Bacteria Are Grown in a Medium Containing [¹⁵N]H₄Cl for a Number

question 60

Multiple Choice

Bacteria are grown in a medium containing [¹⁵N]H₄Cl for a number of generations so that all of the DNA is made of fully 'heavy' DNA. The bacteria are moved to a new medium and grown in [¹⁴N]H₄Cl so that all subsequent new DNA will be 'light.' After one generation time, what does the DNA look like?

• A)All of the DNA is made of two 'light' strands.
• B)All of the DNA is made of two 'heavy' strands.
• C)All of the DNA is made of one 'heavy' strand and one 'light' strand.
• D)Each strand is made of a mixture of 'heavy' and 'light' DNA, with each strand being between 75% and 100% 'light.'
• E)Half of the DNA is made of two 'light' strands and half is made of two 'heavy' strands.

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