ABSTRACT
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2.1 CELLS, GENOMES, AND GENES
Cells are the basic units of structure and function for all living organisms. There are two types of cells: prokaryotic and eukaryotic. All prokaryotes, such as bacteria, are single-cell organisms, whereas all multi-cell organisms such as mammals are eukaryotes. One of the major differences between prokaryotic and eukaryotic cells is in the structures of membrane-restricted compartments. Prokaryotic cells lack a defined nucleus and have a single membrane-surrounded compartment. Eukaryotic cells, in contrast, have a defined nucleus and many organelles that are surrounded by a lipid membrane. These independent compartments or organelles in mammalian cells include the mitochondria, the endoplasmic reticula, the Golgi apparatus, the lysosomes, and the peroxisomes. The mitochondria are responsible for energy production; the endoplasmic reticula are involved in the synthesis of proteins and lipids and the metabolism of hormones and xenobiotics; the Golgi complexes direct protein and lipid trafficking; the lysosomes degrade worn-out cell constituents; and the peroxisomes are involved in lipid metabolism. Finally, the nucleus, although only loosely membrane-surrounded, contains the most publicized macromolecule deoxyribonucleic acid (DNA).
