Sadjan_Stevens
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I was doing some exam questions (links below), although on question 3d the mark scheme clearly states 'only the 3’ end can bind with active site of enzyme / active site of DNA polymerase,' on the other hand, question 5c's mark scheme claims 'with reference to DNA polymerase; specific; only complementary with / binds to 5’ end (of strand).' Does polymerase bind to 'only the 3' end' or is it so that it 'only binds to 5' end?' Are these not real exam questions? Obviously I am missing something.Questions: https://pmt.physicsandmathstutor.com.../Set-B/Nucleic Acids - Structure and Replication QP.pdfMark Scheme: https://pmt.physicsandmathstutor.com.../Set-B/Nucleic Acids - Structure and Replication MS.pdf
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stephsmhb
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(Original post by Sadjan_Stevens)
I was doing some exam questions (links below), although on question 3d the mark scheme clearly states 'only the 3’ end can bind with active site of enzyme / active site of DNA polymerase,' on the other hand, question 5c's mark scheme claims 'with reference to DNA polymerase; specific; only complementary with / binds to 5’ end (of strand).' Does polymerase bind to 'only the 3' end' or is it so that it 'only binds to 5' end?' Are these not real exam questions? Obviously I am missing something.Questions: https://pmt.physicsandmathstutor.com.../Set-B/Nucleic Acids - Structure and Replication QP.pdfMark Scheme: https://pmt.physicsandmathstutor.com.../Set-B/Nucleic Acids - Structure and Replication MS.pdf
I think maybe why you are confused is because DNA strands are antiparallel. So although DNA polymerase binds to the 3' end on the original DNA strand, on the other strand this will be the 5' end. So the 3' end of the original DNA strand connects with the 5' end of the new DNA strand. In question 5c it's talking about new nucleotides being added which means its referencing the 2nd strand, the one being made.
So the questions and mark schemes are correct
Hope that makes sense
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Sadjan_Stevens
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(Original post by stephsmhb)
I think maybe why you are confused is because DNA strands are antiparallel. So although DNA polymerase binds to the 3' end on the original DNA strand, on the other strand this will be the 5' end. So the 3' end of the original DNA strand connects with the 5' end of the new DNA strand. In question 5c it's talking about new nucleotides being added which means its referencing the 2nd strand, the one being made.
So the questions and mark schemes are correct
Hope that makes sense
Ah ok, DNA polymerase moves along the template strand in the 3'–5' direction, forming a new strand by binding from the 5'–3' direction. Now I feel dumb. Also, it appears that my posted links are flashcards, not exam questions? ️🤦*♂️
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stephsmhb
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(Original post by Sadjan_Stevens)
Ah ok, DNA polymerase moves along the template strand in the 3'–5' direction, forming a new strand by binding from the 5'–3' direction. Now I feel dumb. Also, it appears that my posted links are flashcards, not exam questions? ️🤦*♂️
Yeah but it's fine. I already knew the exact question you were talking about because the girl I tutor asked me about it a while ago.
Hope that helped, feel free to message me if you have any more question.
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