Nucleic Acids & Protein Synthesis DNA Structure & Function Replication RNA Structure & Function ...

Nucleic Acids Nucleic Acids & Protein Synthesis& Protein Synthesis

DNA Structure & FunctionDNA Structure & FunctionReplicationReplication

RNA Structure & FunctionRNA Structure & FunctionTranscriptionTranscription

Protein SynthesisProtein SynthesisTranslationTranslation

DNADNA

• The Search for the Double Helix The Search for the Double Helix • Structure of DNAStructure of DNA

– ComponentsComponents– The Double HelixThe Double Helix– Complimentary Base PairingComplimentary Base Pairing

• Replication of DNAReplication of DNA– ReplicationReplication– Accuracy & RepairAccuracy & Repair

LearningLearningObjectivesObjectives

• TSW …TSW …1.1. Explain the principle function of DNAExplain the principle function of DNA

2.2. Describe the structure of DNADescribe the structure of DNA

3.3. Define the term “Define the term “complementary base complementary base pairing”pairing”

4.4. Explain the role of complimentary Explain the role of complimentary base pairing in DNA replicationbase pairing in DNA replication

5.5. Summarize the main features of DNA Summarize the main features of DNA replicationreplication

The Search for the Double The Search for the Double HelixHelix

• 18571857: G. Mendel: G. Mendel– established established principles of heredityprinciples of heredity

• 18681868: J.F. Meisher: J.F. Meisher– discovered DNAdiscovered DNA in fish sperm & human in fish sperm & human

WBCsWBCs• 1910s1910s: W.H. Bragg & W.L. Bragg: W.H. Bragg & W.L. Bragg

– developed developed X-ray crystallographyX-ray crystallography• 1910s1910s: T.H. Morgan: T.H. Morgan

– established that genetic information is established that genetic information is carried on carried on chromosomeschromosomes

– unknown: DNA component? or protein unknown: DNA component? or protein component?component?

Nobel Prize 1915 - PhysicsNobel Prize 1915 - Physics

Nobel Prize 1933 – Medicine & PhysiologyNobel Prize 1933 – Medicine & Physiology


• 19281928: F. Griffith: F. Griffith– established that chemical components of established that chemical components of

dead bacterial cells could the affect dead bacterial cells could the affect genotype & phenotype of living bacterial genotype & phenotype of living bacterial cells - cells - transformationtransformation

• 19441944: O. Avery, M. McCarty, & C. : O. Avery, M. McCarty, & C. MacCleodMacCleod– established that established that DNADNA is the is the transforming transforming

agentagent in bacteria in bacteria• 19471947: E. Chargaff: E. Chargaff

– established that the established that the nitrogenous basesnitrogenous bases in in DNA exist in rough equivalence according to DNA exist in rough equivalence according to the following: the following: A = T & G = CA = T & G = C

Griffith’s ExperimentGriffith’s Experiment


• 19511951: Linus Pauling: Linus Pauling– used chemical analyses & used chemical analyses & molecular molecular

modelingmodeling techniques to establish the techniques to establish the structure of the alpha helix in proteinsstructure of the alpha helix in proteins

• 1951-521951-52: M. Wilkins: M. Wilkins– developed techniques to developed techniques to crystallize DNAcrystallize DNA

and study its structure with X-raysand study its structure with X-rays• 19521952: A. Hershey & M. Chase: A. Hershey & M. Chase

– confirmed that confirmed that DNA DNA is theis the hereditary hereditary moleculemolecule using radioisotope tags of DNA using radioisotope tags of DNA & protein& protein

Nobel Prize 1954 - ChemistryNobel Prize 1954 - Chemistry

Nobel Prize 1962 - Medicine & PhysiologyNobel Prize 1962 - Medicine & Physiology

Hershey-Chase Hershey-Chase ExperimentExperiment


• 19521952: R. Franklin: R. Franklin– used X-ray crystallography to determine the used X-ray crystallography to determine the

helical structure of DNAhelical structure of DNA

• 19531953: J. Watson & F. Crick: J. Watson & F. Crick– constructed a constructed a model of DNAmodel of DNA that that

successfully explained the data of all successfully explained the data of all previous researchprevious research

