1. Water was added into a graduated cylinder to a level of 635 microliters. You
ID: 150321 • Letter: 1
Question
1. Water was added into a graduated cylinder to a level of 635 microliters. You place an object into the water and the level rose to 1.365 mL. Calculate the volume (in cm^3) of the object.
2. You are preparing 5 L of buffer solution for gel elctrophoresis. The buffer stock solution is 4x. What are the volumes (in mL) of water and buffer stock solution that should be resulted?
3. You are preparing a 4% agrose gel.What is the weight (in mg) of agrose gel powder that should be added to 40 mL of gel electrophoresis buffer solution?
4. You have 2 mL of ethidium bromide in a stock solution of 500 mg/mL. You need to add ethidium bromide into 100 mL electrophoresis buffer so that the final concentration of ethidium bromide is 10 micrograms/mL. What volume (in microliters) of ethidium bromide do you add to the electrophoresis buffer?
5. You are resolving DNA fragments using gel electrophoresis. The power supply measurements show that the gel electrophoresis is running at 100 V and 2000 D. What is the current (in mAmps)?
Explanation / Answer
1. The initial amount of water added to measuring cylinder = 635 ul = 0.635ml
Level of water after adding an object to measuring cylinder = 1.635 ml
Therefore the volume of the object = (1.635 / 0.635) = 2 Cm3
2. The stock solution of buffer = 4 X
The desired concentration of working solution = 1 X
The final volume of solution = 5L
M1 x V1 = M2 X V2
4X x V1 = 1X x 5000 ml
V1 = (5000 / 4 ) ml = 200 ml of Stock Solution
There we need to add 200 ml of Stock solution to 4800 ml of water to make the working concentration.
3. Amount of agarose needed to be added in 40 ml of 4% agarose gel
= (4/100) x 40
= 0.04 x 40
= 1.6 g
= 1600 mg
Therefore we need to add 1600 mg of agarose to make 40 ml of 4% Agarose Gel.
4. Etbr stock solution = 500 mg/ml
Desired working concentration = 10 mg/ml
Final volume = 100 ml
M1 x V1 = M2 x V2
500 mg/ml x V1 = 10 mg/ml x 100 ml
V1 = (1000 / 500) ml
v1 = 2 ml = 2000 ul
There fore we need to add 2000 ul of Etbr solution in the electrophoresis buffer.
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