The First Cell: All present-day cells, both prokaryotes and eukaryotes, are descended from a single ancestor. The first cell is thought to have arisen at least 3.8 billion years ago as a result of enclosure of self-replicating RNA in a phospholipid membrane.
The Evolution of Metabolism: The earliest reactions for the generation of metabolic energy were a form of anaerobic glycolysis. Photosynthesis then evolved, followed by oxidative metabolism.
Present-Day Prokaryotes: Present-day prokaryotes are divided into two groups, the archaebacteria and the eubacteria, which diverged early in evolution.
Eukaryotic Cells: Eukaryotic cells, which are larger and more complex than prokaryotic cells, contain a nucleus, cytoplasmic organelles, and a cytoskeleton.
The Origin of Eukaryotes: Eukaryotic cells are thought to have evolved from symbiotic associations of prokaryotes. The genome of eukaryotes may have arisen from a fusion of eubacterial and archaebacterial genomes.
The Development of Multicellular Organisms: The simplest eukaryotes are unicellular organisms, such as yeasts and amoebas. Multicellular organisms evolved from associations between such unicellular eukaryotes, and division of labor led to the development of the many kinds of specialized cells that make up present-day plants and animals.
E. coli: Because of their genetic simplicity and ease of study, bacteria such as E. coli are particularly useful for investigation of fundamental aspects of biochemistry and molecular biology.
Yeasts: As the simplest eukaryotic cells, yeasts are an important model for studying various aspects of eukaryotic cell biology.
Caenorhabditis elegans: The nematode C. elegans is a simple multicellular organism that serves as an important model in developmental biology.
Drosophila melanogaster: Because of extensive genetic analysis, studies of the fruit fly Drosophila have led to major advances in understanding animal development.
Arabidopsis thaliana: The small flowering plant Arabidopsis is widely used as a model for studies of plant molecular biology and development.
Vertebrates: Many kinds of vertebrate cells can be grown in culture, where they can be studied under controlled laboratory conditions. Specialized cell types, such as neurons and muscle cells, provide useful models for investigating particular aspects of cell biology. The frog Xenopus laevis and zebrafish are important models for studies of early vertebrate development, and the mouse is a mammalian species suitable for genetic analysis.
Light Microscopy: A variety of methods are used to visualize cells and subcellular structures and to determine the intracellular localization of specific molecules using the light microscope.
Electron Microscopy: Electron microscopy, with a resolution that is approximately a hundredfold greater than that of light microscopy, is used to analyze details of cell structure.
Subcellular Fractionation: The organelles of eukaryotic cells can be isolated for biochemical analysis by differential centrifugation.
Growth of Animal Cells in Culture: The propagation of animal cells in culture has allowed studies of the mechanisms that control cell growth and differentiation.
Culture of Plant Cells: Cultured plant cells can differentiate to form specialized cell types and, in some cases, can regenerate entire plants.
Viruses: Viruses provide simple models for studies of cell function.