– the model suggested a mechanism for :the model suggested a mechanism for : (1)(1) the the encodingencoding of an almost infinite of an almost infinite

amount of genetic informationamount of genetic information (2)(2) the requirement of hereditary molecules the requirement of hereditary molecules

to to replicatereplicate

Nobel Prize 1962 – Medicine & PhysiologyNobel Prize 1962 – Medicine & Physiology

Rosalind FranklinRosalind Franklin

X-ray diffraction photo of X-ray diffraction photo of DNADNA

James Watson & Francis James Watson & Francis CrickCrick

WatsonWatson CrickCrick

Watson & Crick’s ResultsWatson & Crick’s Results

• Double helixDouble helix – conforming to X-ray data – conforming to X-ray data• Sugar-phosphate backbonesSugar-phosphate backbones – 2; outside – 2; outside• NitrogenousNitrogenous base positionbase position – attached to – attached to

sugar-phosphate backbones; point inwardsugar-phosphate backbones; point inward• AntiparallelAntiparallel chainschains – run in opposite – run in opposite

directionsdirections• Base pairingBase pairing – hydrogen bonding: purines – hydrogen bonding: purines

of one chain to pyrimidines of opposite of one chain to pyrimidines of opposite chain; keytone forms of baseschain; keytone forms of bases A – TA – T G – C G – C

DNA Structure & FunctionDNA Structure & Function

• DDeoxyriboeoxyribonnucleic ucleic aacidcid Chemical composition: Chemical composition: CC, H, , H, OO, , NN, , PP

Polynucleotide – many Polynucleotide – many nucleotidesnucleotides Double stranded Double stranded – 2 chains– 2 chains Helical shape Helical shape – spiral– spiral

• DNA FunctionDNA Function Store & transmit hereditary informationStore & transmit hereditary information Control cell structure & chemical activity w/ Control cell structure & chemical activity w/

genetic codegenetic code

Double Double HelixHelix

Nucleotide StructureNucleotide Structure

• 5-C sugar5-C sugar deoxyribosedeoxyribose

• Phosphate groupPhosphate group -PO-PO44

• Nitrogen-containing baseNitrogen-containing base C / NC / N ring structure ring structure

5-C Sugar5-C Sugar

Phosphate Phosphate GroupGroup

Nitrogenous Nitrogenous BaseBase

Nucleotide & DNA StructurNucleotide & DNA Structuree

• To View Video:To View Video:– Move mouse cursor over slide title-linkMove mouse cursor over slide title-link– When hand appears, click onceWhen hand appears, click once

• MOV Video plays about 40 secMOV Video plays about 40 sec

Nitrogenous BasesNitrogenous Bases

• PurinesPurines:: 2 C-N rings2 C-N rings

AdenineAdenine ((AA)) GuanineGuanine ((GG))

• PyrimidinesPyrimidines:: 1 C-N ring1 C-N ring

ThymineThymine ((TT)) Cytosine Cytosine ((CC))

Polynucleotide Polynucleotide ChainChain

• Deoxyribose sugarDeoxyribose sugar ((5-C5-C))

• Phosphate groupPhosphate group ( (--POPO44))

attached to C attached to C #5#5

• Nitrogen-Nitrogen-containing basecontaining base

C-N ring(s)C-N ring(s) attached to C #1attached to C #1

Complimentary Complimentary Base PairingBase Pairing

2 H-bonds2 H-bonds

3 H-bonds3 H-bonds

AA –– T T

GG –– CC

Overall DNA StructureOverall DNA Structure

• Sides:Sides: 2 Backbones2 Backbones– AlternatingAlternating

Sugar & -PO4Sugar & -PO4

• Center:Center: Complimentary Complimentary nitrogen-containing nitrogen-containing basesbases– Variable sequencesVariable sequences– Hydrogen bonds Hydrogen bonds

holding strands holding strands togethertogether AA – – TT / / TT – – AA GG – – CC / / CC – – GG

