NS FL4 BIO Q54

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Vasiliy_B
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Joined: Thu Feb 21, 2019 7:36 pm

NS FL4 BIO Q54

Post by Vasiliy_B » Sat Mar 09, 2019 4:34 pm

According to the explanation, we are to find the total length of DNA by multiplying (length of one nucleotide)*(total # of nucleotides). However, shouldn't we think of one unit length of DNA as consisting of a nucleotide pair, and therefore divide the product by two to get the DNA length?

Thank you,

Vasiliy
NS_Tutor_Will
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Joined: Fri May 25, 2018 9:15 am

Re: NS FL4 BIO Q54

Post by NS_Tutor_Will » Sun Mar 10, 2019 9:15 am

Thanks for the question!

Yes, DNA will be paired, but this wouldn't affect the length from 5' to 3'. I'll try to demonstrate below:

SS DNA:

5'-TAATAAGCGC-3'

DS DNA:

5'-TAATAAGCGC-3'
3'-ATTATTCGCG-5'

These two examples have the same length despite one being single-stranded and one being double-stranded.

I hope this helps clarify it!
Vasiliy_B
Posts: 7
Joined: Thu Feb 21, 2019 7:36 pm

Re: NS FL4 BIO Q54

Post by Vasiliy_B » Thu Mar 14, 2019 5:39 pm

Hi Will,

Yes, the ssDNA and dsDNA strands will have the same length, but the dsDNA will have 20 nucleotides, while the ssDNA will have only 10 nucleotides.

If a question presented the sequence
5'-TAATAAGCGC-3'
3'-ATTATTCGCG-5'
and asked how long will it be, we would multiply (10 nucleotides)*(width of nucleotide), even though there are 20 nucleotides in total.

Paragraph 2 says that there are 6 billion nucleotides in an average human diploid cell. I assumed that it was talking about nucleotides found in double helices, which meant that the length could be found by multiplying (3 billion nucleotides)*(width of nucleotide) to get the total length.

Does my question make sense?

Thank you,

Vasiliy
NS_Tutor_Will
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Joined: Fri May 25, 2018 9:15 am

Re: NS FL4 BIO Q54

Post by NS_Tutor_Will » Sun Mar 17, 2019 8:22 am

Oh, I see! Yes that definitely makes sense. In this case, though, the questions indicates that it is just prior to mitosis, which means that there should be 6 billion base pairs (rather than the three billion base pairs that we expect). Good question! I hope this clarifies it!
Vasiliy_B
Posts: 7
Joined: Thu Feb 21, 2019 7:36 pm

Re: NS FL4 BIO Q54

Post by Vasiliy_B » Mon Mar 18, 2019 5:03 pm

Yes, since just before mitosis the DNA would have replicated. Thank you, Will!
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