Final answer:
Extra-chromosomal DNA molecules separate from the main bacterial chromosome in a prokaryotic cell are called plasmids. These small, circular DNA entities can carry beneficial genes such as those conferring antibiotic resistance and can be transmitted through horizontal gene transfer.
Step-by-step explanation:
The extra-chromosomal DNA molecules in a prokaryotic cell that are separate from the single, larger DNA chromosome are called plasmids.
Plasmids are small, circular, double-stranded DNA molecules that exist independently of the bacterial chromosome. These DNA fragments are capable of autonomous replication within prokaryotic cells, such as bacteria and archaea. A unique feature of plasmids is that they often carry genes that can bestow advantageous traits to the cell, such as antibiotic resistance. This can be particularly crucial for the survival of bacteria in environments containing antibiotics. Furthermore, plasmids can be transmitted between individual cells through a process known as horizontal gene transfer, which can spread these beneficial or resistance-conferring genes throughout a bacterial population.
Plasmids form an essential part of the prokaryotic genome and are considered vital tools in molecular biology and genetics research due to their capacity to transfer genetic material between organisms, facilitating the study and manipulation of genes.