Antiparallel Antiparallel Chains Chains –– Run in opposite directionsRun in opposite directions

3’3’ 5’5’

3’3’5’5’

DNA StructureDNA Structure



DNA ReplicationDNA Replication

• Complimentary base-pairingComplimentary base-pairing Semiconservative modelSemiconservative model

• Replication enzymesReplication enzymes Helicase Helicase DNA polymerasesDNA polymerases PrimasePrimase LigaseLigase

Replication ProcessReplication Process

• Unwinding of double helixUnwinding of double helix HelicaseHelicase – – breaks H-bondsbreaks H-bonds btw/ base btw/ base

pairs linking strandspairs linking strands

• Synthesis of new DNA strandsSynthesis of new DNA strands DNA polymeraseDNA polymerase

matches matches newnew complimentary bases to complimentary bases to old old template strandstemplate strands

Forms new DNA strandsForms new DNA strands

Unwinding Unwinding of DNA Helixof DNA Helix

helicase

helicase

DNA polymerasesDNA polymerases

Helicase & DNA PolymerasHelicase & DNA Polymerase Actione Action



Replication DiagramReplication Diagram

Semiconservative Model of Semiconservative Model of ReplicationReplication

After replicationAfter replication::

each new DNA strand containseach new DNA strand contains

1 original strand1 original strand

1 newly synthesized strand1 newly synthesized strand

The original DNA is only present as ½ of The original DNA is only present as ½ of each new strandeach new strand

Hence the termHence the term “ “semisemiconservativeconservative””

DNA Replication & Cell DivisiDNA Replication & Cell Divisionon


• MOV Video plays about 1-1/4 minMOV Video plays about 1-1/4 min

Replication BubblesReplication Bubbles

• Replication forksReplication forks – areas of – areas of synthesis of new DNAsynthesis of new DNA replication bubblesreplication bubbles allow allow

simultaneous replication to occur at simultaneous replication to occur at manymany points along moleculepoints along molecule

Reduces the amount of time Reduces the amount of time necessary for replicationnecessary for replication

Replication Forks:Replication Forks:A Closer LookA Closer Look

Replication at ForksReplication at Forks



Replication SummaryReplication Summary

DNA Replication: Leading & LDNA Replication: Leading & Lagging Strandsagging Strands



DNA Accuracy & RepairDNA Accuracy & Repair

• Replication errorsReplication errors• Post-replication errorsPost-replication errors

UV radiationUV radiation X-raysX-rays radioactive emissionsradioactive emissions chemical toxins occurring naturally in chemical toxins occurring naturally in

environment or within cellsenvironment or within cells man-made toxinsman-made toxins spontaneous interactions among spontaneous interactions among

nucleotidesnucleotides

Nucleotide Nucleotide Excision RepairExcision Repair

ProofreadingProofreading

• Polymerase enzymes Polymerase enzymes proofreadproofread DNA DNA during replicationduring replication initial pairing initial pairing errors occur once for errors occur once for

every 10,000 base pairingsevery 10,000 base pairings incorrectly matched nucleotides are incorrectly matched nucleotides are

removed & replacedremoved & replaced some errors evade proofreading:some errors evade proofreading:

mutationsmutations

Replication, Repair, & AppReplication, Repair, & Applicationslications


• ASX Video plays about 30 minASX Video plays about 30 min

RNARNA

• Structure of RNAStructure of RNA– ComponentsComponents– Types of RNATypes of RNA– Complimentary Base PairingComplimentary Base Pairing

• TranscriptionTranscription– Steps of TranscriptionSteps of Transcription– Products of TranscriptionProducts of Transcription


