DNA repeats every 10 BP!!?

[griffinss]

---

Members do not see this ad.

hi,
I am reading that DNA repeats every 10 bases because it repeats every 34 Angstrom and the distance between bases is 3.4 angstrom which makes sense but what doesn't make sense is that it REPEATS every 10 bases
I have looked up many DNA sequences but none of them repeat every 10 bases! can someone explain this concept to me please?
And it it repeats every 10 bases then there is 4^10 possibilities for different DNA so in our planet of 7billion+ there are ppl of the same DNA.. WHAT!! :S:S

 

[chaser676]

I haven't seen this material in any mcat review?

 

[griffinss]

in the princeton review book chapter 2

 

[justadream]

I believe what PR is trying to say is that there are approximately 10 BP per helical turn of the DNA. The actual BP themselves don't have to repeat.

 

[Luvahgilahsa]

hi,
I am reading that DNA repeats every 10 bases because it repeats every 34 Angstrom and the distance between bases is 3.4 angstrom which makes sense but what doesn't make sense is that it REPEATS every 10 bases
I have looked up many DNA sequences but none of them repeat every 10 bases! can someone explain this concept to me please?
And it it repeats every 10 bases then there is 4^10 possibilities for different DNA so in our planet of 7billion+ there are ppl of the same DNA.. WHAT!! :S:S

Hi I think you didn't get the idea quite right. According to my biochem class last year, B helices of DNA turns are wounded so it gets to the same spot every 10.5 bases. The DNA sequences ATGC etc are not repeated, it's just the shape of the helix that is repeated every 10 bases.

 

[gettheleadout]

I believe what PR is trying to say is that there are approximately 10 BP per helical turn of the DNA. The actual BP themselves don't have to repeat.

Yes, this is correct.

Also moving to Q&A.

 

[catzzz88]

Not the nucleotides, silly! 🙂
Go with your gut. That doesn't make sense. Ch. 2 is referring to structure.

http://www.elmhurst.edu/~chm/vchembook/582dnadoublehelix.html

"Chargaff's findings clearly indicate that some type of heterocyclic amine base pairing exists in the DNA structure. X-ray diffraction data shows that a repeating helical pattern occurs every 34 Angstrom units with 10 subunits per turn. Each subunit occupies 3.4 Angstrom units which is the same amount of space occupied by a single nucleotide unit. Using Chargaff's information and the X-ray data in conjunction with building actual molecular models, Watson and Crick developed the double helix as a model for DNA."

 

[OurTown]

They are referring to the helical structure coming full circle about every 10.4 or so base pairs. This has a lot to do with the nature of base pair stacking--the optimal stacking (to minimize steric interference, etc) is with the top base deflected about 36 degrees. This varies slightly depending on which bases are stacked, but averages 36 degrees*10 base pairs=360 degree rotation.