1. Suppose that you want to purify a PCR product after gel electrophoresis. You

Question

1. Suppose that you want to purify a PCR product after gel electrophoresis. You decide to weigh an empty microcentrifuge and the wight is 1.359 g after you add the gel cut out the weight increases to 1.895 g. Based on this information what would be the volume of the QG buffer added in order to help dissolve the gel?

Select one:

a. 1.25 ml

c. 1.0 ml

d. 136 µl

e. 1.6 ml

f. 1.4 ml

2. What was the purpose of mixing the PCR sample with the loading buffer.

Select one:

a. The protocol states that the loading buffer should be added

b. To promote that the DNA settles at the bottom of the well

d. None of the choices are correct

Explanation / Answer

Ans 1- option E (1.6ml)

According to the standardized protocol the volume of QG buffer to the gel weight should be 3:1 i.e 3ml of QG buffer in 1ml or 1mg gel.

Hence to find out the weight of gel

Weight of tube containing gel- weight of empty tube

1.895g-1.359g= 0.536g of gel

Hence for 0.536 g of gel three times of QG buffer i.e

0.536*3= 1.6

1.6 ml of QG buffer must be added to dissolve the gel.

Ans 2 - option B

Loading buffer contains tracking dye and glycerol which increases the density of the sample so that the sample settles down at the bottom of well and tracking dye gives an indication about the distance travelled by the PCR samples on the running gel. Hence for these two reasons loading buffer is mixed with PCR samples.

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