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Transmission of Information
• SUMMARY
DNA
REPLICATION
DNA
TRANSCRIPTION
mRNA
TRANSLATION
amino acids
protein !
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http://www.youtube.com/watch?v=NJxobgkPEAo
http://www.youtube.com/watch?v=D5vH4Q_tAkY
http://www.youtube.com/watch?v=d1UPf7lXeO8
http://www.youtube.com/watch?v=B6O6uRb1D38
http://www.youtube.com/watch?v=yJdAxuIA6QM
http://www.youtube.com/watch?v=u9dhO0iCLww
Transcription
• Copies the DNA code to mRNA
– DNA unwinds
– Only 1 strand is transcribed
– Complimentary base pairing of nucleotides
C-G G-C T-A A-U
– This pairing forms the mRNA
– RNA polymerase helps form the new mRNA
• initiation signal - “start here”
• termination sequence - “stop synthesis”
Transcription
Termination
sequence
mRNA 5’
mRNA 3’
Translation
• Translation occurs on the
ribosomes
– Ribosome spheres dissociate into 2 parts
– Each “half” of ribosome is made of...
• rRNA
• polypetides (enzymes)
– 60S unit (larger piece of ribosome)
– 40S unit (smaller piece of ribosome)
Translation
• Translation occurs on the
ribosomes
– mRNA is “stretched out” on ribosome
– Nucleotides on the mRNA are grouped
into 3s to form: “CODONS”
• each CODON carries a 3 letter code to
translate into an amino acid
• “Anticodons” on tRNA will match-up with
the codons
Ribosome
60 S
codons
AUG
rRNA
GCU
AUG
5’
rRNA
40 S
AUG – School Starts in August
UUG
mRNA
3’
Genetic Code
• The Genetic Code
– Broken in 1961 by Marshall Nirenberg and
coworkers
– Made poly-U mRNA and “fed” it to ribosomes
– The only peptide made was phenylalanine
– Therefore, UUU codes for Phe
– Each AA is coded for by a sequence of 3
nucleotides on mRNA = CODON
Translation
• 4 STAGES in Protein Synthesis:
–Activation
–Initiation
–Elongation
–Termination
Activation
• Each AA is activated by reacting with
an ATP
• The activated AA is then attached to
particular tRNA... (with the correct anticodon)
activated AA
anticodon
fMET
C
G
A
Elongation
• The new peptide is added on and
the whole ribosome “translocates”
or moves down one codon.
• A new “A site” is available for
another AA to add.
Termination
• After the last translocation (the
last codon is a STOP), no more AA
are added.
• “Releasing factors” cleave the
last AA from the tRNA
• The polypeptide is complete