The Case of the Faulty Genes Assignment
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Added on 2020-04-01
The Case of the Faulty Genes Assignment
Added on 2020-04-01
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Ch 3 Act 6 – The Case of the Faulty Genes (14 pts)At 65 years old, Henry Blake was in excellent health and enjoying his first year of retirement. Upon returning from his dream trip to the Great Barrier Reef in Australia, he noticed that his left leg was swollen just inferior to the knee. He already had scheduled an appointment for a complete physical, so he knew that in a few days he would be able to have his physician look at his leg. Dr. Strickland had been the Blake family doctor for more than 40 years. Knowing that Henry had planned to do some traveling, Dr. Strickland asked “Any chance this swelling showed up after a long flight?”“As a matter of fact it did,” Henry replied.“My gut tells me that you may have a clot in that leg, but we’ll have to have a look at it before we’ll know for sure.”Dr. Strickland knew that Henry’s family had a history of clotting disorders, and he had recently treated Henry’s brother for a deep vein thrombosis (DVT), a disorder in which blood clots form in veins deep within the leg. A DVT was confirmed by Doppler ultrasonography results and Dr. Strickland placed Henry on an anticoagulant drug called warfarin to prevent further clots from forming. Henry returned to his retirement plans but quickly found himself back in Dr. Strickland’s office after suffering from frequent nose bleeds. Laboratory tests revealed that the time it took for Henry’s bloodto clot was much longer than what would be expected for the dose of warfarin he was taking. Dr. Strickland immediately took Henry off of his warfarin treatments and asked that he come in every three days for blood tests. Dr. Strickland became concerned when Henry’s abnormal clotting results continued long after he had stopped taking warfarin. Through genetic testing, Henry was found to carry a mutation in a gene for an enzyme called CYP2C9. This particular enzyme has a role in breaking down more than 15% of the drugs currently in use. As many as 35% of people carry a slower acting form of this enzyme. The portion of Henry’s DNA that codes for the CYP2C9 enzyme contains more than 1,400 nucleotides. Henry carries two copies of the CYP2C9 gene, and the tests showed that both of them contained a mutation. (Remember that human chromosomes come in pairs, so in this case, both chromosomes had been affected.) Henry was considered a poor metabolizer (PM) because both of his CYP2C9 genes contained a mutation. *Chromosomes are made from double-stranded DNA with each strand complementary to the other. One strand often is referred to as the “coding strand” and the other the “template strand”. When DNA is used for protein synthesis, the two strands are separated and the template strand is the one used to build the mRNA. 1.Explain why someone with the type of mutations Henry has would have a higher risk of overdosing on a prescribed drug? (2 pts)
During prescription, it is assumed that an individual’s body can metabolize a drug at a given rate. A compromise in the enzyme that is responsible for the metabolism means that a ‘normal’ drug dose can become an ‘overdose’ because of the impaired metabolism. The effect of the drug may be amplified in cases where the drug is taken over a long duration because new doses are often introduced before the former doses are cleared. 2. If the DNA that codes for a particular protein has over 1400 nucleotides, what is the minimum number of amino acids you would expect to find in this protein? (2 pts)4663. In the first mutation of Henry’s CYP2C9 gene the 1075th nucleotide had changed from an adenine (A) to a cytosine (C). Such a mutation would convert an ATTtriplet code in the coding strand of the DNA molecule to CTT. Using only these three bases, demonstrate what this change would do:a. the nucleotide sequence of template strand of the gene would change from __TAA___ to __GAA____b. the mRNA that results from transcription of this tripletwould change from __AUU___ to __CUU____c. the amino acid that would be used in the protein based on this codonwould change from _isoleucene____ to ___leucene___ (Use the mRNA codon chart below for this information. ) (3pts)4. In the second mutation of Henry’s gene, the 430th nucleotide had changed from a cytosine (C) to athymine (T). This mutation converts a CGTtriplet code in the coding strand of the DNA molecule toTGT. Beginning with this triplet code on the coding strand of the DNA, demonstrate what this change would do:a. the nucleotide sequence of template strand of the gene would change from ___GCA__ to __ACA____b. the mRNA that results from transcription of this tripletwould change from __CGU___ to __UGU____c. the amino acid that would be used in a protein based on this codonwould change from __Arginine___ to __Cysteine____ (Use the mRNA codon chart below for this information. ) (3pts)
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