I. THE EUKARYOTIC CELL
A. COMPOSITION AND FUNCTIONS OF EUKARYOTIC CELLULAR STRUCTURES
4. Other Internal Membrane-Bound Organelles
c. Lysosomes, Peroxisomes, Vacuoles, and Vesicles
The overall purpose of this Learning Object is to learn the chemical makeup and the functions associated with lysosomes, peroxisomes, vacuoles, and vesicles 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 contain a variety of internal membrane-bound organelles that are not a part of the endomembrane system. These include mitochondria, chloroplasts, lysosomes, peroxisomes, vacuoles, and vesicles.
We will now look at lysosomes, peroxisomes, vacuoles, and vesicles.
Lysosomes, Peroxisomes, Vacuoles, and Vesicles
1. Lysosomes (def)
Lysosomes, synthesized by the endoplasmic reticulum and the Golgi complex, are membrane-enclosed spheres typically about 500 nanometers in diameter that contain powerful digestive enzymes. They function to digest materials that enter by endocytosis. The enzymes are called acid hydrolases because the function best at a slightly acid pH, maintained by pumping protons into the lysosome. During endocytosis, the cytoplasmic membrane invaginates and pinches off placing the ingested material in a vesicle or vacuole called an endosome. Primary lysosomes fuse with the endosome forming a secondary lysosome where the materials within are digested.
Peroxisomes are membrane-bound organelles containing an assortment of enzymes that catalyze a variety of metabolic reactions.
Proteasomes are cylindrical complexes that use ATP to digest proteins into peptides (def).
4. Vacuoles and Vesicles
Vacuoles are large membranous sacs; vesicles are smaller. Vacuoles (see Fig. 32A) are often used to store materials used for energy production such as starch, fat, or glycogen. Plant cells often contain large vacuoles filled with water. Vacuoles and vesicles also transport materials within the cell and form around particles that enter by endocytosis (def).
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