I am about to do a transfection with lipofectamine on the protocol it says: For each well in a 24 well dish: a.)In one microfuge tube add I ug DNA and 50 uL OptiMEM (if none is available, you can use DMEM or RPMI without FBS or antibiotics) b.) In a second microfuge tube add I uL Lipofectamine® 2000 and 50 µL OptiMEM.
From this i thought that i just need to spec my dna samples and use the appropriate amount to make 1ug dna for example for my total dna to be 1 ug in concentration i add 7.90 ul of dna. so dont i from there just directly add 50 ul optimem as in step a of the protocol, and then do step b and mix and eventually add to wells?
i was looking at my supervisors protocol and she adds water to the dna mix to make it to a volume of 12.3ul, then she adds 37.69 ul of the optimem to dna and then 50 ul of the lipofectamine:optimem solution. My confusion is at the water step why first make it to 12.3ul?