This question is from TBR Bio book II passage I of section IX. I'm not sure if this is a mistake or not but in question #2, the answer is that the pI of HbS is slightly GREATER than the pI of HbA. However, in the explanation of question #3, it's stated that "we know the pI for HbS is slightly LESS than the pI for HbA.."😕
HbA vs. HbS
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If you are typing it exactly as it appears, then one must be a typo. However, it would be easier to explain if you provided more context.
Yea it has to be a typo. Anyway here are the details of the questions.
Question #2 is asking you to compare the pI between HbS and HbA given that HbS has a valine residue at the B-6 position of the amino acid chain whereas HbA has a glutamate residue.
Question #3 is asking you to analyze a gel electrophoresis sample. Cathode at top, anode at bottom. Two bands show. One band near top and other band near bottom. Question asks if HbA and HbS undergo gel electrophoresis at a buffered pH of 9, then the protein band shown in Lane 2 (lower band) represents:
A. HbA, because of its movement toward the negatively charged anode.
B. HbS, because of its movement towards the positively charged anode
C. HbA, because of its movement towards the positively charged anode
D. HbS, because of its movement towards the negatively charged anode.
Well, I get why its C. It's just that their explanation is throwing me off because in the previous question, the answer is that the pI of HbS is slightly greater than the pI of HbA.
Part of the explanation:
"Because HbS has a valine residue instead of a glutamate residue at the B-6 position, it is missing one negative charge. We know that the pI for HbS is slightly less than the pI for HbA; the exact pI is irrelevant. Since it is slightly less than the pI for HbA, we find that HbS, at a buffered pH of 9, is also negatively charged and migrates towards the positively charged anode."
Question #2 is asking you to compare the pI between HbS and HbA given that HbS has a valine residue at the B-6 position of the amino acid chain whereas HbA has a glutamate residue.
Question #3 is asking you to analyze a gel electrophoresis sample. Cathode at top, anode at bottom. Two bands show. One band near top and other band near bottom. Question asks if HbA and HbS undergo gel electrophoresis at a buffered pH of 9, then the protein band shown in Lane 2 (lower band) represents:
A. HbA, because of its movement toward the negatively charged anode.
B. HbS, because of its movement towards the positively charged anode
C. HbA, because of its movement towards the positively charged anode
D. HbS, because of its movement towards the negatively charged anode.
Well, I get why its C. It's just that their explanation is throwing me off because in the previous question, the answer is that the pI of HbS is slightly greater than the pI of HbA.
Part of the explanation:
"Because HbS has a valine residue instead of a glutamate residue at the B-6 position, it is missing one negative charge. We know that the pI for HbS is slightly less than the pI for HbA; the exact pI is irrelevant. Since it is slightly less than the pI for HbA, we find that HbS, at a buffered pH of 9, is also negatively charged and migrates towards the positively charged anode."
Damn! Thank you SDN. I can sleep better now. I knew there had to be some mistake in the explanation. Berkley Review, please correct that mistake. Thank you! I got the right answer for this question....but the explanation of pI of HbS v/s HbA just threw me into self doubt....
