If protein cant recognize anything that it is

If protein can’t recognize anything that it is supposed to bind, it will
bind to rho factor, make it bigger and stall ribosome

o If it finds what it’s looking for, rho factor remains the same and
ribosome can transcribe
TRANSCRIPTION IN EUKARYOTES
 7-methyl guanosine caps added to 5’ end
o binds proteins and protects 5’ from degradation
 poly(A) tails added to 3’ ends
o poly(A) polymerase adds poly(A) tails, after cleavage, which are
tracts of adenosine monophosphate
o enhance stability and play role in transport from nucleus to cytoplasm
 if introns present, they are removed by RNA splicing
o snRNP complexes called “spliceosomes” remove introns and splice
exons together
 RNA polymerase
o All eukaryotic RNA polymerases require assistance of other proteins
called transcription factors in order to initiate synthesis of RNA chains
o I: catalyzes the synthesis of all ribosomal RNAs except small 5S RNA
o II: transcribes nuclear genes that encode proteins and perhaps other
genes specifying hnRNAs
o III : catazlyzes the synthesis of the transfer RNA molecules, the 5S
rRNA molecules, and small nuclear RNAs
o IV : small interfering RNAs
o V : some siRNAs plus noncoding (antisense) transcripts of siRNA target
genes
Initiation
 Initiation of transcription by RNA polymerase II requires assistance of several
transcription factors
 Promoters recognized by RNA polymerase II
o CAAT BOX : GGCCAATCT
 -80
o TATA BOX : TATAAAA
 5’  3’ and at -30
o first A 4bp after TATA: +1 position : transcription start site
o present in RNA polymerase ii PROMOTERS
 GC BOX: GGGCGG
 OCTAMER BOX: ATTTGCAT
Elongation
 Once RNA polymerases released from initiation complexes, they catalyze RNA
chain elongation same way as in prokaryotes
 5’ ends of mRNA modified by 7-methyl guanosine caps
Termination
 3’ ends produced by endonucleolytic cleavage rather than termination of
transcription

o cleavage event occurs 11-30 nucleotides downstream from an
AAUAAA sequence and upstream from a GU-rich sequence near end of
transcript
o after cleavage, poly(A) polymerase adds poly(A) tails to 3’ ends
 polyadenylation
Introns:
 not required for normal gene expression so many eukaryotic genes don’t
have
 introns are spliced out by spliceosomes
o composed of snRNPs (snRNA protein complexes) and proteins
o Five snRNAs: U1, U2, U4, U5, U6
 Introns are removed, and 2 exons on either side are joined together
o 3’ end of exon 1 joins 5’ end of exon 2
 how to tell if there is intron: if at 5’ end there is a GU and at 3’ end there is an
AG, and the intron bonding site UACUAAC (TAC BOX) is present
o everything between GU and AG is the intron and gets taken out

PROTEIN SYNTHESIS
Ribosomes form peptide bonds
o distributed through cells in prokaryotes, located in cytoplasm in
eukaryotes
o composed of one large and one small subunits which dissociate when
the translation of an mRNA molecule is completed
o E.coli:
 Small 30S subunit and large 50S subunit
o Mammalian ribosome:
 Small 18s subunit and large subunit contains 5S, 5.8S, 28S
o