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