AP BIOLOGY

Detailed explanation-1: -Transcription occurs in the nucleus whereas the major mRNA decay pathways operate in the cytoplasm. As synthesis and decay processes contribute equally to maintaining mRNA levels, it is quite likely that organisms have evolved a mechanism to coordinate events in the two compartments.

Detailed explanation-2: -During transcription, a piece of DNA that codes for a specific gene is copied into messenger RNA (mRNA) in the nucleus of the cell. The mRNA then carries the genetic information from the DNA to the cytoplasm, where translation occurs.

Detailed explanation-3: -The eukaryotic nucleus therefore provides a distinct compartment within the cell, allowing transcription and splicing to proceed prior to the beginning of translation. Thus, in eukaryotes, while transcription occurs in the nucleus, translation occurs in the cytoplasm.

Detailed explanation-4: -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-5: -Transcription occurs in the nucleus and not in the cytoplasm in eukaryotes because eukaryotes store the DNA in the nucleus. In prokaryotes, there is no nucleus and the DNA is in the cytoplasm. Thus, transcription can occur in the cytoplasm as well.