mutations. mutation permanent changes or errors in a dna sequence copied during dna replication ...
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MutationsMutations
MutationMutation
Permanent changes Permanent changes or errors in a DNA or errors in a DNA sequencesequence
Copied during DNA Copied during DNA replicationreplication Therefore heritableTherefore heritable
OR may occur OR may occur during transcription during transcription to mRNA sequence to mRNA sequence
Germ Cell MutationGerm Cell Mutation
Occur in reproductive cells of an Occur in reproductive cells of an organismorganism
Will be passed on to offspringWill be passed on to offspring
Somatic Cell MutationSomatic Cell Mutation
Occurs in body cells Occurs in body cells
Side effects may be:Side effects may be: NegativeNegative PositivePositive There may be noneThere may be none
Normal hemoglobin Sickle-cell hemoglobin
Glu Val
Normal hemoglobin DNA Mutant hemoglobin DNA
mRNA mRNA
Sickle Cell Anemia Sickle Cell Anemia
CausesCauses
Exposure to mutagenic agentsExposure to mutagenic agents UV (ultraviolet) radiationUV (ultraviolet) radiation Cosmic raysCosmic rays Chemicals – e.g. pesticidesChemicals – e.g. pesticides X raysX rays
Types of MutationsTypes of Mutations
Point MutationPoint Mutation
a.k.a – Gene Mutationa.k.a – Gene Mutation Only one or a few Only one or a few
nucleotides are nucleotides are affectedaffected
ChromosomalChromosomal Affects multiple genesAffects multiple genes May affect genes on May affect genes on
separate separate chromosomeschromosomes
mRNA
Protein Met Lys Phe Gly Ala
Base substitution
Met Lys Phe Ser Ala
Replacement Replacement of one base of one base by anotherby another
AAG CCC GGC AAAAAG CCC GGC AAA AAG AAG AACC GGC AAACC GGC AAA
SubstitutionSubstitution
Possible ResultsPossible Results
Missense mutationMissense mutation Only one amino acid is changedOnly one amino acid is changed
DNADNA RNARNA Amino AcidAmino Acid
CCCCCC = = GGGGGG = = GlyGly
AACCCC = = UGGUGG = = TrpTrp
Possible ResultsPossible Results
Nonsense MutationNonsense Mutation Amino acid in middle of protein is Amino acid in middle of protein is
changed to a stop codonchanged to a stop codon Protein not complete & inactiveProtein not complete & inactive
DNADNA Amino AcidAmino AcidGTA AGT CGGGTA AGT CGG == His – Ser - AlaHis – Ser - AlaGTA AGTA ACCT CGGT CGG = = His – His – STOPSTOP - Ala - Ala
Possible ResultsPossible Results
Silent MutationSilent Mutation Amino acid is not changedAmino acid is not changed
DNADNA RNARNA Amino AcidAmino Acid
CTACTA = = GAUGAU = = AspAsp
CTCTGG = = GACGAC = = AspAsp
DeletionDeletion
Elimination of one or more base pairsElimination of one or more base pairs
AAAAGG CCC GGC AAA CCC GGC AAA
AA CCC GGC AAA AA CCC GGC AAA ← shift over← shift over
AAC CCG GCA AAAAC CCG GCA AA
Addition/InsertionAddition/Insertion
Placement of one or more base pairsPlacement of one or more base pairs
AAG CCC GGC AAAAAG CCC GGC AAA
AAG AAG AACC CGG CAA ACC CGG CAA A
Reading Frame Reading Frame
The sun was hot but the old man The sun was hot but the old man did not get his hat.did not get his hat.
Letters = base pairs (3 letters = codon)Letters = base pairs (3 letters = codon) Words = amino acidWords = amino acid Sentence = proteinSentence = protein
T hes unw ash otb utt heo ldm and T hes unw ash otb utt heo ldm and idn otg eth ish at.idn otg eth ish at.
Th esu nwa sho tbu tth eol dma ndi Th esu nwa sho tbu tth eol dma ndi dno tge thi sha t.dno tge thi sha t.
Possible ResultsPossible Results
Frameshift mutationFrameshift mutation Moves ‘reading frame’Moves ‘reading frame’
Codon = 3 basesCodon = 3 bases
Changes many amino acidsChanges many amino acids
Note:Note: May also result in a nonsense mutationMay also result in a nonsense mutation
Met Lys Leu Ala His
Nucleotide deletion
mRNA
Protein Met Lys Phe Gly Ala
Deletion MutationDeletion Mutation
Result:Result: FrameshiftFrameshift
mRNA = mRNA = GCU ACU CAA UUC
1. Translate the mRNA above.
2. Translate each mutated mRNA below.a) GCU ACU CGA UUC b) GCU ACG CAA UUCc) GCU ACU UCA AUU C
3. What was the result of each mutation?4. Which would be most harmful?
TaskTask
Page 263Page 263 Answer #2 to 7Answer #2 to 7
Omit #6(e)Omit #6(e)
For #5: list a For #5: list a maximum of 10 maximum of 10
#2 – Additions more harmful #2 – Additions more harmful than substitutions?than substitutions?
