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PROTEIN SYNTHESIS The formation of new proteins
using the code carried on DNA
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Gene is Selected
A gene is a sectionofDNA codingfor
a particularpolypeptideorprotein.
When a proteinisrequired bythecellortheorganism as a whole,thegene
forthat proteinis activated.
Gene
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Introns and Exons
DNA ismadeup ofcodingsequencescalledexons andnoncoding
sequencescalledintrons.
Exon Exon Exon Exon
Intron Intron Intron Intron
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Transcription
AnenzymeRNA Polymerase
unwindsthesectionofDNA carrying
thedesiredgene.
Onlyonestrandofthe DNA (the
template)isrecognised.
RNA Polymerasethen bindsto a
promotersite and beginstoform anRNA copyofthetemplatestrand
(calledmessengerRNA (mRNA)).
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Naming the Strands
AnmRNA copyofthetop coding
strand ismade by base pairing with
the bottomtemplatestrand.
DNA
Primary RNA
Codingstrand
Templatestrand
The DNA strandisunwoundexposing
the basesthatcarrythegeneticcode.
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Messenger RNA
Freenucleotidesmatch up with the
codedsequenceofDNA.
When bases pair,U
rac
il is presentinRNA insteadofThymine.
A singlestrandedprimary transcript
thatiscomplementarytothetemplate
strandisformed. DNA template TAC GCC AAATCC
mRNA codons AUG CGG UUU AGG
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Removal of Introns
The primarytranscriptcontains a
copyofboth introns andexons.
Introns areremoved andexons are
spliced (joined)toformmaturemRNA.
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Movement of mRNA
ThecompletedsinglestrandofmRNA
migratesoutofthenucleusthrough
poresinthenuclearmembrane.
mRNA bindstoribosomes.
ThemRNA isdividedintotripletsof
basescalledcodons.
Differentcodonscarrythecodeforaparticularamino acid (AA)
Othercodonscarrystart andstop
codes.
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Important Codon Facts
AUGisthestart codonon allviable
mRNAmolecules.It alsocodesfor
the amino acid Methionine.
UAA, UAG, UGA arestop codes.
Manycodons aredegenerate --more
thanonecodoncodesforan AA.
Thecodeisuniversal.Thesamecodes workin allorganisms.
43 differentcombinationsgive 64
differentcodons.
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Amino Acid Codons
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Transfer RNA
U A C
AAMethionine
TransferRNA (tRNA)is a carrier
molecule which picksup amino acids
fromthecytoplasm andcarriesthem
tothemRNA / ribosomecomplex.
anticodon
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Translation
A tripletofbasesonthetRNA called
ananticodon matches with the
mRNA codon.
tRNA carryingits AA bindstothe
codon
Theribosomemoves alongthe
mRNA activatingnew codons. AAs are joined bypeptide bonds to
formlong polypeptidechains.
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Ribosome Action
A U G C G G U U U A G G C C C U A G
Theribosome acts ascatalyst holding
allthecomponentstogetherwhile
bonds are formed.
G C C
AA2
U A C
AA1
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Peptide Bond Formation
A U G C G G U U U A G G C C C U A G
Astheribosomemoves alongthe
mRNA, amino acids are addeduntil a
stop signalisreached.
A U C
stopAA1
AA4AA3AA2 AA5
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Translation speed
Rapid proteinformationcan be
achieved whenthemRNA is
attachedtomorethanoneribosome.
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ElectronMicroscope View
mRNA (purple) bindsto a ribosome.
BeadsofAAs (yellow) are joinedto
form a polypeptide.
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Questions Whatnameisgivento a sectionofDNA codingfora
polypeptide?
Gene.
ThecodingsequencesofDNA areknown as what?
Exons.
Nametheenzymeresponsibleforunwindingthe DNA
helix.
RNA Polymerase.
How doestheenzymerecognizethestartofa
message?
It bindsto a promotersite.
Which DNA strandisusedinthe base pairing process?
Thetemplate.
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Whatnameisgiventothe RNA strandfirstformed,thatcontainsintrons andexons?
Primarytranscript.
In RNA, which base binds with Adenine?
Uracil.
WhatisthecodonforthestartofanmRNA?
AUG.
What arethethreestop codons?
UAA, UAG, UGA.
Whatdoestheterm codons aredegeneratemean?
Morethanonecodonmaycodeforan amino acid.
Whyisthecodon a three basesequence? 43 differentcombinationsgivescodesforall 20
amino acids,start andstop codes plusdegeneratecodes.
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Whatdoestheterm, thegeneticcodeisuniversal
mean?
Thesamecode worksin allorganisms.
Whatnameisgiventothe processofformingmRNA?
Transcription.
WhatisthefullnamefortRNA?
TransferRibonucleic acid. WhatistheroleoftRNA?
Carries amino acidsfromthecytoplasmtothe
ribosomes.
mRNA has a codon,tRNA has an? Anticodon.
What holds amino acidstogetherin a polypeptide?
Peptide bonds.
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Whatistheroleoftheribosomes?
They act ascatalysts, holdingthevarious
componentstogether.
How dotheribosomesoperatethat allowslong
amino acidchainstoform?
Theymove alongthemRNA allowingtRNAsto bring
innew amino acids. Whatnameisgiventothe processofconverting an
mRNA codeinto an amino acidsequence?
Translation.
Describeone wayin which therateoftranslationcanbeincreased?
By attachingthemRNA tomorethanoneribosome.