How many ribosomes are actively synthesizing proteins at any instant in an E. co

Question

How many ribosomes are actively synthesizing proteins at any instant in an E. coli cell growing with a doubling time of 45-minutes? Use the following assumptions in your calculations the birth size of E. coli is 1 micron in diameter and 2 microns in length. Water content of the cell is 80% and 50% of the dry cell mass is protein/enzymes. Also, the density of cell material is approximately 1 gram per mL. Rate of amino acid addition per ribosome is 20 amino acids per second, and the average molecular weight of a free amino acid is 126.

Explanation / Answer

Assume E.coli is a cylinder :

1 x 103 kg. wet cells / m3 X 0.5 x 10-6 kg.protein / kg. dry material x 0.25 kg.dry material / kg. wet cells x 6.023 x 10 23 amino acids mol / 20 amino acids ribosome . sec = 2.08 x 104 ribosomes.

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