Mutations
From Gene to Protein
Honors Biology
Ms. Kim
Mutations
• Mutations
– Are changes in the genetic material (DNA)
of a cell
2 TYPES
• 1. Point mutations can affect protein
structure and function
– Are changes in just one base pair of a gene
POINT MUTATIONS
• The change of a single
nucleotide in the DNA’s
template strand
–Can lead to the production of
–an abnormal protein or…
–the same protein
Point Mutations
• Point mutations within a gene are
called
–Base-pair substitutions
• Can result in a mutation (change)
that is
• harmful
• neutral (not harmful or helpful)
• beneficial
Substitutions
• 2 TYPES
– missense (wrong amino acid)
• ONLY 1 wrong aa is added to polypeptide…all
the other aa’s are the same
– nonsense (prematurely STOP)
• The change in DNA leads to an early STOP codon
 polypeptide is SHORTEN!!
POINT MUTATION
ANALOGY…
• TEMPLATE:
THE CAT ATE THE RAT
• POINT MUTATION: THE CAT ATE THE RAT
– THE CAT ATE THE BAT  What kind of point mutation
is this?
• MISSENSE
– THE CAT ATE THE XAT  What kind of point mutation
is this?
• NONSENSE
What is the “wobble” effect?
• The last base (nucleotide) in a codon is said to be in the
WOBBLE position.
– codon mutation may encode the same amino acid
• Leads to NEUTRAL or SILENT mutations
– Not harmful or helpful
• SILENT MUTATIONS
• Mutation does not change “end result”…change in DNA
still makes the SAME amino acid
• NO noticeable change occurs
• a change from AUU to AUC will still encode leucine
What is a neutral
mutation?
• May or may not affect the resulting protein.
– For example, if the codon AAA is mutated to AGA,
arginine would be used in the resulting protein
instead of lysine
– These amino acids are chemically similar and may
not have a large effect in the protein or its function
– IF this change causes the protein to not function (and
be LETHAL to the organism) then it is not a neutral
mutation but rather a missense mutation
2. Frameshift Mutations
• Insertions and deletions
– Are additions or losses of nucleotide pairs
in a gene
– produce frameshift mutations
• 2 TYPES
– Insertions
– Deletions
FRAMESHIFT MUTATION
ANALOGY…
• TEMPLATE:
THE CAT ATE THE RAT
• ADDITION of “B” MUTATION: THE CAT ATE THE RAT
– THE CAT BAT ETH ERA T  What kind of frameshift
mutation is this?
• INSERTION
• SUBTRACTION of “A” MUTATION: THE CAT ATE THE RAT
– THE CAT TET HER AT  What kind of frameshift
mutation is this?
• DELETION
• http://highered.mcgrawhill.com/sites/0072552980/student_view0/chapter9/animatio
n_quiz_5.html
Which is more harmful?
• Typically, frameshift mutations are more
harmful BUT some point mutations can
be LETHAL
–Ex: Tay Sachs and Cystic Fibrosis
Other Types of
Mutations
• Inversions
–“Flip Flops”
• Nucleotides trade places on each
strand
• Deletions (2+ nucleotides)
–Many nucleotides are deleted at once
Causes of Mutations
• Inherited mutations
– From mom and dad
• Spontaneous mutations
– occurs during DNA replication
• Environmental mutations
(Mutagens)
– physical or chemical agents that can cause
mutations
• Ex: Sun, viruses, chemicals
Belgian Blue Cattle (so beefy….)
The Belgian Blue has a natural
mutation in myostatin gene, which
codes for protein that inhibits
muscle development and fat
deposition (creates very lean
meat).
Piedmontese cattle
(still so beefy…)