In our lab prep space, we have the following solutions and powders: Sodium citra

Question

In our lab prep space, we have the following solutions and powders:

Sodium citrate (FW = 43.7 g/mol)

SDS powder (FW = 288.38 g/mol)

0.5 M EDTA

IPTG powder (FW = 238.3 g/mol)

20 mg/mL X-gal solution

1000X ONPG

Premade LB

Premade LB agar

0.5 mM Colchicine

50X gel running buffer

Agarose powder

95% ethanol

100 mg/mL Ampicillin

10X BamHI restriction enzyme digestion buffer

milliQ water

dimethylformamide (DMF)

1) (B-gal) How would you make 225 ml of a 100 mg/ml X-gal solution?

2) (B-gal) How would you make a 6 fold dilution of X-gal? What would the concentration of the diluted solution be?

3) transformation) If we need 2.5 L of LB + 100 mg/mL Ampicillin for all three lab sections, how much total antibiotic do we need to order? Answer in mg.

4) (transformation) How would you make 200 mL LB agar + 100 mg/mL Ampicillin?

Explanation / Answer

1) Note: it should be 10mg/ml of X-gal solution instead of 100mg/ml since the strength of the X-gal solution is 20mg/ml, therefore, any dilution you make to this stock solution will only reduce its strength from 20mg/ml.

B-gal, to make 225ml of 10mg/ml X-gal solution from 20mg/ml of X-gal solution.

Here we see the strength of the resulting solution i.e. 10mg/ml is half of the strength of the stock solution i.e. 20mg/ml. Therefore, to prepare 225 ml of 10mg/ml of X-gal solution you simply need to double the volume with miliQ water,

i.e. add 125 ml miliQ water to 125 ml of 20mg/ml of stock X-gal solution.

2) To make 6-fold diluted X-gal solution from your current stock, you simply need to add 5 parts of miliQ water to 1 part of stock X-gal solution. For example if you add 125ml of miliQ water to 25 ml of X-gal stock solution, you will get 150 ml of 6-fold diluted X-gal solution. The concentration of the resulting solution will be 1/6th of the current concentration i.e (20mg/ml)/6 = 3.34mg/ml (approximately).

3) Note, there is a typo it should be 100 micro.g/ml of Ampicillin instead of 100mg/ml.

We generally prepare 100mg/ml solution of Ampicillin which is 1000x stock solution. For final LB solution we just add 1ml of this stock Ampicillin solution.

But in this question sonce the amount of Ampicillin required is asked so we will just calculate the amount of Ampicillin required for three lab sections.

Here we need 3x 2.5L = 7.5 L of LB having 100 micro.g/ml of Ampicillin. We first need to calculate the amount of Ampicillin required to prepare 1L of 100microg/ml of Ampicillin solution. This amount is (100 microg/ml) x (1000ml) = 100000 micro.g. Therefore, amount of Ampicillin required to make 7.5L of LB stock with 100mg.ml of Ampicillin = 7.5L x 100000 = 750000 micro.g or 750mg (Note 1000micro.g = 1 mg)

4) Again it should be 100 mcro.g/ml of Ampicillin, your stock solution in the lab is 100mg/ml.

To make 200ml of LB agar + 100 micro.g/ml of Ampicillin solution, you will need to add 200 microL of your 100mg/ml Ampicillin stock solution in 200 ml of Lb agar.

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