Advanced Placement (AP) Biology Practice Exam

What characterizes the chromosomal makeup of prokaryotic cells?

1. A single circular chromosome

2. Multiple linear chromosomes

3. Chromatin structure only

4. Promoter regions of genes only

The correct answer is: A single circular chromosome

Prokaryotic cells are characterized by having a single circular chromosome. This structure is quite distinct from that of eukaryotic cells, which typically contain multiple linear chromosomes housed within a nucleus. The circular chromosome in prokaryotes is not associated with histones in the same way eukaryotic DNA is packaged into chromatin. Instead, the circular DNA is compacted and held in a region of the cell called the nucleoid, which is not membrane-bound. This single circular chromosome allows prokaryotic cells to efficiently replicate their DNA and carry out essential genetic functions within their simpler cellular structure. The other options do not accurately represent prokaryotic chromosomal makeup, as prokaryotes do not possess multiple linear chromosomes, channeled chromatin structure like in eukaryotes, or exclusively promoter regions.