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1 PROTO - Biol 2030U Fall 2010 Experiment # 1: Cellular...

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1 Biol 2030U Fall 2010 Experiment # 1: Cellular structure Introduction Introduction Cells are the structural units of all living things (with the possible exceptions of viruses and prions). Organisms are composed of either single cells or aggregations of cells. These cells are the common denominator of biology and serve to unify the broad spectrum of life ranging from microorganisms to complex higher plants and animals. - Prokaryotic cells lack a formed nucleus to house the genetic material (DNA) and nuclear proteins called histones. These cells, found only among bacteria, are small (1-5 microns), have a cell wall outside the cell membrane , lack membrane bound organelles and divide by binary fission. The cytoplasm contains large amounts of ribosomes for protein synthesis. Other cellular structures may include flagella, and/or pili. Prokaryotic cells can be classified according to their shapes: o Coccus (plural, cocci): spherical or ovoid morphology o Rod: cylindrical shape o Spirilla: spiral shape o Spirochete: tightly coiled shape o Appendage bacteria: cells that possesses extensions such as long tubes or stacks o Filamentous: long, thin cell or chains of cells - Eukaryotic cells are larger, have a membrane bound nucleus and have histones associated with the chromosomes in the nucleus. In addition to the nucleus, there are cellular membrane-bound organelles present including mitochondria, chloroplasts (in plant cells), endoplasmic reticulum, Golgi complex, lysozomes (in animal cells), peroxisomes, and vacuoles (tonoplasts in plant cells). Other cellular structures include ribosomes, the cytoskeleton (microtubules, microfilaments, and intermediate filaments), centrosomes (with centrioles in animal cells), mitotic spindles, cilia, and flagella. Cells arise from progenitor or stem cells and become specialized for one or more distinct functions such as contraction, nerve conduction, secretion, absorption, or protection in multicellular organisms. This process of cell specialization is known as cell differentiation. Structural or morphological modifications during differentiation are accompanied by
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2 biochemical changes. For example, formation of red blood cells in human requires the differentiating cells to lose their nuclei and to make specialized proteins for oxygen transport. See Appendix A to review characteristic structures found in animal, plant and bacterial cells. Use of microscopy to study cellular structure The structures of interest to cell biologists range widely in size. For example, the diameter of a mitochondrion is about 0.5 μm, the length of many bacteria roughly 1 μm, and the diameters of most mammalian cells in the range of 5 to 50 μm. Because cells are generally too small to be seen by the unaided human eye, we rely largely on microscopes to see detailed information concerning cell structure. All microscopes are characterized by limits of
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1 PROTO - Biol 2030U Fall 2010 Experiment # 1: Cellular...

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