Cell Biology: Eukaryotic Cells and Nucleus

Eukaryotic Cells

• The nucleus is the principal feature that distinguishes eukaryotic from prokaryotic cells.
• The nucleus serves as the repository of genetic information and as the cell's control center.
• DNA replication, transcription, and RNA processing take place within the nucleus.
• Gene expression is regulated by mechanisms unique to eukaryotes, unlike prokaryotic mRNAs.

Nuclear Envelope

• The nuclear envelope separates the nucleus from the cytoplasm and provides a structural framework for the nucleus.
• The two envelope membranes act as barriers, preventing the free passage of molecules between the nucleus and cytoplasm.
• The nuclear envelope has a complex structure consisting of two nuclear membranes, an underlying nuclear lamina, and nuclear pore complexes.
• The outer nuclear membrane is continuous with the endoplasmic reticulum, and the space between the inner and outer nuclear membranes is connected to the lumen of the endoplasmic reticulum.

Nuclear Pore Complexes

• Nuclear pore complexes are the only channels through which small polar molecules, ions, and macromolecules can travel between the nucleus and cytoplasm.
• In vertebrates, the nuclear pore complex is composed of multiple copies of about 30 different pore proteins (called nucleoporins or NUPs).
• The nuclear pore complex plays a fundamental role in the physiology of all eukaryotic cells by controlling the traffic of molecules between the nucleus and cytoplasm.

Transport of Molecules

• Small molecules and some proteins with molecular mass less than approximately 40 kd diffuse freely through the nuclear pore complex in either direction.
• Most proteins and RNAs pass through the nuclear pore complex by a selective transport process, recognized by specific signals that direct their transport.
• Several million macromolecules selectively pass between the nucleus and the cytoplasm every minute.

Selective Transport of Proteins

• Proteins imported from the cytoplasm to the nucleus are targeted by specific signals.
• These proteins are responsible for all aspects of genome structure and function, including histones, DNA polymerases, RNA polymerases, transcription factors, splicing factors, and many others.

This quiz covers the structure and function of the nucleus in eukaryotic cells, including its role in DNA replication, transcription, and gene expression. Learn about the differences between eukaryotic and prokaryotic cells.