You want to add D-methionine to liquid cultures of E. coli that you have grown o

Question

You want to add D-methionine to liquid cultures of E. coli that you have grown overnight to see if this unusual amino acid affects the growth rate of bacteria. To test this, you must make a 1:40 dilution of your overnight E. coli culture in fresh liquid bacterial culture media and then add the amino acid at a final concentration of 5 mM. Using a stock of D-methionine at 100 mM, how many ul (microliters) of this stock, how many ml of liquid bacterial culture media, and how many ul (microliters) of your overnight E. coli culture would you need for a final volume of 5 ml?

Explanation / Answer

Final volume = 5 ml

Amount of overnight E. coli = 1 part = 1/41 * 5 = 0.12 ml

Amount of fresh culture media = 40 parts = 40/41 * 5 = 4.88 ml.

Stock of amino acid = 100 mM.

Required final concentration = 5 mM

Strength of stock = 20x

So to obtain 5 mM in the experiment, we need to add 20 microliter of stock.

We took 41 as total parts i.e. 40+1 = 41.

Also microlitres of E.coli taken = 0.12 ml = 120 microlitres

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