Transcript 25. Mutations

Mutations in the DNA &
Chromosomal Mutations
June 2, 2016
Mutations in the DNA
Protein synthesis does encounter errors
 Errors in final sequence of amino
acids can be traced to errors in the
original strand of DNA (or in
mRNA)
 Can effect the primary protein structure
and ultimately the final shape and function
of the protein
 Two types: point mutations and
frameshift mutations

A. 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
◦
mRNA
Amino Acid
In normal strand: TTC  AAG = lysine
DNA
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
Missense Mutation-replaces one
nucleotide for another and produces
a different amino acid
B. 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 codons
Insertion

NORMAL STRAND OF DNA:
TA C TT C GA C GT G A CT
T

INSERTION:
T A C TT T 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
T

DELETION:
TA C T C G A C G T GA CT

By deleting one base, the entire DNA strand is
read differently and can result in a different
final protein shape & function
Chromosomal Mutations
Entire chromosomes encounter
mutations as well
 There are 6 types:

1.
2.
3.
4.
5.
A
Deletion
Inversion
Insertion/Duplication
Translocation
Nondisjunction
B
C
D
E
Gene
Chromosome
Deletion
Before mutation
A
B
C
D
After mutation
E
A
C
D
Occurs when a single break causes a
chromosome to lose an end piece or when
two simultaneous breaks lead to loss of
internal segment
E
Inversion
Before mutation
A
B
C
D
After mutation
E
A
B
C
Occurs when a part of the chromosome
breaks off and is reinserted backwards
E
D
Insertion (duplication)
Before mutation
A
B
D
C
E
B
A
After mutation
C
B
C
B
C
D
Occurs when a part of the chromosome breaks
off & re-attaches to the same chromosome
resulting in a duplication of genes
E
Translocation
Before mutation
A
B
F
C
G
D
E
After mutation
H
F
A
B
C
G
D
E
H
Occurs when a part of one chromosome breaks
off & attaches to a non-homologous chromosome
Nondisjunction

Nondisjunction- is the failure of homologous
chromosomes or sister chromatids to separate
properly during cell division.
Nondisjunction