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Mutations
Mutation
 Permanent changes
or errors in a DNA
sequence
 Copied during DNA
replication
 Therefore heritable
 OR may occur
during transcription
to mRNA sequence
Germ Cell Mutation
 Occur in reproductive cells of an
organism
 Will be passed on to offspring
Somatic Cell Mutation
 Occurs in body cells
 Side effects may be:
 Negative
 Positive
 There may be none
Sickle Cell Anemia
Normal hemoglobin DNA
Mutant hemoglobin DNA
mRNA
mRNA
Normal hemoglobin
Glu
Sickle-cell hemoglobin
Val
Causes
 Exposure to mutagenic agents




UV (ultraviolet) radiation
Cosmic rays
Chemicals – e.g. pesticides
X rays
Types of Mutations
Point Mutation
Chromosomal
a.k.a – Gene Mutation  Affects multiple genes
 Only one or a few
 May affect genes on
nucleotides are
separate
affected
chromosomes
Substitution
 Replacement
of one base
by another
mRNA
Protein
Met
Lys
Phe
Gly
Ala
Lys
Phe
Ser
Ala
Base substitution
Met
 AAG CCC GGC AAA
 AAG ACC GGC AAA
Possible Results
Missense mutation
 Only one amino acid is changed
DNA
CCC=
ACC=
RNA
GGG
UGG
=
=
Amino Acid
Gly
Trp
Possible Results
Nonsense Mutation
 Amino acid in middle of protein is
changed to a stop codon
 Protein not complete & inactive
DNA
GTA AGT CGG
GTA ACT CGG
=
=
Amino Acid
His – Ser - Ala
His – STOP - Ala
Possible Results
Silent Mutation
 Amino acid is not changed
DNA
CTA =
CTG =
RNA
GAU
GAC
=
=
Amino Acid
Asp
Asp
Deletion
 Elimination of one or more base pairs
AAG CCC GGC AAA
AA
CCC GGC AAA ← shift over
AAC CCG GCA AA
Addition/Insertion
 Placement of one or more base pairs
AAG CCC GGC AAA
AAG ACC CGG CAA A
Reading Frame
 The sun was hot but the old man
did not get his hat.
 Letters = base pairs (3 letters = codon)
 Words = amino acid
 Sentence = protein
 T hes unw ash otb utt heo ldm and
idn otg eth ish at.
 Th esu nwa sho tbu tth eol dma ndi
dno tge thi sha t.
Possible Results
Frameshift mutation
 Moves ‘reading frame’
 Codon = 3 bases
 Changes many amino acids
Note:
 May also result in a nonsense mutation
Deletion Mutation
 Result:
 Frameshift
mRNA
Protein
Met
Lys
Phe
Gly
Ala
Nucleotide deletion
Met
Lys
Leu
Ala
His
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 UUC
c) GCU ACU UCA AUU C
3. What was the result of each mutation?
4. Which would be most harmful?
Task
 Page 263
 Answer #2 to 7
 Omit #6(e)
 For #5: list a
maximum of 10
#2 – Additions more harmful
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 –
Nonsense vs. Missense
 Nonsense:
 Translation ends before protein is complete
 Protein = inactive
 Missense:
 One amino acid changed
 Protein = may/may not function properly
 Which is more harmful?
#4 – Causes




UV radiation
Cosmic rays
X rays
Chemicals – e.g. pesticides
#5 – Create Stop Codon
 Stop codons:
 UGA, UAA, UAG
 Change one base to become stop codon:
 UAU, UAC, UGU, UGC, UGG, UUA, UCA,
UUG, UCG, CGA, AGA, GGA, CAA, CAG,
AAA, AAG, GAA, GAG
#6(a) – Harmful?
 Original strand:
 AUG–UUU–UUG–CCU–UAU–CAU–CGU
 met–phe–leu–pro–tyr–his–arg
 Change to: UAC
 New protein:
 met–phe–leu–pro–tyr–his–arg
 Silent = not harmful
 Protein unchanged
#6(b) – Harmful?
 Original strand:
 AUG–UUU–UUG–CCU–UAU–CAU–CGU
 met–phe–leu–pro–tyr–his–arg
 Change to: UAA
 New protein:
 met–phe–leu–pro–STOP
 Nonsense = harmful
 Nonfunctioning protein
#6(c) – Harmful?
insert a C and shift over
 Original strand:
 AUG–UUU–UUG–CCU–UAU–CAU–CGU
 met–phe–leu–pro–tyr–his–arg
 New protein:
 met–phe–leu–ala–leu–leu–leu
 Frameshift mutation = harmful
 Different amino acids (new protein)
#6(d) – Harmful?
Delete and shift over
 Original strand:
 AUG–UUU–UUG–CCU–UAU–CAU–CGU
 met–phe–leu–pro–tyr–his–arg
 New protein:
 met–phe–leu–pro–ile–ile
 Frameshift mutation = harmful
 Different amino acids (new protein)
#7(a) – Single Substitution
 Arginine → Leucine
 With the following substitutions:




CGU → CUU
CGC → CUC
CGA → CUA
CGG → CUG
#7(b) – Single Substitution
 Cysteine → Glutamic acid
 Cannot be done with one base pair
substitution
#7(c) – Single Substitution
 Serine → Threonine
 With the following substitutions:






AGU → ACU
AGC → ACC
UCU → ACU
UCC → ACC
UCA → ACA
UCG → ACG
#7(d) – Single Substitution
 Isoleucine → Serine
 With the following substitutions:
 AUU → AGU
 AUC → AGC