What structure is formed by nucleosomes connected by stretches of DNA?

The structure formed by nucleosomes connected by stretches of DNA is indeed the 10 nm fiber, often referred to as "beads on a string." In this structure, nucleosomes (which are the basic units of chromatin made up of a segment of DNA wrapped around histone proteins) are separated by linker DNA. This arrangement allows for a relatively loose packaging of DNA, facilitating processes such as transcription and replication where easier access to the genetic material is needed.

The 30 nm fiber represents a higher level of chromatin organization that comes after the 10 nm fiber, where the DNA and nucleosomes are more tightly packed. This higher-order structure is crucial for further compaction of the DNA within the nucleus but is distinct from the configuration seen in the 10 nm fiber.

Understanding the formation of the 10 nm fiber is essential for grasping how DNA is organized in eukaryotic cells, as it serves as the foundation for more complex structures that allow for efficient storage and management of genetic information.