• TSW …TSW …1.1. Explain the primary functions of RNAExplain the primary functions of RNA

2.2. Compare the structure of RNA with Compare the structure of RNA with that of DNAthat of DNA

3.3. Describe the structure & function of Describe the structure & function of each type of RNAeach type of RNA

4.4. Summarize the process of Summarize the process of transcriptiontranscription

RNA Structure & FunctionRNA Structure & Function

• RRiboibonnucleic ucleic aacidcid Chemical composition: Chemical composition: CC, H, , H, OO, , NN, , PP

Polynucleotide – many Polynucleotide – many nucleotidesnucleotides Single stranded Single stranded – – 1 chain1 chain Three shapes Three shapes – – linearlinear, , hairpinhairpin, , globularglobular

• RNA FunctionRNA Function Transfer genetic information from DNA in Transfer genetic information from DNA in

nucleus to protein synthesis sites in cytosolnucleus to protein synthesis sites in cytosol Amino acid bindingAmino acid binding Ribosome structureRibosome structure

Nucleotide StructureNucleotide Structure

• 5-C sugar5-C sugar riboseribose

• Phosphate groupPhosphate group -PO-PO44

• Nitrogen-containing baseNitrogen-containing base C / NC / N ring structure ring structure

Phosphate Phosphate GroupGroup

OHOH Uracil (U)Uracil (U)

HH

Nitrogenous Nitrogenous BaseBase

5-Carbon Sugar5-Carbon Sugar

Nitrogenous BasesNitrogenous Bases

• PurinesPurines:: 2 C-N rings2 C-N rings

AdenineAdenine ((AA)) GuanineGuanine ((GG))

• PyrimidinesPyrimidines:: 1 C-N ring1 C-N ring

Cytosine Cytosine ((CC)) UracilUracil ((UU))

Uracil (U)Uracil (U)

HH

Types of RNATypes of RNA

• Messenger RNA (Messenger RNA (mRNAmRNA)) Shape – Shape – linear chain linear chain of variable lengthof variable length Function –Function – carries genetic code from nucleus carries genetic code from nucleus

to sire of protein synthesis in cytosolto sire of protein synthesis in cytosol

• Ribosomal RNA (Ribosomal RNA (rRNArRNA)) Shape – Shape – globular globular (mixed w/ proteins)(mixed w/ proteins) Function –Function – component of component of ribosomesribosomes where where

protein synthesis occursprotein synthesis occursProvides binding sites for mRNA & tRNAs Provides binding sites for mRNA & tRNAs

carrying amino acidscarrying amino acids

rRNArRNA

Messenger & Ribosomal Messenger & Ribosomal RNARNA

Types of RNATypes of RNA

• Transfer RNA (Transfer RNA (tRNAtRNA)) Shape – Shape – hairpin hairpin of 80 nucleotidesof 80 nucleotides Function –Function – binds to specific amino binds to specific amino

acids & carries them to site of protein acids & carries them to site of protein synthesissynthesis

45 varieties of tRNA45 varieties of tRNA

Transfer RNATransfer RNA

Amino Acid – tRNA JoiningAmino Acid – tRNA Joining

TranscriptionTranscription

• Transcription ProcessTranscription Process InitiationInitiation ElongationElongation TerminationTermination

• RNA ProcessingRNA Processing Alteration of mRNA endsAlteration of mRNA ends RNA splicingRNA splicing

Introduction to Transcription &Introduction to Transcription & Translation Translation


• ASX Video plays about 29 minASX Video plays about 29 min

DNA Transcription & mRNDNA Transcription & mRNAA



TranscriptionTranscription& Processing& Processing

• TranscriptionTranscription in nucleusin nucleus synthesis of mRNA under direction of synthesis of mRNA under direction of

