Final Answer:
The smallest organizational unit of a chromosome is a nucleosome (Option d).
Step-by-step explanation:
A (Option d)nucleosome is the fundamental structural unit of a chromosome, consisting of DNA wound around a histone protein spool. This complex structure plays a crucial role in the organization and compaction of genetic material within the cell. The DNA wraps around the histone octamer core, forming a repeating bead-like structure, which is the nucleosome. This arrangement allows for the efficient packaging of the lengthy DNA molecule, contributing to the overall stability and functionality of chromosomes.
The nucleosome provides a hierarchical structure, serving as the basis for further chromatin organization. Multiple nucleosomes are connected by linker DNA, resembling beads on a string, forming a fiber known as chromatin. This higher-order chromatin structure can undergo dynamic changes to regulate gene expression, demonstrating the functional significance of the nucleosome in cellular processes. The term "nucleosome" accurately reflects the composition and function of this organizational unit, emphasizing the integration of DNA and histone proteins in the intricate architecture of chromosomes.
In summary, the nucleosome represents the smallest organizational unit of a chromosome, illustrating the synergistic interaction between DNA and histone proteins in maintaining the integrity and functionality of genetic material. This structural unit showcases the elegant complexity of chromatin organization within cells, fundamental to processes such as gene expression and replication.