# Homework Help: Determining the Length of DNA Molecules Biology Lab Question

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1. Mar 21, 2012

### moonstaff

1. The problem statement, all variables and given/known data

The length of DNA helix occupied by one nucleotide pair is 3.4 A (angstrom). A human has 10^14 cells and each human cell has about 6.4 x 10^9 nucleotide pairs of DNA. What is the length of double helix that could be formed from this amount of DNA in a human individual?

2. Relevant equations

3. The attempt at a solution

I'm not sure if the below is correct, and that is why I'm asking here. The first sentence of the question was actually not part of this question, but it sounded like necessary information. I'm not sure if I was suppose to use this. Also, the lab was about finding the length of an unknown DNA molecule. This question doesn't have anything to do with the unknown, right? Thank you!

(3.4 A)(6.4 x 10^9)(10^14)= 21.76 x 10^23 A

About, 21.76 x 10^23 A of double helix can be formed from this amount of DNA in a human individual.

2. Mar 21, 2012

### epenguin

Looks OK - simple multiplication. But it might convey more more sense if you expressed the result in more suitable units.

3. Mar 21, 2012

### moonstaff

What exactly would be more suitable units? Thank you in advanced!

4. Mar 21, 2012

### epenguin

Something that would mean more to the average person!

5. Mar 21, 2012

### moonstaff

Oh I see, thank you!

6. Mar 22, 2012

### Staff: Mentor

Note: suitable unit depends on the distance. It is much easier to "feel" the length if it is expressed as 100 meters than as 105 mm, but distance between cities is much better expressed in km - 100 km is easier to understand than 105 m. When it comes to really large distances they often make more sense when expressed in astronomical units or light years (at least you can "see" them on the correct scale).