DNADNA produces produces primary transcriptprimary transcript (pre- (pre-

mRNA) mRNA) • RNA processingRNA processing

in nucleusin nucleus produces produces final mRNA transcriptfinal mRNA transcript that that

exits nucleusexits nucleus

Transcription Unit Transcription Unit of a Geneof a Gene

• Transcription unitTranscription unit segmentsegment of DNAof DNA transcribed - transcribed - genegene

• PromoterPromoter region where region where transcriptiontranscription beginsbegins

• TerminatorTerminator nucleotide sequence that signals nucleotide sequence that signals endend

of transcriptionof transcription

InitiationInitiation

Transcription Transcription StepsSteps

• InitiationInitiation transcription factorstranscription factors & & RNA polymeraseRNA polymerase bind bind

to to promoter promoter (DNA)(DNA)

• ElongationElongation RNA polymeraseRNA polymerase adds RNA nucleotides to a adds RNA nucleotides to a

growing mRNA moleculegrowing mRNA molecule according the the according the the sequence of nucleotides in the DNA sequence of nucleotides in the DNA genegene

• TerminationTermination RNA polymerase RNA polymerase stopsstops at a DNA sequence at a DNA sequence

called a called a terminatorterminator

TranscriptionTranscription



Review ofReview ofNuclear StructureNuclear Structure

RNA ProcessingRNA Processing



Protein SynthesisProtein Synthesis

• Protein Structure & Composition Protein Structure & Composition • The Genetic CodeThe Genetic Code

– CodonsCodons

• TranslationTranslation– tRNA & AnticodonstRNA & Anticodons– RibosomesRibosomes– Protein AssemblyProtein Assembly


• TSW …TSW …1.1. Describe the genetic codeDescribe the genetic code

2.2. Distinguish btw/ a codon & an Distinguish btw/ a codon & an anticodon, and state where each is anticodon, and state where each is foundfound

3.3. Explain the roles of the start & stop Explain the roles of the start & stop codonscodons

4.4. Summarize the process of translationSummarize the process of translation

Protein StructureProtein Structure& Composition& Composition

• Protein PolymersProtein Polymers 1 or more1 or more polypeptides polypeptides Polypeptides =Polypeptides = sequence of amino acids sequence of amino acids

• Amino Acids (a.a.)Amino Acids (a.a.) 20 different kinds20 different kinds

• Protein FunctionProtein Function Depends on 3-dimentional structureDepends on 3-dimentional structure 3-dimensional structure depends on specific 3-dimensional structure depends on specific

a.a. sequencea.a. sequence

Amino Acid Sequence & Amino Acid Sequence & Protein StructureProtein Structure

NOTENOTE: The specific a.a. sequence comes : The specific a.a. sequence comes DIRECTLYDIRECTLY from the from the genetic code on DNA transcribed to RNAgenetic code on DNA transcribed to RNA

The Genetic CodeThe Genetic Code

• Concept Concept –– Genetic CodeGenetic Code Correlation btw/ Correlation btw/ nucleotide sequencenucleotide sequence of of

mRNAmRNA & & a.a. sequencea.a. sequence

• CodonCodon 3 3 sequentialsequential mRNAmRNA nucleotides nucleotides Each Each codoncodon codes for a codes for a specificspecific a.a.a.a.

• Evolutionary ConsiderationEvolutionary Consideration The near universality of the genetic code The near universality of the genetic code

supports the concept that all organisms are supports the concept that all organisms are evolutionarily relatedevolutionarily related

CodonsCodons

• Code redundancyCode redundancy 20 amino acids20 amino acids 64 codons64 codonsExEx: the amino acid serine has 6 : the amino acid serine has 6

different codons different codons most amino acids have 2-4 codons most amino acids have 2-4 codons

• Code redundancy is a hedge Code redundancy is a hedge against mutationagainst mutation

Not Not allall codonscodons code for a.a. code for a.a.