Substitution May be silent May change only one amino acid Result: minor protein change
Addition Changes reading frame Result: completely new protein
Exception If substitution resulted in a nonsense mutation
#3 – #3 – Nonsense vs. MissenseNonsense vs. Missense
Nonsense:Nonsense: Translation ends before protein is completeTranslation ends before protein is complete Protein = inactiveProtein = inactive
Missense:Missense: One amino acid changedOne amino acid changed Protein = may/may not function properlyProtein = may/may not function properly
Which is more harmful?Which is more harmful?
#4 – Causes #4 – Causes
UV radiationUV radiation Cosmic raysCosmic rays X raysX rays Chemicals – e.g. pesticidesChemicals – e.g. pesticides
#5 – Create Stop Codon#5 – Create Stop Codon
Stop codons: Stop codons: UGA, UAA, UAG UGA, UAA, UAG
Change one base to become stop codon: Change one base to become stop codon: UAU, UAC, UGU, UGC, UGG, UUA, UCA, UAU, UAC, UGU, UGC, UGG, UUA, UCA,
UUG, UCG, CGA, AGA, GGA, CAA, CAG, UUG, UCG, CGA, AGA, GGA, CAA, CAG, AAA, AAG, GAA, GAGAAA, AAG, GAA, GAG
#6(a) – Harmful?#6(a) – Harmful?
Original strand: Original strand: AUG–UUU–UUG–CCU–UAAUG–UUU–UUG–CCU–UAUU–CAU–CGU –CAU–CGU met–phe–leu–pro–met–phe–leu–pro–tyrtyr–his–arg–his–arg
Change to: UAChange to: UACC New protein: New protein:
met–phe–leu–pro–met–phe–leu–pro–tyrtyr–his–arg–his–arg
Silent = not harmfulSilent = not harmful Protein unchangedProtein unchanged
#6(b) – Harmful?#6(b) – Harmful?
Original strand: Original strand: AUG–UUU–UUG–CCU–UAAUG–UUU–UUG–CCU–UAUU–CAU–CGU –CAU–CGU met–phe–leu–pro–met–phe–leu–pro–tyrtyr–his–arg–his–arg
Change to: UAChange to: UAAA New protein:New protein:
met–phe–leu–pro–met–phe–leu–pro–STOPSTOP
Nonsense = harmfulNonsense = harmful Nonfunctioning proteinNonfunctioning protein
#6(c) – Harmful? #6(c) – Harmful?
Original strand: Original strand: AUG–UUU–UUG–CCU–UAU–CAU–CGU AUG–UUU–UUG–CCU–UAU–CAU–CGU met–phe–met–phe–leuleu––propro––tyrtyr––hishis––argarg
New protein: New protein: met–phe–leu–met–phe–leu–alaala––leuleu––leuleu––leu leu
Frameshift mutation = harmful Frameshift mutation = harmful Different amino acids (new protein)Different amino acids (new protein)
insert a C and shift over
#6(d) – Harmful?#6(d) – Harmful?
Original strand: Original strand: AUG–UUU–UUG–CCU–AUG–UUU–UUG–CCU–UUAU–CAU–CGU AU–CAU–CGU met–phe–leu–pro–met–phe–leu–pro–tyrtyr––hishis––argarg
New protein: New protein: met–phe–leu–pro–met–phe–leu–pro–ileile––ileile
Frameshift mutation = harmful Frameshift mutation = harmful Different amino acids (new protein)Different amino acids (new protein)
Delete and shift overand shift over
#7(a) – Single #7(a) – Single SubstitutionSubstitution
Arginine Arginine →→ Leucine Leucine With the following substitutions: With the following substitutions:
CGU CGU →→ CUU CUU CGC CGC →→ CUC CUC CGA CGA →→ CUA CUA CGG CGG →→ CUG CUG
#7(b) – Single #7(b) – Single SubstitutionSubstitution
Cysteine Cysteine →→ Glutamic acid Glutamic acid Cannot be done with one base pair Cannot be done with one base pair
substitutionsubstitution
#7(c) – Single #7(c) – Single SubstitutionSubstitution
Serine Serine →→ Threonine Threonine With the following substitutions: With the following substitutions:
AGU AGU →→ ACU ACU AGC AGC →→ ACC ACC UCU UCU → ACU→ ACU UCC UCC → ACC→ ACC UCA UCA → ACA→ ACA UCG UCG → ACG→ ACG
#7(d) – Single #7(d) – Single SubstitutionSubstitution
Isoleucine Isoleucine →→ Serine Serine With the following substitutions: With the following substitutions:
AUU AUU →→ AGU AGU AUC AUC →→ AGC AGC
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