Transcript Mutations -

DNA Mutations
• Remember that during DNA
replication, the DNA makes
an exact copy of itself before
it divides.
• DNA replication is not always
accurate.
• sometimes the bases get
copied wrong in the new
strand of DNA causing a
permanent change or
mutation.
• Mutation: A permanent
change in the
sequence of DNA.
• Mutations can cause the
protein to be made incorrectly.
• If the protein is made
incorrectly, it will not function
correctly
• Sometimes it will not function at
all.
There are two main types of mutations
based on the size of the mutation.
1. Point mutations
2. Chromosomal mutations.
1. Point Mutations is a mutations involving
one nucleotide (base) in a gene
• Sometimes several are involved.
Point mutations are subdivided into
groups
a.
b.
c.
d.
Substitution
Silent mutation
Deletion
insertion
a. Substitution: occurs when one base is
substituted for another during replication.
Picture the normal DNA code being a sentence:
THE DOG BIT THE CAT
A substitution would look like this:
THE DOG BIT THE CAR
The “T” in CAT was substituted with an “R”
to make a new word and give the
sentence new meaning.
Actual substitution: seventh base, the “G”
was substituted for an “A” during
replication.
Normal code
AUG UUG GGC GGA UUG UAA
Met Phe Gly Gly Leu Stop
Mutated code
AUG UUG AGC GGA UUG UAA
Met Phe Ser Gly Leu Stop
Normal code
AUG UUG GGC GGA UUG UAA
Met Phe Gly Gly Leu Stop
Mutated code
AUG UUG AGC GGA UUG UAA
Met Phe Ser Gly Leu Stop
• Notice that only one amino acid has been
changed
• because one codon on mRNA was changed.
Making Proteins
DNA:
TAC CGA TCG TGA ACT
Transcription
mRNA:
AUG GCU AGC ACU UGA
Translation
Protein:
Met-Ala-Ser-Thr-Stop
Effect of Mutation
on Protein
DNA:
TAC CGA TCG
C
TGA ACT
Transcription
mRNA:
AUG GCU G
AGC ACU UGA
Translation
Protein:
Met-Ala-Ser-Thr-Stop
Gly
• Sickle cell anemia is disease caused by a
substitution point mutation
• The gene that codes for the hemoglobin
protein on red blood cells is made
incorrectly.
Normal red blood cell
Sickle cell red blood cell
• In this gene, just one base is changed
• causes one amino acid difference in the
hemoglobin protein.
• causes the protein to fold differently and
not function properly in carrying oxygen
in the bloodstream.
VAL was substituted
for GLU causing the
cell to sickle
b. Silent mutation: a substitution where the
mutated DNA codes for the same amino acid
as the original DNA.
Example:
THE DOG BIT THE CAT
1. Change the sixth letter “G” to a “g”
A mutation would look like this
THE DOg BIT THE CAT
The sentence is the same with the same
meaning so the mutation had no effect.
Normal DNA code
AUG UUG GGC GGA UUG UAA
Met Phe Gly Gly Leu Stop
1. Substitute the sixth base to A
Mutated DNA code
AUG UUA AGC GGA UUG UAA
Met Phe Gly Gly Leu Stop
Normal DNA code
AUG UUG GGC GGA UUG UAA
Met Phe Gly Gly Leu Stop
Mutated DNA code
AUG UUA AGC GGA UUG UAA
Met Phe Gly Gly Leu Stop
• Both UUG and UUA code for Phe. Does not
change the protein thus called a silent mutation.
c. Deletion: single nucleotide (base) is deleted from
the DNA
Example:
THE DOG BIT THE CAT
1. Delete the sixth letter “G”
THE DO_ BIT THE CAT
2. The words must be read in groups of three like codons
3. Every letter shifts to the left
After the deletion and shift of letters
THE DOB ITT HEC AR
Example:
THE DOG BIT THE CAT
After the deletion
THE DOB ITT HEC AR
• Notice that a deletion causes every letter to
shift to the left
• It must be read in 3’s
• This changes every word after the deletion,
• Changes the entire sentence making it
meaningless.
Normal DNA code
AUG UUG GGC GGA UUG UAA
Met Phe Gly Gly Leu Stop
1. The eighth base gets deleted. “G”
2. Shifts the entire code to the left.
Mutated DNA code with deletion
AUG UUG GCG GAU UGU AA
Met Phe Ala Val Cys
Normal DNA code
AUG UUG GGC GGA UUG UAA
Met Phe Gly Gly Leu Stop
Mutated DNA code with deletion
AUG UUG GCG GAU UGU AA
Met Phe Ala Asp Cys
• Notice that every amino acid after the
deletion had changed
• This protein has problems.
• May not work correctly if at all.
d.
insertion: single nucleotide (base) is
inserted into the DNA.
Example:
THE DOG BIT THE CAT
1. Insert a “G” after the word THE
After the insertion
THE GDO GBI TTH ECA T
2. Every word after the insertion is
changed and the sentence has no
meaning
Normal DNA code
AUG UUG GGC GGA UUG UAA
Met Phe Gly Gly Leu Stop
1. Insert a “C” after the sixth base
2. Shifts the entire code to the right
Mutated DNA, insertion
AUG UUG CGG CGG AUU GUA A
Met Phe Arg Arg Ile
Val
Normal DNA code
AUG UUG GGC GGA UUG UAA
Met Phe Gly Gly Leu Stop
Mutated DNA, insertion
AUG UUG CGG CGG AUU GUA A
Met Phe Arg Arg Ile
Val
• Notice that every amino acid after the deletion
had changed
• This protein too has problems.
• May not work correctly if at all.
Insertions and deletions are known as frameshift
mutations.
Frameshift mutation: the insertion or
deletion causes a shift in the reading
frame of the DNA
• Deletions cause the bases to shift to the left
• Insertions cause the bases to shift to the right
• Every amino acid after the insertion or deletion
is changed
• This changes the entire polypeptide chain.
Gene Mutations:
Substitution, Insertion, and
Deletion (frameshift mutations)
Substitution
Go to
Section:
Insertion
Deletion
Chromosomal Mutations
• Chromosomal mutations:
involve changes in the
number or structure of
chromosomes.
– Changes may include:
– locations of genes on
chromosomes,
– number of copies of genes.
Four types of chromosomal mutations
1. deletion:
2. duplication:
3. inversion:
4. translocation:
Down syndrome: 47
chromosomes
1. deletion:
loss of all or part of a chromosome.
2. duplication:
segment of the chromosome is repeated.
3. inversion: part of the chromosome gets
flipped around and reattached.
4. translocation: part of one chromosome
breaks off and attaches to another
chromosome.
• How do mutations
happen?
• Many mutations are not
caused by errors in
replication.
• Mutations can be
caused by mutagens
• Mutagen: something in
the environment that
causes a mutation
Examples of mutagens
a. Ultraviolet or solar radiation (sun)
b. nuclear radiation
c. Cigarette smoke
d. X-rays
e. chemicals in the environment
There are many more
Mutations often lead to problems including
• cancer
• birth defects and
• proteins or enzymes that do not work like sickle cell
anemia.
• In rare cases, the mutation
can be beneficial.
• For example, mutation can
cause the loss of an
enzyme that makes a moth
a lighter color.
• That moth has an
advantage in light
environments.
• So in this case, the
mutation was beneficial.
• Mutations are the driving force behind
evolution.
• Over millions of years, mutations can
accumulate causes big changes and the
creation of new species.
Important:
• In order for mutations
to be passed to the
next generation, they
must be in sex cells.
• That includes sperm
and eggs.
• You cannot pass on
mutations if they
occur in the lungs or
heart.