Genetic CodeGenetic CodeDictionary – Alternate Dictionary – Alternate

TranslationTranslation

• tRNA & AnticodonstRNA & Anticodons• RibosomesRibosomes• Protein Assembly: Translation Protein Assembly: Translation

ProcessProcess InitiationInitiation ElongationElongation TerminationTermination

• PolyribosomesPolyribosomes

Overview of Overview of TranslationTranslation

• Transfer RNATransfer RNA ((tRNAtRNA)) Amino acid Amino acid

attachment siteattachment siteBinds a.a.Binds a.a.

AnticodonAnticodonBases Bases complimentary complimentary

to mRNA codonto mRNA codon

Transfer RNA & Transfer RNA & AnticodonsAnticodons

AAGAAG

Ribosome Ribosome StructureStructure

Ribosome Function: Ribosome Function: site of protein site of protein synthesissynthesis

a.k.a., “protein a.k.a., “protein factory” of the cellfactory” of the cell

RibosomesRibosomes

• StructureStructure 2 subunits: large & small2 subunits: large & small composed:composed:

rRNArRNA proteinsproteins

• FunctionFunction: sites of activity: sites of activity small subunitsmall subunit

mRNA binding sitemRNA binding site

RibosomesRibosomes

• FunctionFunction: sites of activity: sites of activity large subunitlarge subunit

P-siteP-site: : PPeptidyl-tRNA binding site – eptidyl-tRNA binding site – tRNA tRNA w/ growing peptide chainw/ growing peptide chain

A-siteA-site: : AAminoacyl-tRNA binding site – minoacyl-tRNA binding site – tRNA w/ next a.a. for the growing peptidetRNA w/ next a.a. for the growing peptide

E-siteE-site: : EExit site – xit site – tRNA exitstRNA exits complex complex after it’s a.a. is attached to growing chainafter it’s a.a. is attached to growing chain

P AE

Ribosome Ribosome Structure & FunctionStructure & Function

Translation: Translation: Step 1Step 1

• InitiationInitiation1)1) small ribosomal subunitsmall ribosomal subunit bindsbinds to to mRNAmRNA

at 5’ capat 5’ cap

2)2) initiator tRNAinitiator tRNA (bound to methionine) (bound to methionine) bindsbinds to mRNA start codon (AUG) to mRNA start codon (AUG)

3)3) large ribosomal subunitlarge ribosomal subunit attachesattaches;;

initiation factor proteins & energy from initiation factor proteins & energy from GTP requiredGTP required

result: result: translation initiation complextranslation initiation complex


• ElongationElongation amino acids added one-by-oneamino acids added one-by-one 3-step cycle:3-step cycle:

1)1) codon recognitioncodon recognition – mRNA codon at – mRNA codon at AA site of ribosome bonds w/ anticodon site of ribosome bonds w/ anticodon of tRNA w/ a.a.of tRNA w/ a.a.

2)2) peptide bond formationpeptide bond formation – rRNA – rRNA ribozyme catalyzes peptide bond ribozyme catalyzes peptide bond formation btw a.a. of tRNA at formation btw a.a. of tRNA at AA site site and a.a. of tRNA at and a.a. of tRNA at PP site site

Translation Translation StepsSteps

• ElongationElongation3)3) translocationtranslocation – ribosome moves – ribosome moves

tRNA at tRNA at AA site w/ attached site w/ attached polypeptide to polypeptide to PP site & tRNA at site & tRNA at PP site to site to EE site where it exits the site where it exits the complex complex

elongation proceeds as ribosome elongation proceeds as ribosome “reads” mRNA“reads” mRNA from 5’ from 5’ 3’ 3’ directiondirection


• TerminationTermination1)1) stop codonstop codon (UAA, UAG, or UGA) on (UAA, UAG, or UGA) on

mRNA reachedmRNA reached

2)2) protein release factor binds to codonprotein release factor binds to codon

3)3) the translation assembly the translation assembly disassemblesdisassembles

TranslationTranslation



The Triplet CodeThe Triplet Code

PolyribosomesPolyribosomes

Transcription & Transcription & Translation in BacteriaTranslation in Bacteria

Note that both transcription & Note that both transcription & translation occur simultaneously in translation occur simultaneously in bacteria.bacteria.

