What is the structure of the nucleus?

The structure of the nucleus is composed of various structures including: the nuclear envelope, nucleoplasm, chromatin, and nucleolus. The nucleus is a relatively large and spherical double membrane-bound organelle. It is completely surrounded by the nuclear envelope, which consists of an inner and outer membrane. The nuclear envelope is penetrated by small openings known as nuclear pores, which facilitate the transport of molecules between the nucleus and cytoplasm. The nucleoplasm is the fluid-like substance within the nucleus that contains various solutions including enzymes, ions, proteins and nucleotides. The nucleus is a distinct substructure within the nucleus, and is involved in the synthesis, processing, and assembly of ribosomal subunits in the cell. 

The nuclear matrix, also known as the nuclear scaffold, is a network of protein fibers that provide structural support to the nucleus. It assists in maintaining the shape and organization of the nucleus. Chromatin is the complex of DNA and proteins found within the nucleus. It is composed of DNA molecules wrapped around histone proteins, forming nucleosomes.