Proportions of Light and Hybrid Densities DNA Molecules in E. Coli

Introduction:
Escherichia coli, commonly known as E. Coli, is a type of bacteria that is found in the intestines of humans and animals. It is a gram-negative, non-spore-forming, rod-shaped bacterium. DNA replication in E. Coli is semi-conservative, which means that each daughter cell gets one strand of the parental DNA molecule and synthesizes a complementary strand to form a new DNA molecule.

Proportions of Light and Hybrid Densities DNA Molecules:
If E. Coli was allowed to grow for 80 minutes, then the proportions of light and hybrid densities DNA molecules would be as follows:

1. Light Density DNA:
Light density DNA molecules are those that contain only one parental strand and one newly synthesized strand. These molecules are formed in the early stages of DNA replication. If E. Coli was allowed to grow for 80 minutes, then the proportion of light density DNA molecules would be very small as most of the DNA molecules would have undergone replication and formed hybrid density DNA molecules.

2. Hybrid Density DNA:
Hybrid density DNA molecules are those that contain one parental strand and one newly synthesized strand. These molecules are formed during the process of DNA replication. If E. Coli was allowed to grow for 80 minutes, then the proportion of hybrid density DNA molecules would be high as most of the DNA molecules would have undergone replication.

3. Explanation:
During DNA replication, the parental DNA molecule is unwound by an enzyme called helicase. This creates a replication fork where the two strands of DNA are separated. Each separated strand serves as a template for the synthesis of a complementary strand by an enzyme called DNA polymerase. The newly synthesized strands are complementary to the parental strands, and the resulting DNA molecules contain one parental strand and one newly synthesized strand.

Conclusion:
In conclusion, if E. Coli was allowed to grow for 80 minutes, then the proportion of light density DNA molecules would be very small, and the proportion of hybrid density DNA molecules would be high as most of the DNA molecules would have undergone replication. DNA replication in E. Coli is semi-conservative, which means that each daughter cell gets one strand of the parental DNA molecule and synthesizes a complementary strand to form a new DNA molecule.

E. coli divides in 20 minutes. So, after 80 minutes there will be 4 generations . In the first generation all the strands will be hybrid (as the heavy isotopes will be incorporated in the newly synthesised strands of DNA) i.e the two DNA will be intermediate nature. In the second generation, 50% the DNA will be light and 50% will be hybrid. In the 3rd generation , 25% will be hybrid and 75% will be light and in the 4th generation 12.5% will be hybrid and 87.5% will be light strand.

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