MICROANATOMY

Detailed explanation-1: -The most prominent substructure within the nucleus is the nucleolus (see Figure 8.1), which is the site of rRNA transcription and processing, and of ribosome assembly.

Detailed explanation-2: -Ribosomes are mostly constructed in the cell nucleus, but the final stages of assembly occur in the cytoplasm of the cell. A protein called Nmd3 binds to the partly constructed ribosome to export it out of the nucleus.

Detailed explanation-3: -The nucleolus is formed by the secondary constriction. The nucleolus is the largest structure present in the nucleus of eukaryotic cells where it primarily serves as the site of ribosome synthesis and assembly.

Detailed explanation-4: -The nucleolus is the site of transcription and processing of rRNA and of assembly of preribosomal subunits. Thus it consists of ribosomal DNA, RNA, and ribosomal proteins, including RNA polymerases, imported from the cytosol.