Summary OfSummary Of Transcription & Transcription & TranslationTranslation

Transcription & TranslatioTranscription & Translation Reviewn Review



MutationMutation

• Point MutationsPoint Mutations base substitutionbase substitution base deletionbase deletion base insertionbase insertion

• Frameshift MutationsFrameshift Mutations Missense mutationsMissense mutations Nonsense mutationsNonsense mutations


• TSW …TSW …1.1. Explain how a base substitution in Explain how a base substitution in

DNA or RNA may effect the DNA or RNA may effect the conformation of a polypeptideconformation of a polypeptide

2.2. Explain how a base deletion or Explain how a base deletion or insertion in DNA or RNA may effect insertion in DNA or RNA may effect the functionality of a polypeptidethe functionality of a polypeptide

3.3. Distinguish btw missense & nonsense Distinguish btw missense & nonsense mutationsmutations

Point MutationsPoint Mutations

• MutationMutation – change in the genetic – change in the genetic material of a cell or virusmaterial of a cell or virus A change in A change in 1 base pair1 base pair of a gene of a gene

can lead to a mutationcan lead to a mutation Mutations in Mutations in gametesgametes or or germ cellsgerm cells

can be transmitted to offspringcan be transmitted to offspring

• OneOne change in achange in a nucleotidenucleotide can can lead to one amino acid being lead to one amino acid being substituted for anothersubstituted for another

• A A change of a single amino acidchange of a single amino acid can lead to a significant change in can lead to a significant change in polypeptide/protein structurepolypeptide/protein structure

• A small A small change in protein structurechange in protein structure can lead to a can lead to a loss of functionloss of function for for that proteinthat protein

Point Mutation:Point Mutation:Sickle-cell DiseaseSickle-cell Disease

Types ofTypes ofPoint MutationsPoint Mutations

• SubstitutionsSubstitutions– base pair substitutionbase pair substitution silent mutationsilent mutation: substitution does : substitution does

not affect a.a. sequence due to not affect a.a. sequence due to redundancy of coderedundancy of code

detectible mutationdetectible mutation: substitution : substitution causes change in a.a. sequencecauses change in a.a. sequence


• Missense mutationMissense mutation base pair substitutionbase pair substitution causes substitution of one a.a. for causes substitution of one a.a. for

anotheranother may lead to may lead to altered but functional proteinaltered but functional protein

• Nonsense mutationNonsense mutation base pair substitutionbase pair substitution changes a.a. codon to a stop codonchanges a.a. codon to a stop codon leads to leads to nonfunctional proteinnonfunctional protein


• InsertionsInsertions– additionaddition of a base pair of a base pair

• DeletionsDeletions– lossloss of a base pair of a base pair

• Frameshift mutationsFrameshift mutations– caused when the number of base pairs caused when the number of base pairs

inserted or deleted is inserted or deleted is not a multiple of not a multiple of threethree

alters the reading frame (triplet alters the reading frame (triplet grouping) of the genetic messagegrouping) of the genetic message

disastrousdisastrous effect on protein structure effect on protein structure

Consequences of Point Consequences of Point Mutations: Mutations: FrameshiftFrameshift

Deletion of UDeletion of U

Consequences of Point Consequences of Point Mutations: Mutations: FrameshiftFrameshift

Insertion of UInsertion of U

Consequences of Point Mutations: Consequences of Point Mutations: Base Pair SubstitutionBase Pair Substitution

Substitution of A Substitution of A for Gfor G


Substitution of U Substitution of U for Afor A


Substitution of U Substitution of U for Cfor C

NO EFFECTNO EFFECT

Nucleic Acids & Protein Synthesis DNA Structure & Function Replication RNA Structure & Function ...

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