I. THE EUKARYOTIC CELL
A. COMPOSITION AND FUNCTIONS OF EUKARYOTIC CELLULAR STRUCTURES
3. The Endomembrane System
c. The Golgi Complex
The overall purpose of this Learning Object is to learn the chemical makeup and the functions associated with the Golgi complex in eukaryotic cells.
LEARNING OBJECTIVES FOR THIS SECTION
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.
We will now look at the Golgi complex of eukaryotic cells.
The Golgi Complex (def) (see Fig. 31, Fig. 30, and Fig. 33)
The Golgi complex or Golgi apparatus consists of 3-20 flattened and stacked saclike structures called cisternae. A complex network of tubules and vesicles is located at the edges of the cisternae. The Golgi complex functions to:
1) sort proteins and lipids received from the ER;
2) modify certain proteins and glycoproteins; and
3) sort and package these molecules into vesicles for transport to other parts of the cell or secretion from the cell.
As mentioned above, proteins that have been produced in the rough ER are placed into transition vesicles by the smooth ER. The proteins and glycoproteins within the transition vesicle are then transported to the Golgi complex as the transition vesicles fuse with the Golgi complex membrane. Here the proteins and glycoproteins may be further modified and sorted. Finally the Golgi complex will package these molecules in membrane-bound vesicles for secretion from the cell or transport to lysosomes. The vesicles involved in secretion are called secretion vesicles. These form around the molecules to be secreted as they pinch off of the Golgi complex. The secretion vesicles then fuse with the cytoplasmic membrane to release the proteins and glycoproteins from the cell (see Fig. 33).
Concept map for Eukaryotic Cell Structure
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