II. THE EUKARYOTIC CELL

A. EUKARYOTIC CELL STRUCTURE

3. The Endomembrane System: an Overview

Fundamental Statement for this Learning Object:

1. The endomembrane system compartmentalizes the cell for various different but interrelated cellular functions. It consists of the nucleus, the endoplasmic reticulum, and the Golgi complex.

The cell is the basic unit of life. Based on the organization of their cellular structures, all living cells can be divided into two groups: prokaryotic and eukaryotic (also spelled procaryotic and eucaryotic). Animals, plants, fungi, protozoans, and algae all possess eukaryotic cell types. Only bacteria have prokaryotic cell types.

Eukaryotic cells are generally much larger and more complex than prokaryotic. Because of their larger size, they require a variety of specialized internal membrane-bound organelles to carry out metabolism, provide energy, and transport chemicals throughout the cell.

Eukaryotic cells possess what is referred to as an internal membrane system or endomembrane system that compartmentalizes the cell for various different but interrelated cellular functions. Some of these internal membrane-bound organelles, such as the nucleus and the endoplasmic reticulum, have direct connections to one another. Other organelles, such as the endoplasmic reticulum and the Golgi complex transport materials to other organelles in vesicles. A vesicle buds off of one organelle and transports materials when it fuses with another membrane. There are other membrane-bound organelles, such as mitochondria and chloroplasts which are self contained and are not generally thought of as part of the endomembrane system.

We will now look at the various structures that make up the endomembrane system, including the nucleus, the endoplasmic reticulum, and the Golgi complex.