Several amino acid substitutions in the α and β chains of human h...

Question

Several amino acid substitutions in the α and β chains of human hemoglobin are shown in the following table.

Hb Type Normal Amino Acid Substituted Amino Acid 
Hb Toronto Ala Asp (α-5) 
HbJ Oxford Gly Asp (α-15)
Hb Mexico Gln Glu (α-54)
Hb Bethesda Tyr His (β-145)
Hb Sydney Val Ala (β-67)
HbM Saskatoon His Tyr (β-63)

Using the code table (Figure 13.7), determine how many of them can occur as a result of a single-nucleotide change.

Accepted Answer

Hi everyone. Let's take a look at this practice problem. Together we have which of the following statements is incorrect regarding the effects caused by base substitution mutation. So we need to figure out the statement that is not true. Let's review what a base substitution is. It's a simple swap of one nucleotide for another. So in this example of an M. RNA strand, the very top strand will be our original and the bottom is the mutated in the original. The mutation that occurred was a C. Became an A. So this is the location of the base substitution mutation. So having reviewed that, let's go ahead and take a look at our possible answers. We've got B transforms one code on for an amino acid into a code on for the termination of translation. So call that there are three stop code ons U A U G. A or U A. G. And this is a possibility that could happen with a base substitution. Let's look at an example. We're gonna take the code on A. Which represents slicing. If you had a base mutation and it now became you A. This is the location of the mutation and now you have a stop coat on. So B is true and therefore is not the correct answer. Now let's take a look at sea transforms one coat on for an amino acid into another coat on for the same amino acid. This is also a possibility. So we're gonna take the code on A. A. Again which represents slicing. And if it was mutated to a G. This is the location of the mutation. However, A A G also represents slicing. So there was no change in the amino acid and so C. Is also true and not the correct answer. Now we're gonna take D transforms one coat on for an amino acid into a coat on for another amino acid. And this is also true and not the right answer. An example of this happening if we took the A code on which represents slicing and it got changed to A. A. C. This would be the location of our base mutation and now A A. C. Codes for disparaging. So you had to change from life seen to disparaging. So our answer has to be a transforms the reading frame downstream of the mutant site. So recall what a reading frame is and that is how the M. RNA sequence is divided into code ons. And because every code on is three nucleotides and a base substitution would not change the overall number of nucleotides. So the number of nucleotides stays the same. The reading frame is not going to shift. The reading frame would shift if you had a nucleotide that was added or subtracted. And so a is the incorrect statement. And therefore our answer. Alright everyone. I hope you found this helpful and I'll see you soon for the next practice problem

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