Ten E. coli cells with ^{15}N-dsDNA are incub | vedclass

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(B) $E. coli$ replicates every $20$ minutes. In $60$ minutes, the cells will undergo $3$ rounds of replication $(60/20 = 3)$.Starting with $10$ cells,

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$60$

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(B) $E. coli$ replicates every $20$ minutes. In $60$ minutes, the cells will undergo $3$ rounds of replication $(60/20 = 3)$.Starting with $10$ cells, the total number of cells after $3$ generations is $10 	imes 2^3 = 80$ cells.In $DNA$ replication, each strand acts as a template. After $3$ generations, the number of $DNA$ molecules containing the original $^{15}N$ strand is $20$ (since only $2$ strands of the original $10$ cells' $DNA$ are conserved in the hybrid form across generations).Total $DNA$ molecules = $80 	imes 2 = 160$.$DNA$ molecules with $^{15}N$ = $20$ (as $10$ cells $	imes$ $2$ strands = $20$ original strands).$DNA$ molecules totally free from $^{15}N$ = $160 - 20 = 140$.Since each cell contains $2$ $DNA$ strands, the number of cells with $DNA$ totally free from $^{15}N$ is $140 / 2 = 70$. However, looking at the standard calculation for this specific problem type: After $n$ generations, the number of cells with only $^{14}N$ $DNA$ is $N(2^n - 2)$.For $N=10$ and $n=3$: $10 	imes (2^3 - 2) = 10 	imes (8 - 2) = 10 	imes 6 = 60$ cells.

Ten $E. coli$ cells with $^{15}N$-dsDNA are incubated in a medium containing $^{14}N$ nucleotides. After $60$ minutes, how many $E. coli$ cells will have $DNA$ totally free from $^{15}N$ (in $cells$)?

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