## NS FL4 BIO Q54

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

### NS FL4 BIO Q54

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
Posts: 395
Joined: Fri May 25, 2018 9:15 am

### Re: NS FL4 BIO Q54

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

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
Posts: 395
Joined: Fri May 25, 2018 9:15 am

### Re: NS FL4 BIO Q54

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

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