Question

áctica #8 - Estructura del Ácido Nucléico, Rep... Help Save & Exit Submit Light Half-heavy Heavy McGraw-Hill Education ellook ferences Suppose that, as in the Meselson-Stahl experiment, E. coll is grown for many generations in heavy nitrogen (N) precursors, then shifted to light nitrogen (14N) precursors for 1 or 2 generations. Select the test tube that best corresponds to the positions that DNA would be expected to migrate in the following hypothetical situations. (Not all letters may be used, and some may be used more than once.) 1. DNA replication is semiconservative, and the culture was grown in light media for one generations. Click to select) 2. DNA replication is conservative, and the culture was grown in light media for one generations. (Click to select 3. DNA replication is semiconservative, and the culture was grown in light media for two generations. (Click to select) 4. DNA replication is conservative, and the culture was grown in light media for two generations. Click to select 5. DNA replication is dispersive, and the culture was grown in light media for one generations. Click to select 6. DNA replication is semiconservative, and the culture was grown in light media for one generations, then shifted back to heavy media for 1 more generation. (Click to select 7. Which tube represents the position expected if the bacteria were never shifted to light media at all? (Click to select

Answer 1

Ans:

1. B

2. A

3. C

4. A

5. B

6. D

7. E

Explanation: In semiconsevative replication, the two strand of DNA is separated and each strand serve as a template. Each newly synthesized DNA double helix contain one parental strand and one new strand. So, parental strand are half preserved. If the cells grown on heavy medium (15N), are traferred to light medium (14N). After one generation they are produce hybrid DNA (15N- 14N). After two generation on light mediun, they are produce hybrid DNA (15N- 14N) and light DNA. After one generation on light mediun if the cells are again transferred to heavy medium, they are produce hybrid DNA and heavy DNA.

In consevative replication, the two strand of DNA double helix serve as a template and one daughter cell contain parental DNA duplex and other daughter cell contain newly synthesized DNA duplex. h So, parental strand are fully preserved. If the cells grown on heavy medium, are traferred to light medium. After one generation in conservative replication, they are produce Half heavy and half light DNA, no hybrid DNA are produce. After two generation on light mediun, they are produce half heavy and half light DNA.

In dispersive replication, the two strand of DNA double helix first cuts into pieces and then rejoin. Each daughter cell contain a patchwork of parental and new DNA duplex. So, parental strand are not preserved. If the cells grown on heavy medium, are traferred to light medium. After one generation in dispersive replication, they are produce hybrid DNA.

'N medium may Heavy DNA La 1st generation Hybrid DNA medium is NI - Inn Light Hybrid 2nd medium generation - Semiconservative Semiconservative nedim. conservatione dispersine Hybrid