Assume That You Grew a Culture of E

question 15

Essay

Assume that you grew a culture of E. coli for many generations in medium containing ¹⁵N (from the ammonium ion), a heavy isotope of nitrogen. You extract DNA from a portion of the culture and determine its density to be 1.723 gm/cm³ (call this sample
A). You then wash the remaining E. coli cells and grow them for one generation in ¹⁴N, extract the DNA from a portion of the culture, and determine its density to be 1.715 gm/cm³ (call this sample
B). You let the culture grow for one more generation in ¹⁴N, and extract the DNA (call this sample
C) is then heated to completely denature the double-stranded structures, cooled quickly (to keep the strands separate), and subjected to ultracentrifugation. Present the centrifugation profiles for heat-denatured DNA (samples A, B, and
C) that you would expect. Use the graph below. (Note: Although not the case, assume that single-stranded DNA has the same density as double-stranded DNA.)

C). Each sample of DNA (A, B, and

• A). You then wash the remaining E. coli cells and grow them for one generation in ¹⁴N, extract the DNA from a portion of the culture, and determine its density to be 1.715 gm/cm³ (call this sample
• B). You let the culture grow for one more generation in ¹⁴N, and extract the DNA (call this sample
• C) is then heated to completely denature the double-stranded structures, cooled quickly (to keep the strands separate), and subjected to ultracentrifugation. Present the centrifugation profiles for heat-denatured DNA (samples A, B, and
• C) that you would expect. Use the graph below. (Note: Although not the case, assume that single-stranded DNA has the same density as double-stranded DNA.)
• C). Each sample of DNA (A, B, and

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Definitions:

Postpartum Depression

Characteristic of women who have such strong feelings of sadness, anxiety, or despair that they have trouble coping with daily tasks during the postpartum period.

Symptoms

Signs or manifestations of a disease or disorder experienced by an individual, which are indicative of an underlying condition.

Challenges

Difficult situations that require a response or adaptation; problems that test one's ability, skill, or determination.

Organogenesis

The phase during embryonic development in which the organs of the body are formed.