calculation help please

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biology_06er
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calculation help please

Post by biology_06er » Tue Mar 04, 2008 1:56 am

Hi there,

Ive got a lab tomorrow and as Im going over the instructions something is confusing...

so we have to create a dilution series from a known stock concentration of DNA..

so to tube (1) it says to add 10u 1 of stock DNA (100ng/uL) to this tube...what i am confused about is when it says 10u (does it actually mean 10uL and is it just a printing error?)...and is the conc. of the DNA 100ng/uL meaning in 1uL of solution there is 100ng of DNA ...

ok then it says to another tube (A) add 2u 1 stock of DNA and 18uL of water to this tube
then to tube 2 add 10u 1 from tube A
to tube B add 2u 1 from tube A and 18u 1 of sterile water to this tube
to tube 3 add 10u 1 from tube B
to tube C add 2u 1 from tube B and 18u 1 water to this tube
to tube 4 add 10u 1 from tube C
then to tubes 1-4 add 2uL of gel loading dye

okkk so i get all thaaat (assuming that the printing error is correct from wat i wrote above)??? now I have to calculate the conc. in each of the tubes 1-4...and im not sure if im doing it right? can someone please tell me if ive done this correctly?

im thinking this how you do it. (for tube 2 which is essentially tube A)---10uL*100ng/uL divided by 12uL=83.33ng/uL

hence tube 3 would be 83.33ng/uL*10uL divided by 12

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mith
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Post by mith » Tue Mar 04, 2008 3:14 am

nah, you have 2ul of stock and 18 ul water so total water is 20(we're assuming the dna takes up a tiny amount of volume compared to water).

so you went from 2ul to 20 ul which is a dilution of 10.

so 100ng/ul--->10ng/ul
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biology_06er
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Re: calculation help please

Post by biology_06er » Tue Mar 04, 2008 10:52 am

thanks,

does the 2uL of gel-loading dye have any effect on the new concentration?

also, just making sure ive understood the calculation...for test tube 3 would the conc. be 10*2/20=1ng/uL??

Thanks,
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canalon
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Post by canalon » Tue Mar 04, 2008 11:30 am

Ok mith gave you the way to calculate the concentration in tubes A to C and you had the correct answer for the concentration of tubes 1 to 4.
Patrick

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any proof. (Ashley Montague)

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Post by biology_06er » Tue Mar 04, 2008 12:30 pm

Hi there,

Sorry but I'm still confused :( (probably just cos of the wording :P)...even if mith gave me the way to calc. the concs. of tubes A,B and C isn't that just the same conc. for tubes 2, 3 and 4 respectively seeing as we are just taking a volume certain volume out for the "alaphabet" tubes??

so are the concs.

Tube 1: 100ng/uL
Tube 2: 10ng/uL
Tube 3: 1ng/uL
Tube 4: 0.1ng/uL

Thanks,
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canalon
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Post by canalon » Tue Mar 04, 2008 4:09 pm

Sorry I made a mistake:
Stock is 100ng/uL
A is 10 ng/uL
B is 1ng/uL
and C is 0.1ng/uL

And tubes 1 to 4 are 10/12th of the concentration of the tubes stock to C respectively.
Patrick

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any proof. (Ashley Montague)

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