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TRANSLATION
The molecular basis of protein
synthesis
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Miniature machinery
• We are now going to look at the molecular
basis for protein synthesis
• Just like in DNA synthesis, there are specific
proteins and molecules that are responsible
for carrying out the process of transcription
and translation
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Transcription
• Remember that the first step in protein
synthesis is copying the DNA into mRNA
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How does it know where to start?
• Specific genes encoded in DNA have a
sequence at the start known as a PROMOTER
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A brief overview
• http://www.johnkyrk.com/DNAtranscription.h
tml
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New mRNA
• Newly synthesized mRNA can then undergo
modifications
• These modifications include:
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Controlling the copies
• mRNA is not as stable a molecule as DNA – it has
tendency to break down really easily
• mRNAases – enzymes that break mRNA down help to
accelerate this process to control protein production
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Post-transcriptional modifications
• To help control mRNA survival, a few
modifications are made:
• 5’ cap: made up of methyl guanosine that
protects against enzymes that break down
mRNA
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Removal of Introns
• Modification of mRNA after transcription may be necessary to
remove redundant information found in DNA
• Remember that DNA often contains excess information that is
not necessary - these parts are called introns
• http://highered.mcgrawhill.com/sites/9834092339/student_view0/chapter16/animati
on_-_exon_shuffling.html
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Translation
• Once copied, mRNA leaves the nucleus
through the nuclear pores in the nuclear
membrane and moves into the cytoplasm
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Corral and tie
• Essentially, the ribosome is responsible for
reading the mRNA and polymerizing (sticking
together) the amino acids together to form the
new protein
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tRNA
• Since tRNA is essentially
RNA it contains the
same base pairs and are
used as the basis of
translation
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Ribosome structure: an overview
• And a smaller “bottom” bun known as the 30S
subunit
• Multiple RNA can read one mRNA copy at
once, creating bulk amounts of a given protein
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E, P, A
• The large 50S subunit has 3 active sites lodged into it
known as the E, P, and A site
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All together now
• Ribosome sandwiches the mRNA
• tRNA with appropriate anti-codon attaches to the
exposed codon in the A-site
• Ribosome polymerizes the amino acid attached to the
tRNA in the P-site to the new polypeptide chain
• http://en.wikipedia.org/wiki/File:Translation.gif
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Starting and ending
• Special codons located at the beginning and
end of an mRNA sequence help to indicate
where the ribosome should attach and where
it should separate
• A start codon initiates the polypeptide
sequence; it usually codes for the amino acid
methionine
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Energy needed!
• Notice that this process requires energy – the
hydrolysis of GTP (a molecule similar to ATP)
provides the ribosome energy
• GTP is needed to:
– Polymerize the incoming amino acid to the
polypeptide chain
– Translocate (move) the tRNA to the next bonding
site
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Chance meeting
• Remember that with numerous tRNA floating around
a small cell, there is no mechanism that brings tRNAs
to the ribosome
• Nice to know the production of necessary
components of your body is dependent on random
movement!
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• http://www.biostudio.com/demo_freeman_pr
otein_synthesis.htm
• Check this out at home:
• http://www.learnerstv.com/animation/animat
ion.php?ani=181&cat=biology
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