proteinsyntheis-090507044219-phpapp01 (2)

8/7/2019 proteinsyntheis-090507044219-phpapp01 (2)

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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.

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