Question

Q1.

You need to make 10 ml of a restriction enzyme buffer. You have the the following stock solutions:

50 mM Tris-HCl, 0.10 M MgCl₂, 50. mM DTT, distilled water. How much of each ingredient and water do you need to make the buffer to these final concentrations of ingredients:

·            6.0 mM Tris-HCl

·            8.0 mM MgCl₂

·            1.0 mM DTT.

How much water (in ml) do you need?

Q2.

Derrick later gets a laugh on Jenny. Jenny’s boss, Repunzelee, asks her to complete some calculations on some dilutions that Repunzelee did. This is the data:

Plate	Dilution Factor	# cfu	cfu/ml
1	1x10^6	56	A
2	3.1x10^8	31	B
3	1.0x10^5	456	C

Express the cfu/ml in proper scientific notation for cell C.

Q3.

Jenny laughs at Derrick for having done this. She tells him that he “should add a few tubes to his dilution series before transferring 0.1 ml to a plate”, if he wants to get about 30 cfu on the plate. At his current rate of dilution, how many more tubes will he need to get about 30 cfus on the plate?

Answer 1

1) Tris-HCl

stock concentration (M1)= 50 mM

final concentration (M2)= 6 mM

volume of stock required (V1)=?

final volume (V2)= 10 mL

M1V1=M2V2

V1=M2V2/M1

V1= 610/50

=1.2 mL

MgCl2

stock concentration (M1)= 0.1 M

1 M=1000 mM

0.1 M= 0.1 1000=100 mM

final concentration (M2)= 8 mM

the volume of stock required (V1)=?

final volume (V2)= 10 mL

M1V1=M2V2

V1=M2V2/M1

V1= 810/0.1

=0.8 mL

DTT

stock concentration (M1)= 50 mM

final concentration (M2)= 1 mM

volume of stock required (V1)=?

final volume (V2)=10 mL

M1V1=M2V2

V1=M2V2/M1

= 110/50

= 0.2 mL

so volume of water required= 10- volume of Tris HCl - volume of MgCl2- volume of DTT

=10-1.2-0.8-0.2

= 7.8 mL

volume of water required= 7.8 mL