If E. coli is grown in a ^{15}N medium for 80 | vedclass

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(D) The generation time of $E. coli$ is $20$ minutes.After $80$ minutes,the number of generations $(n)$ = $80 / 20 = 4$ generations.Starting with $1$

Vedclass · Accepted Answer

$87.5 \%, 12.5 \%$

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(D) The generation time of $E. coli$ is $20$ minutes.After $80$ minutes,the number of generations $(n)$ = $80 / 20 = 4$ generations.Starting with $1$ molecule of $^{14}N$ $DNA$ (light),after $n$ generations,the total number of $DNA$ molecules is $2^n = 2^4 = 16$.In semi-conservative replication,only $2$ molecules will be hybrid $(^{14}N-^{15}N)$ and the remaining $(2^n - 2)$ will be heavy $(^{15}N-^{15}N)$.However,the question asks for the ratio of light to hybrid $DNA$ when starting from $^{14}N$ and moving to $^{15}N$. Wait,if we start with $^{14}N$ and move to $^{15}N$,there will be $NO$ light $DNA$ after the first generation.Re-evaluating: If the question implies starting with $^{15}N$ and moving to $^{14}N$ (Meselson-Stahl experiment standard),then after $4$ generations ($16$ molecules total):Hybrid $(^{14}N-^{15}N)$ = $2$ molecules.Light $(^{14}N-^{14}N)$ = $16 - 2 = 14$ molecules.Ratio of Light to Hybrid = $14 : 2 = 7 : 1$,which is $87.5 \% : 12.5 \%$.

If $E. coli$ is grown in a $^{15}N$ medium for $80$ minutes,starting from a $^{14}N$ medium,what will be the ratio of light to hybrid $DNA$ molecules obtained?

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