Mutations
Fantasy
Reality
Mutations
Mutations: a permanent and heritable change in
the nucleotide sequence of a gene. Are caused by
mutagens (x-rays and UV light)
• Substitution Mutation: One base is substituted
for a different base.
– Also known as a point mutation
Mutations
Point or Substitution mutations can affect the protein in
various ways.
•Silent Mutation:
– The mutated codon still codes for the same amino acid.
– Since there are 64 different codons but only 20 different
amino acids – more than one codon can code for the
same amino acid.
– What affect do silent mutation have on the protein.
Example
– What happens to the protein when the DNA sequence
AGA is mutated to become AGC?
Mutations
• Missense Mutation:
– The mutated DNA nucleotide changes the amino acid
in the protein.
– How is the protein affected?
Example:
– Sickle cell disease: the sixth
codon in the protein
hemoglobin, GAG, is mutated
to GTG.
– How does this mutation
change the amino sequence
in hemoglobin?
Mutations
• Nonsense Mutations
– the mutation changes a codon for an amino acid to one
of the STOP codons (TAA, TAG, or TGA).
– How is the protein affected?
Example
– Cystic Fibrosis is caused by a mutation in the gene that
codes for the CFTR gene which is made of 1408 amino
acids.
– the substitution of a T for a C at nucleotide 1609
converted a glutamine codon (CAG) to a STOP codon
(TAG).
– The protein produced by this patient had only the first 493 amino
acids of the normal chain of 1480 and could not function properly.
Mutations
• Insertions and Deletions: One base is inserted or
removed from a DNA sequence.
– Also called a Frameshift mutation:
nucleotides are read 3 nucleotides at
a time (the reading frame).
Removing or adding 1 or 2
nucleotides will change the grouping
of the nucleotides.
– How does a
frameshift mutation
affect the protein?
Mutations
Mutagens: chemicals or physical agents that
cause mutations.
• Examples: X-rays and UV light
• Mutations are random; some are beneficial
and some are harmful.
Translation
Genetic Code – the sequence of A, C, G and U
used to read the mRNA sequence.
• The genetic code is read three letters at a time.
• Each group of three mRNA nucleotides is called
a codon.
• Each codon corresponds to a single amino acid.
Chromosomal Mutations
• Chromosomal mutation: mutation
that changes the number or structure
of chromosomes.
– Deletion: The loss of all or part of a
chromosome
– Duplication: A segment is repeated
– Inversion: part of the chromosome
is reverse from its usual direction.
– Translocation: one chromosome
breaks off an attaches to another
chromosome.