Final answer:
Proteins known as histones are responsible for loosely packing DNA into nucleosome complexes, resembling beads on a string, and are crucial for DNA organization in cells. The correct option is a) Histones
Step-by-step explanation:
Proteins used to loosely pack DNA are called histones. Histones are DNA-binding proteins that package and order DNA into structural units known as nucleosome complexes. These complexes play a critical role in DNA organization within the cell, allowing lengthy DNA molecules to fit inside the nucleus.
The first level of DNA packing involves the winding of DNA strands around histone proteins, forming a structure that, when viewed under an electron microscope, resembles small beads on a string.
This visualization depicts nucleosomes as the 'beads' which are essentially histone proteins around which the DNA winds, while the 'string' represents the DNA itself.
Supercoiling and DNA packaging involve not just these histone proteins but also additional DNA binding proteins that facilitate the compacting of the lengthy DNA molecules necessary for them to fit within the confines of a cellular nucleus, which is a characteristic feature of eukaryotic and archaeal cells. The correct option is a) Histones