A scientist investigated DNA replication in two groups of cells, labeled A and B. She injected radioactively labeled nucleotides
into cells of each group and allowed DNA replication to begin. When replication was halfway completed, she injected a drug into the cells to stop replication. She then examined the cells to determine the distribution of the newly-synthesized DNA. She found each cell of group A had many segments of new DNA in its nucleus, while each cell of group B had a single segment of new DNA in its cytoplasm. What can the researcher conclude about the cells? A. Group B cells are eukaryotic because they must have a single origin of replication. B. The cells in group A are eukaryotic because they replicate their DNA in the cytoplasm or nucleus. C. Group A cells are prokaryotic because they must have many origins of replication. D. The cells in group B are prokaryotic because they replicate their DNA in the cytoplasm.
D. The cells in group B are prokaryotic because they replicate their DNA in the cytoplasm.
Explanation:
The cells of group A are prokaryotic because it is prokaryotes which do not have a double membranous structure called nucleus for storing their genetic material. The genetic material of prokaryotes is spread in the cytoplasm in the form of a circular DNA which is called as nucleoid. Since they do not have a separate organelle like nucleus for storage of their genetic material, they are bound to replicate their DNA in the cytoplasm. In contrast to prokaryotes, eukaryotes have nucleus for storage of their genetic material and in eukaryotes replication is an exclusively nuclear event.
