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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
The Search for the Double The Search for the Double HelixHelix
• 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
The Search for the Double The Search for the Double HelixHelix
• 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
The Search for the Double The Search for the Double HelixHelix
• 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
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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
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• MOV Video plays about 30 secMOV Video plays about 30 sec
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
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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
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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
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Replication SummaryReplication Summary
DNA Replication: Leading & LDNA Replication: Leading & Lagging Strandsagging Strands
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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
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• 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
LearningLearningObjectivesObjectives
• 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
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DNA Transcription & mRNDNA Transcription & mRNAA
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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
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Review ofReview ofNuclear StructureNuclear Structure
RNA ProcessingRNA Processing
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Protein SynthesisProtein Synthesis
• Protein Structure & Composition Protein Structure & Composition • The Genetic CodeThe Genetic Code
– CodonsCodons
• TranslationTranslation– tRNA & AnticodonstRNA & Anticodons– RibosomesRibosomes– Protein AssemblyProtein Assembly
LearningLearningObjectivesObjectives
• 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
Translation: Translation: Step 2Step 2
• 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
Translation: Translation: Step 3Step 3
• 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
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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
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MutationMutation
• Point MutationsPoint Mutations base substitutionbase substitution base deletionbase deletion base insertionbase insertion
• Frameshift MutationsFrameshift Mutations Missense mutationsMissense mutations Nonsense mutationsNonsense mutations
LearningLearningObjectivesObjectives
• 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
Types ofTypes ofPoint MutationsPoint Mutations
• 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
Types ofTypes ofPoint MutationsPoint Mutations
• 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
Consequences of Point Mutations: Consequences of Point Mutations: Base Pair SubstitutionBase Pair Substitution
Substitution of U Substitution of U for Afor A
Consequences of Point Mutations: Consequences of Point Mutations: Base Pair SubstitutionBase Pair Substitution
Substitution of U Substitution of U for Cfor C
NO EFFECTNO EFFECT