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Bacteria and Archaebacteria (Archaea) have prokaryotic cells that are simpler than animal or plant cells, and much smaller. Prokaryotic cells lack internal compartments and most organelles or cytoskeletal features. A plasma membrane is present, surrounding the cell. A cell wall is also present in most cases. A single, circular chromosome is present, containing DNA but no surrounding proteins. The chromosome is not set apart from the rest of the cell. Eukaryotic cells: Animals, plants, fungi, algae, and various other organisms have larger and more complex eukaryotic cells, about 10 times the size of bacterial cells. Eukarypotic cells have many internal compartments with specialized organelles and also a cytoskeleton. Chromosomes contain histone proteins as well as DNA. Multiple chromosomes are present, and they are linear (rod-shaped or spaghetti-shaped). The region containing chromosomes is set apart from the rest of the cell as a nucleus, enclosed by a double-layered nuclear envelope. Early microscopy (starting c. 1630): 1. A. Leeuwenhoek-- first practical microscope; discovered bacteria 2. Robert Hooke-- "Micrographia"; first described "cells" in cork The "Cell Theory" (starting c. 1830): 1. All plants are made of cells (M.J. Schleiden) 2. All animals are made of cells (T. Schwann) 3. All cells come from preexisting cells (R. Virchow)-- see below 4. All diseases are malfunctions of cells, and can be understood at the cell level (R. Virchow, "father of pathology") Cell Division: |