Download - Mutations
Mutationsmutations – errors in the DNA
can have a bad resultant effectcan have no effectcan have a positive resultant effect
Mutations are usually not an issue because
we have two copies of each gene.
Mutations
Changes in DNA result in:
1. silent mutations
2. missense mutations
3. nonsense mutations
Silent Mutationssilent mutation – has no effect on the function of the
cell; sequence of amino acids is not affected
often found in the non-coding regions (introns) If introns in mRNA are spliced out, then the mutation
never surfacesSome amino acids can be coded for by multiple
codons. (referred to as redundancy in the genetic code It is possible that one change in the base pair will still
produce the same amino acid
Missense Mutation
missense mutation – nucleotide sequence is changed such that a different amino acid is coded for
protein function may or may not be affected
Sickle cell anemia is a result of a missense mutation.
Sickle Cell Anemia
In the DNA, themutant templatestrand has an A where the wild-type template has a T.
The mutant mRNA has a U instead of an A in one codon.
The mutant (sickle-cell) hemoglobin has a valine (Val) instead of a glutamic acid (Glu).
Mutant hemoglobin DNAWild-type hemoglobin DNA
mRNA mRNA
Normal hemoglobin Sickle-cell hemoglobin
Glu Val
C T T C A T
G A A G U A
3 5 3 5
5 35 3
Sickle Cell Anemia
Nonsense Mutationsnonsense mutation – nucleotide sequence is
changed such that an amino acid is replaced with an early stop codon
short proteins are made; usually digested by proteases
nonsense mutations usually are lethal
Mutation
DNA: 5' - ATG ACT CAC CGA GCG CGA AGC TGA - 3‘ 3' - TAC TGA GTG GCT CGC GCT TCG ACT - 5'
mRNA: 5' - AUG ACU CAC CGA GCG CGA AGC UGA - 3' Protein: Met Thr His Arg Ala Arg Ser Stop
DNA: 5' - ATG ACT CAC TGA GCG CGA AGC TGA - 3‘ 3' - TAC TGA GTG ACT CGC GCT TCG ACT - 5‘
mRNA: 5' - AUG ACU CAC UGA GCG CGU AGC UGA - 3‘Protein: Met Thr His Stop
Template Strand
Type of DNA Change:Point Mutationspoint mutation – nucleotide changes where one
base pair (bp) is replaced by another bp
Point mutations are also known as substitution mutations.
Types of DNA Change1. Point Mutation (Base-Pair Substitution)2. Frameshift Mutation3. Chromosomal Mutation
Silent mutation
Type of DNA Change: Frameshift Mutationframeshift mutations – changes in the DNA
sequence which modify the translation reading frame
1.Deletions – removal of one or more NTs
2.Insertions – addition of one or more NTs
Type of DNA Change:Chromosomal Mutations
Sections of chromosomes can break off and reattach abnormally.
1.Translocation mutations
2.Inversion mutations
Chromosomal Mutationtranslocation mutations – large portions of DNA are
exchanged
Translocation
Chromosomal Mutationsinversion mutations – sections of a chromosome are
reversed
Causes of Mutations1. spontaneous errors due to enzymes
2. induced errors due to mutagenic agents UV radiation X-rays chemical (Agent Orange)
3. transposable elements
Spontaneous Errorsguanine may react with
water to form 8-oxo guanine
8-oxo G pairs up with adenine during replication
Transposable Elementssome DNA
sequences naturally move themselves around the genome - transposons
Classwork/HomeworkPg. 263 #1-8