Single nucleotide changes (point mutations) in the sequence of a gene can result
ID: 174986 • Letter: S
Question
Single nucleotide changes (point mutations) in the sequence of a gene can result in changes in the amino acid sequence of a protein produced from the mutated gene. One of the most well studied examples of the effects of a mutation on the sequence of a protein involves the oxygen-transporting protein hemoglobin. A mutation creates an altered form of hemoglobin that produces the genetic disorder called sickle-cell disease (sickle-cell anemia). You will learn more about hemoglobin and the effects of mutations in the hemoglobin gene in HemoglobinLab. The purpose of the following assignment is to demonstrate the effect of a point mutation on the amino acid sequence of a protein.
1. Sickle-cell disease results from a point mutation in the second nucleotide of the codon GAA, which results in a change in the amino acid at position 6 in the hemoglobin protein. Synthesize a mRNA from the trinucleotide sequence GAA. Enter this sequence in your notebook. Translate this mRNA and enter the results in your notebook. Synthesize and translate the trinucleotide GUA and do the same for the trinucleotide GAG. Assign codons to each amino acid produced from the three mRNA sequences. (Hint: consider what you know about the sequences for stop codons from attempting to assign codons for each amino acid.) What amino acid does the codon GAA specify? Which amino acid is incorporated into the sickle-cell hemoglobin molecule when this codon is mutated to GUA? Perform other experiments if necessary to confirm your codon assignments to answer this question.
Explanation / Answer
Normal cells
DNA CAA GTA AAC ATA GGA CTT CTT
mRNA GUU CAU UUG UAU CCU GAA GAA
protein Val His Leu Thr Pro Glu Glu
Sickle cells
DNA CAA GTA AAC ATA GGA CAT CTT
mRNA GUU CAU UUG UAU CCU GUA GAA
protein Val His Leu Thr Pro Val Glu
DNA CAA GTA AAC ATA GGA CTC CTT
mRNA GUU CAU UUG UAU CCU GAG GAA
protein Val His Leu Thr Pro Glu Glu
What amino acid does the codon GAA specify?
GAA will specify the amino acid Glu.
Which amino acid is incorporated into the sickle-cell hemoglobin molecule when this codon is mutated to GUA?
When GAA is mutated to GUA, in place of Glu, Val is substituted.
The substitution of Val in place of Glu, will make the RBC rigid and will be like stiff rods and this sickle shaped cells will stick to the vessel walls and will cause blockage.
Normal cells
DNA CAA GTA AAC ATA GGA CTT CTT
mRNA GUU CAU UUG UAU CCU GAA GAA
protein Val His Leu Thr Pro Glu Glu
Sickle cells
DNA CAA GTA AAC ATA GGA CAT CTT
mRNA GUU CAU UUG UAU CCU GUA GAA
protein Val His Leu Thr Pro Val Glu
DNA CAA GTA AAC ATA GGA CTC CTT
mRNA GUU CAU UUG UAU CCU GAG GAA
protein Val His Leu Thr Pro Glu Glu