Meselson and Stahlʹs Experiments Involved Growing E

question 12

Multiple Choice

Meselson and Stahlʹs experiments involved growing E. coli on a medium containing ¹⁵N heavy nitrogen) which increased the density of the bacterial DNA. Cells were then grown on a medium containing only ¹⁴N. DNA samples were obtained for analysis after one, two and three rounds of replication generations) and centrifuged on a density gradient. The double-helical DNA forms bands in the gradient depending on its density. How many bands did Meselson and Stahl see after two generation of cells were grown on the ¹⁴N medium?

• A) One with DNA containing both ¹⁵N and ¹⁴N.
• B) Two, one with DNA containing only ¹⁵N and one with DNA containing only ¹⁴N.
• C) Two, one with DNA containing both ¹⁵N and ¹⁴N and one with DNA containing only 14_N.
• D) Three, one with DNA containing only ¹⁵N, one with DNA containing both ¹⁵N and ¹⁴N and one with DNA containing only ¹⁴N.

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Definitions:

Special Instructions

Specific directions or orders given in particular situations to guide actions or procedures.

Memory Processes

The mechanisms by which information is encoded, stored, and retrieved in the brain, facilitating learning and remembering.

Control Group

In experimental research, a group of subjects that is not exposed to the treatment being tested, serving as a benchmark to measure the effects of that treatment.

Dependent Variable

The variable in an experiment that is measured or tested by the researcher to see if it is affected by changes in another variable (the independent variable).