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DNA/GENE MUTATIONS
DNA/Gene Mutations
Protein synthesis does encounter errors
 Errors in final sequence of amino acids
can be traced to errors in the original
strand of DNA
 Can effect the primary protein structure
and ultimately the final shape and function
of the protein
 Two types: point mutations and frameshift
mutations

Lets see what happens!
Look at A and locate the substitution
 Transcribe that part of the gene into the
codon it will code for.
 What amino acid should be there
normally? What amino acid is there now?

Point Mutations
Involve the substitution of one nucleotide
for another
 Three types of substitution:
1. Silent mutation
2. Nonsense mutation
3. Missense mutation

Effects vary from going unnoticed to
completely changing shape of final
protein
Silent Mutation

NORMAL STRAND OF DNA:
TA C TT C GA C GT G A CT
• SUBSTITUTED BASE PAIR:
TA C TTT GA C GT G A CT
DNA
◦
◦
Amino Acid
In normal strand: TTC  AAG = lysine
DNA
◦
mRNA
mRNA
Amino Acid
In substituted strand: TTT  AAA = lysine
Same amino acid, so there is no change in protein
structure
Nonsense Mutation

NORMAL STRAND OF DNA:
TA C TT C GA C GT G A CT

SUBSTITUTED BASE PAIR:
TA C AT C GA C GT G A CT
DNA
mRNA
Amino Acid
• In normal strand: TTC  AAG = lysine
DNA
mRNA
Amino Acid

In substituted strand: ATC  UAG = stop

Substituted base codes for a stop codon which can have
disasterous effects because the protein isn’t finished
Missense Mutation

NORMAL STRAND OF DNA:
TA C TT C GA C GT G A CT
• SUBSTITUTED BASE PAIR:
TA C T C C GA C GT G A CT
DNA
◦
mRNA
Amino Acid
In normal strand: TTC  AAG = lysine
DNA
mRNA
Amino Acid
◦
In substituted strand: TCC  AGG = arginine
◦
Different amino acid, so there is a change in protein
structure
Frameshift Mutations
Caused by either the addition or removal
of one or more nucleotides in the original
strand of DNA
 Two types:
1. Insertion
2. Deletion

Called frameshift because the addition
or removal shifts the “frame” that is
read for the amino acid codes
Insertion

NORMAL STRAND OF DNA:
TA C TT C GA C GT G A CT
C

INSERTION:
T A C TT C C G A C G T G A C T

By inserting one base, the entire DNA strand is read
differently and can result in a different final protein
shape & function
Deletion

NORMAL STRAND OF DNA:
TA C TT C GA C GT G A CT
C

DELETION:
T A C T T C G AG TG A C T

By deleting one base, the entire DNA strand is read
differently and can result in a different final protein
shape & function