Name: ________________________
BIO300/CMPSC300
Mutation - Spring 2016
As you know from lecture, there are several types of mutation:
DELETION (a base is lost)
INSERTION (an extra base is inserted)
Deletion and insertion may cause what’s called a FRAMESHIFT, meaning the reading “frame”
changes, changing the amino acid sequence.
POINT MUTATION (one base is substituted for another)
If a point mutation changes the amino acid, it’s called a MISSENSE mutation.
If a point mutation does not change the amino acid, it’s called a SILENT mutation.
If a point mutation changes the amino acid to a “stop,” it’s called a NONSENSE mutation.
Complete the boxes below. Classify each as either Deletion, Insertion, or Substitution AND as either
frameshift, missense, silent or nonsense (hint: deletion or insertion will always be frameshift).
Original DNA Sequence:
T A C A C C T T G G C G A C G A C T
mRNA Sequence:
A U G U G G A A C C G C U G C U G A
Amino Acid Sequence:
MET -TRP- ASN - ARG- CYS - (STOP)
Mutated DNA Sequence #1:
T A C A T C T T G G C G A C G A C T
What’s the mRNA sequence? A U G U A G A A C C G C U G C U G A
What will be the amino acid sequence? MET -(STOP)
Will there likely be effects?
YES
What kind of mutation is this? POINT MUTATION- NONSENSE
Mutated DNA Sequence #2: T A C G A C C T T G G C G A C G A C T
What’s the mRNA sequence? A U G C U G G A A C C G C U G C U G A
What will be the amino acid sequence? MET - LEU -GLU– PRO-LEU-LEU
Will there likely be effects?
YES
What kind of mutation is this? INSERTION - FRAME SHIFT
Mutated DNA Sequence #3: T A C A C C T T A G C G A C G A C T
What’s the mRNA sequence? A U G U G G A A U C G C U G C U G A
What will be the amino acid sequence? MET-TRP-ASN- ARG- CYS (STOP)
Will there likely be effects?
Mutated DNA Sequence #4:
What’s the mRNA sequence?
NO
What kind of mutation is this? POINT MUTATION– SILENT
T A C A C C T T G G C G A C T A C T
A U G U G G A A C C G C U G A U G A
(Circle the change)
What will be the amino acid sequence? MET-TRP- ASN- ARG- (STOP)
Will there likely be effects?
YES
What kind of mutation is this? POINT MUTATION – NONSENSE
Original DNA Sequence:
T A C A C C T T G G C G A C G A C T
mRNA Sequence:
A U G U G G A A C C G C U G C U G A
Amino Acid Sequence:
METHIONINE-TRYPTOPHAN-ASPARAGINE-ARGININE-CYSTEINE-
Mutated DNA Sequence #5:
(STOP)
T A C A C C T T G G G A C G A C T
What will be the corresponding mRNA sequence? A U G U G G A A C C C U G C U G A
What will be the amino acid sequence? METHIONINE-TRYPTOPHAN-ASPARAGINE- PROLINE - ALANINE
Will there likely be effects?
YES
What kind of mutation is this? DELETION – FRAME SHIFT
1. Which type of mutation can cause new variations of a protein? FRAME SHIFT AND MISSENSE
2. Which type of mutation results in abnormal amino acid sequence? FRAME SHIFT, NONSENSE, AND MISSENSE
3. Which type of mutation stops the translation of the mRNA? NONSENSE
Review Questions
1. A genetics found that a particular mutation had no effect on the protein coded for by the gene What do you think
the is the most likely type of mutation in this gene? Why?
Point mutation – silent mutation.
If there was no effect on the protein coded by the gene, then the amino acid sequence must have
been the same as the original sequence. Therefore the mutation must have been a point mutation
resulting in a codon that encoded the same amino acid as the original amino acid.
2. Name one amino acid that has more than one codon. Name one amino acid that has only one codon.
Methionine and Tryptophan have only one codon. All other amino acids have more than one codon.
3. Look at the following sequence: THE FAT CAT ATE THE RAT. Delete the first “H” and regroup the letters in
groups of three. Write out the new groups of three. Does the sentence still make sense? What type of mutation is
this an example of?
TEF ATC ATE TET HER AT
This sentence no longer makes sense. This is an example of a deletion resulting in a frame shift.
4. Two of the following three RNA sequences code for the same protein – which two?
#1 AGU UUA GCA ACG AGA UCA
#2 UCG CUA GCG ACC AGU UCA
#3 AGC CUC GCC ACU CGU AGU
How many point mutations are there between the two sequences?
# 1 and # 3 have the same amino
acid sequence, therefore they code
for the same protein
10 point mutations
5. You have an RNA transcript that is 105 nucleotides long. How many amino acids will be in the resultant protein?
105/3 = 35 amino acids
6. You have an RNA transcript that is 105 nucleotides long. A frameshift mutation occurs at the 85 th nucleotide.
How many amino acids will be correct?
85/3 = 28.333
The first 28 amino acids will be correct.