From Gene to Protein - kimbiology.weebly.com · One gene-one polypeptide hypothesis •One gene-one...
Transcript of From Gene to Protein - kimbiology.weebly.com · One gene-one polypeptide hypothesis •One gene-one...
FromGenetoProteinLesson3
GregorMendel
•Mendelhypothesizedthatcertain“factors”wereresponsibleforthetraitsthatwereinheritedbypeaplants
• Today,thesefactorsareknownasgenes• AsequenceofnucleotidesinDNAthatcontaininstructionsforbuildingproteins
• Genesà Proteinsà Physicalcharacteristics,anti-bodies,hormones,proteinsthatdrivecellularmetabolism,andthosethatmanifestgeneticdisordersbytheirabsenceoralteration
ArchibaldGarrod(early1900s)
• Certainillnessesoccurredinsomefamiliesmoreoftenthanothers
• Alkaptonuriaà geneticdisorderwhereurineappearsblack
becauseitcontainsalkapton(chemical)
• InheritedtraitàMutationofagenethatnormallycodesforanenzymethat
breaksdowntheaminoacidtyrosine
• Ifnotbrokendown,chemicalcalledalkaptonaccumulates(turnsblackinair)
• Firstseethatenzymesareunderthecontrolofhereditarymaterial
Onegene-oneenzymehypothesis
• BeadleandTatum (1941)usedbreadmold
(Neurosporacrassa)
• NormalNeurosporagrowsonaminimalmedium
(MM):salts,sucroseandavitamin
• Abletousesimplechemicalstosynthesizecomplex
moleculesneededforgrowthandreproduction
• Mutantstrainsdidnotgrowunlessadditional
nutrients(i.e.aminoacidsandvitamins)wereadded
• Placedmutant
strainsinvials
containingMM
plusonemain
nutrient
• Different
mutantscould
growindifferent
conditions
• Hypothesizedthateachmutatedstrainhadadefectinagenethat
codedforoneoftheenzymesneededtomakeaparticularnutrientthat
wasnotintheMM
• Concludedthatonegene controlstheproductionofoneenzyme
• Showeddirectrelationshipbetweengenesandenzymes=onegene-
oneenzymehypothesis
Onegene-onepolypeptidehypothesis
• Onegene-oneenzymehypothesisneeded
toexpandtoincludeotherproteins
• Manyproteinsarenotenzymes,andmay
consistofmorethanonesubunit
• Subunit=polypeptide
• Restatedasonegene-onepolypeptide
hypothesis
TheCentralDogma
• FrancisCrick (1956)gavethenameCentralDogmatotheflowofinformationfrom
DNAà RNAà Protein
TheCentralDogma
Two majorsteps:
1. Transcription=informationcodedin
DNAiscopiedintoRNA(inthenucleus)
• RNAisabletoexitthenucleusandenterthe
cytosol
2. Translation =informationinRNAis
copiedintoaminoacids(onribosomes)
RibonucleicAcid(RNA)
• LikeDNA,RNAisacarrierofgeneticinformation
Deoxyribonucleic acid Ribonucleic Acid
Deoxyribose sugar Ribose sugar
Doublestranded Singlestranded
Adenine-thymineGuanine-cytosine
Adenine-uracilGuanine-cytosine
Residesinnucleus Residesinnucleusandcytoplasm
TypesofRNA
• MessengerRNA(mRNA) =endproductoftranscriptionofagene
• Variesinlengthdependingonthesizeofthegene
• Translatedbyribosomesintoprotein
• TransferRNA(tRNA) =deliversaminoacidstotheribosomesfortranslation
• Shortinlength(70-90bplong)
• RibosomalRNA(rRNA)=bindswithribosomalproteintoformribosomes
• MessengerRNA(mRNA) =
endproductoftranscription
• TransferRNA(tRNA) =
deliversaminoacidsfor
translation
• RibosomalRNA(rRNA)=
bindswithribosomalprotein
toformribosomes
TranscriptionandTranslation:Overview
Transcription(3sequentialprocesses):
1. Initiation– enzymeRNApolymerasebindstoDNAataspecificsite
2. Elongation- RNApolymerasereadsthetemplatestrandofDNAandcreatesa
complementarystrandofRNA
3. Termination– recognizescodetostopàmRNAtranscriptreleasedfromnucleus
TranscriptionandTranslation:Overview
Translation(3sequentialprocesses):
1. Initiation– ribosomerecognizesaspecificsequenceonthemRNAandbindstothesite
2. Elongation– ribosomemovesalongthemRNA3nucleotidesatatime(each3nucleotides=anaminoacid)
3. Termination– a3-basesequenceisreachedthatcodesfora“stop”signalà ribosomefallsoffmRNAandpolypeptidechainisreleased
TheGeneticCode
• Universal – virusestobacteriatomammals
(exceptions)
• 4basesinRNAà 20aminoacids(AA)foundinproteins
• Sequenceof3nucleotides(codon)usedforeachAA
• Startcodon- signalinginitiationfortranslation• AUG(Met)
• Stopcodon - signalingterminationattheendof
translation
• UAA,UAG,UGA
Homework
• Investigation6.4.1
•WorkingroupstocreatearoleplayforDNAreplication
(role-playandquestionsdueFridayNov17)
• TextbookQuestions