GENE MUTATION
INTRODUCTION
The structure of protein molecules is related to the structure of DNA molecules. Gene
mutations are changes in DNA that cause changes in proteins and, subsequently, in heredity.
In this activity you will work through some hypothetical gene mutations.
PROCEDURE
Part I
NORMAL TRANSLATION
1. Assume that the figure below represents part of a DNA molecule. Note that the whole
molecule is much longer and the strands of deoxyribose and phosphate groups have been
omitted from the diagram.
C G A A A G G T C A T G A T C
G C T T T C C A G T A C T A G
2. Assume that mRNA is transcribed from the lower strand of DNA. Write the sequence of
mRNA codons below. Remember that mRNA codons include three nitrogenous bases.
3. Write the amino acid sequence that correlates with the mRNA codons. Refer to the amino
acid table on the last page of this worksheet.
Part II:
HYPOTHETICAL MUTATION
1. Suppose a mutagen destroys the guanine (G) at the far left of the lower DNA strand.
Write the mutated DNA molecule as a set of codons.
2. Is there a complete codon on the right end of the DNA molecule? _________
3. Write the sequence of mRNA codons that match the mutated DNA.
4. Write the amino acid sequence that correlates with the mRNA codons.
5. How do the amino acid sequences compare from part I (normal translation) and part II
(hypothetical mutation)?
_______________________________________________________________
6. Would you call part II a point mutation and/or frame-shift mutation?
_______________________________
Explain. _______________________
_______________________________________________________________
Part III: ANOTHER HYPOTHETICAL MUTATION
1. Take another look at the original DNA strand. Suppose an error occurred in the original
DNA molecule in which a “C” replaced the “T” at the third base pair from the right.
Write the mutated DNA molecule as a set of codons.
C G A A A G G T C A T G A T C
G C T T T C C A G T A C T A G
2. Write the sequence of mRNA codons that match the mutated DNA.
3. Write the amino acid sequence that correlates with the mRNA codons.
4. How do the amino acid sequences compare from part I (normal translation) and part III
(another hypothetical mutation)?
_______________________________________________________________
5. Would you call part III a point mutation and/or frame-shift mutation?
_______________________________
Explain. _______________________
_______________________________________________________________
APPLICATION
Studies of amino acid sequences in hemoglobin show that there is only one difference
between normal hemoglobin and hemoglobin found in persons who have a blood disorder
known as sickle cell anemia. The difference is the substitution of one amino acid for
another: valine for glutamic acid.
1. What two mRNA codons specify for glutamic acid? __________________________
2. What four mRNA codons specify for valine?
__________________________
3. What is the smallest base change that can account for the substitution? ___________