RNA dissociates from DNA template strand
post-transcriptional modifications
pre-mRNA vulnerable to enzymes that undergo additional modification before reach nucleus and reach ribosomes
- modification is addition of nucleotides to 3’ end of pre-mRNA molecule
- also beginning of pre-mRNA transcript 5’ cap added by diff enzyme
poly (A) tail
chain of adenine added to 3’ end of pre-mRNA
5’ cap
sequence of 7 g’s added to start of pre-mRNA; ribosomes recognize site and use it as site of initial attachment
exon
sequence of DNA or RNA that codes for part of gene
intron
non coding sequence of DNA
spliceosome
enzyme protein complex that removes introns from mRNA
small ribonucleoprotein
protein binds to introns and signals them for removal
