Bio H – Molecular Genetics
Mistakes Happen!!
What do we already know about mutations?
1. What are they and what might cause them to form?
2. Are they good? Bad? Neutral? All of the above? Explain citing specific examples with
which you are familiar.
3. Think back to our “cooking” analogy with DNA, RNA and protein. How do mutations
fit into this analogy and what would the result be?
What Categories of Mutations Are There? (you are responsible for all of these)
-
The below are categories. Depending on what the change is, a mutation might fit into
multiple categories at the same time.
Point Mutation
A point mutation: any mutation in which one base of the gene sequence is changed. A single
base can be inserted, deleted or substituted. (you may see it used synonymously with just
substitution, but the official definition is broader)
Example: Typing the word “Mog” or “Doog” when you wanted to type “Dog”.
Frame-shift mutation
Any mutation in which one or more base is inserted or deleted. It is the equivalent of adding or
removing letters in a sentence. However since the RNA sequence is read three letters at a time,
adding or removing one letter changes those groups of three, called the reading frame. That
means, that each codon following the mutation is going to be read differently.
Example: A sentence like “thecatatetherat” is broken up into a specific reading frame and read
as “The cat ate the rat.” But let’s delete the “h” in the first word. This sentence becomes “Tec
ata tet her at”. Each letter shifts over one and the sentence makes no sense.
If, however, we insert or delete 3 nucleotides (or 6, or 9) then we don’t shift the reading frame,
we just add amino acids to our protein. This could still have dire consequences. (ex: The Bad
Cat ate the rat)
Bio H – Molecular Genetics
Other types of Mutations:
- Nonsense Mutation: Any mutation that creates a stop codon earlier in the coding sequence
than it is supposed to be. This causes the protein to end before it should. This protein will end
up shortened, or truncated. This is called a nonsense mutation.
- Silent Mutation: If a point mutation changes a codon to another codon that codes the same
amino acid, then it will have no effect on the protein. This is called a silent mutation.
What do mutations do to proteins?
1. For each type of mutation NEATLY put a line through the part of the original DNA sequence
that you are mutating and replace the original sequence with your mutation.
2. NEATLY change the RNA to correspond to your mutated DNA
3. Write in the new Amino Acid sequence that is coded by your mutated DNA. You only need
to rewrite the part(s) of the sequences that are affected by the mutation.
1. Substitution – In the sequence below, create a substitution mutation. Replace one nucleotide
in the DNA with a different nucleotide
Original DNA
RNA Transcript:
Original Amino Acids
GCT
ATG
CTC
GAT
CCC
TCG
ATT
CGA
UAC
GAG
CUA
GGG
AGC
UAA
Arg
Tyr
Glu
Leu
Gly
Ser
STOP
New Amino Acids
2. Deletion – Now create a single nucleotide deletion in the second codon of the DNA
sequence.
Original DNA
RNA Transcript:
Original Amino Acids
GCT
ATG
CTC
GAT
CCC
TCG
ATT
CGA
UAC
GAG
CUA
GGG
AGC
UAA
Arg
Tyr
Glu
Leu
Gly
Ser
STOP
New Amino Acids
3. Insertion – Now create a single nucleotide insertion in the first codon of your DNA.
Original DNA
RNA Transcript:
Original Amino Acids
New Amino Acids
GCT
ATG
CTC
GAT
CCC
TCG
ATT
CGA
UAC
GAG
CUA
GGG
AGC
UAA
Arg
Tyr
Glu
Leu
Gly
Ser
STOP
Bio H – Molecular Genetics
4. Silent Mutations – time for a silent mutation. You’ll need to think about this one a little.
Remember, what ever change you make, it must still code for the same amino acid. Start by
looking at the codon charts to see which amino acids have multiple codons.
Original DNA
RNA Transcript:
Original Amino Acids
GCT
ATG
CTC
GAT
CCC
TCG
ATT
CGA
UAC
GAG
CUA
GGG
AGC
UAA
Arg
Tyr
Glu
Leu
Gly
Ser
STOP
New Amino Acids
5. Nonsense Mutations – last but not least, create a mutation in this sequence that changes the
third codon in the DNA into a stop codon.
Original DNA
RNA Transcript:
Original Amino Acids
GCT
ATG
CTC
GAT
CCC
TCG
ATT
CGA
UAC
GAG
CUA
GGG
AGC
UAA
Arg
Tyr
Glu
Leu
Gly
Ser
STOP
New Amino Acids
Discussion Questions:
1. Compare the different types of mutations and discuss whether you think one is
“worse” than the other. Support your answer with specifics about each type of
mutation.
2. Explain the evolutionary benefit to organisms having what is called a “redundant”
code, or the fact that there are multiple codons that code for the same amino acid.
Bio H – Molecular Genetics
3. The protein that I did my research on is 481 amino acids long. How long is the
RNA transcript for that protein? Careful……. 
4. Let say that the protein discussed in #3 above had a substitution that caused a
nonsense mutation at base number 333. How would the protein produced be
different? (provide specifics)
5. If there are multiple reading frames for every gene, how does the ribosome
identify which reading frame is correct?
What do mutations do to you?
Knowing what mutations do to our amino acid sequences is great, but when was the
last time you went to the doctor complaining about your proteins being made of the
wrong amino acids? Probably (hopefully?) never. For this reason we’re now going to
take a look at some specific diseases caused by such mutations and see what specific
symptoms they can cause.
1. Go to our resource page and click on “Interactive DNA, RNA and Protein” 
under “Human Health” click on “Genetic disorders” Click on “single gene
disorders”
2. “Claim” a disease from the list by writing it on the board. If your disease is
already written on the board, please select one that is not.
By the time we are “presenting” you should be able to discuss the following
1. Pronounce your disease correctly ()
2. Know what gene/protein cause the disease
3. Identify specific types of mutations that have been associated with the disease
and their inheritance pattern
4. Explain how mutations in the protein lead to the symptoms of the disease.
5. What, if anything, can be done to treat/correct the disease?
This site is just to get you started, you may venture out to other sites, just keep track of
any website from which you pull information and jot it down on your notes.