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Title: Transcription Translation.
Description: University notes on Transcription Translation.
Description: University notes on Transcription Translation.
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Transcription and Translation
Transcription
• Copying the information encoded in the
chemical DNA into a closely related
chemical, RNA, i
...
transcribing it
...
coli promoters
-35
17 bp
-10
TTGACA
TATAAT
Pribnow
+1
Start
A/G
Search for promoter
Closed-promoter
complex
Open-promoter
complex
Unwinds DNA –10 to –1
Binds Mg2+
DNA unwound –12 to +2
Transcription
Bubble
RNA poly has b
...
for 2 rNTP
1
...
Binds any rNTP
s released,
RNA poly
continues
Initiation complete
Elongation
Unwinding
Coding strand
Rewinding
Direction of transcription
50 nucleotides per sec, 170 Ǻ
Transcription bubble moves
RNA polymerase unwinds and rewinds DNA
Nascent RNA strand diverts out of polymerase just ahead
of the rewinding of DNA
• Unlike DNA synthesis there is no editing during synthesis,
RNA poly has no nuclease activity
• Greater number of errors 1 in 104 105 , but not as likely to
be harmful
•
•
•
•
Termination
Factor independent termination
•Signal encoded in sequence
•Palindromic GC rich sequence
•Stretch of A’s
• Harder to unwind GC rich DNA so RNA poly pauses
• Palindromic sequences form Hairpin structure, which weakens
interaction of RNA polymerase with DNA strand
• RNA poly moves on to the run of A residues, incorporates U’s
...
e
...
Translation
1
...
2
...
3
...
Protein synthesis catalyzed by ribosomes
...
The genetic code
1
...
2
...
Many
synonyms have similar nucleotides in
the first two positions and differ only
in their third position
...
UAG, UAA, and UGA are Stop
codons
...
4
...
Signals the start point for synthesis
...
The code is not universal
...
Overview of RNA molecules involved in Translation:
mRNA, tRNA, and rRNA
rRNA
Part of ribosome
mRNA
Carries message
tRNA
Transfers amino acids
mRNA
1
...
3
...
coli lac operon
Message for a single protein contained in a single open reading frame (orf) lac x,
y, z genes
...
Shine-Dalgarno sequence (SD in figure)
Upstream from start codon, helps ribosome find correct start site
Complementary to 3’ end of 16S rRNA
Structure of tRNAs
•Single strand of RNA, 73-93 residues
•Many unusual bases
•High degree of base pairing
•CCA at 3’ end (3’OH for aa attachment)
More accurate 3D version
Cloverleaf diagram
3’ 7 bp acceptor stem
Anticodon loop
Aminoacyl-tRNA
synthetase (enzyme)
Amino acid
P P P
Charging a tRNA
Adenosine
ATP
P
P Pi
Pi
Adenosine
tRNA
Aminoacyl-tRNA
synthetase
Pi
tRNA
P
Adenosine
AMP
Computer model
Aminoacyl-tRNA
(“charged tRNA”)
rRNA in ribosomes
• Ribosome is a complex of proteins and rRNA
• Two major subunits
Schematic of ribosome
Initiation
Dissociation of 70S
Promoted by IF1 and assisted by IF3
fMet-tRNAfMet
30S initiation complex
Binds mRNA, fMet-tRNAfMet
70S initiation complex
•50S subunit binds
Shine-Dalgarno
sequence can base pairs
with 3’ end of the 16S
rRNA
fMet-tRNAf Met bound
in the P-site of ribosome
Elongation
A cyclical process
Transpeptidation
Translocation
Termination
Protein release factors
Uncharged tRNA and
peptide released from
ribosome, which is
accompanied by GTP
hydrolysis and RFs
released
Title: Transcription Translation.
Description: University notes on Transcription Translation.
Description: University notes on Transcription Translation.