Introduction:
When E. coli bacteria undergoes growth, it undergoes DNA replication. During this process, the DNA molecule is duplicated to produce two identical copies. However, since the replication process is bidirectional, the DNA replication forks move in opposite directions, resulting in the formation of different regions within the DNA molecule. These regions are known as the leading and lagging strands.

Explanation:
During DNA replication, the leading strand is synthesized continuously, while the lagging strand is synthesized discontinuously in small fragments called Okazaki fragments. To understand the proportions of the light and hybrid DNA molecule after 80 minutes of growth, we need to consider the replication process.

1. Leading Strand:
The leading strand is synthesized continuously in the 5' to 3' direction, as the replication fork moves in this direction. Therefore, after 80 minutes of growth, the leading strand would be fully replicated, resulting in a complete DNA molecule. This DNA molecule is referred to as the "light" DNA molecule.

2. Lagging Strand:
The lagging strand is synthesized in short fragments in the opposite direction of the replication fork movement. These fragments are later joined together by DNA ligase to form a complete DNA strand. In the early stages of replication, the lagging strand will have more newly synthesized fragments compared to the later stages.

3. Hybrid DNA Molecule:
During DNA replication, the lagging strand contains both newly synthesized fragments and pre-existing fragments from the parental DNA molecule. These fragments form a hybrid DNA molecule that consists of a mixture of old and new DNA. After 80 minutes of growth, the lagging strand would have incorporated more newly synthesized fragments, resulting in an increased proportion of the hybrid DNA molecule.

Proportions:
After 80 minutes of growth, the proportions of the light and hybrid DNA molecules would depend on the replication progress. Since the leading strand is fully replicated, the proportion of the light DNA molecule would be 100%. On the other hand, the proportion of the hybrid DNA molecule would depend on the number of newly synthesized fragments incorporated into the lagging strand.

Conclusion:
In conclusion, after 80 minutes of growth, the proportions of the light and hybrid DNA molecules in E. coli would be 100% for the light DNA molecule and a varying proportion for the hybrid DNA molecule, depending on the progress of replication on the lagging strand.