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chap6studyguide - Chapter 6 A Tour of the Cell Study Guide...

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Chapter 6 A Tour of the Cell Study Guide Overview: The Importance of Cells All organisms are made of cells. ° Many organisms are single-celled. ° Even in multicellular organisms, the cell is the basic unit of structure and function. The cell is the simplest collection of matter that can live. All cells are related by their descent from earlier cells. Cell biologists can isolate organelles to study their functions. The goal of cell fractionation is to separate the major organelles of the cells so their individual functions can be studied. This process is driven by an ultracentrifuge, a machine that can spin at up to 130,000 revolutions per minute and apply forces of more than 1 million times gravity (1,000,000 g). Fractionation begins with homogenization, gently disrupting the cell. The homogenate is spun in a centrifuge to separate heavier pieces into the pellet while lighter particles remain in the supernatant. ° As the process is repeated at higher speeds and for longer durations, smaller and smaller organelles can be collected in subsequent pellets. Cell fractionation prepares isolates of specific cell components. This enables the functions of these organelles to be determined, especially by the reactions or processes catalyzed by their proteins. Eukaryotic cells have internal membranes that compartmentalize their functions Prokaryotic and eukaryotic cells differ in size and complexity. All cells are surrounded by a plasma membrane. The semifluid substance within the membrane is the cytosol, containing the organelles. All cells contain chromosomes that have genes in the form of DNA. All cells also have ribosomes, tiny organelles that make proteins using the instructions contained in genes. A major difference between prokaryotic and eukaryotic cells is the location of chromosomes. In a eukaryotic cell, chromosomes are contained in a membrane-enclosed organelle, the
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nucleus. In a prokaryotic cell, the DNA is concentrated in the nucleoid without a membrane separating it from the rest of the cell. In eukaryote cells, the chromosomes are contained within a membranous nuclear envelope. The region between the nucleus and the plasma membrane is the cytoplasm. ° All the material within the plasma membrane of a prokaryotic cell is cytoplasm. Within the cytoplasm of a eukaryotic cell are a variety of membrane-bound organelles of specialized form and function. ° These membrane-bound organelles are absent in prokaryotes. Eukaryotic cells are generally much bigger than prokaryotic cells. The logistics of carrying out metabolism set limits on cell size. ° At the lower limit, the smallest bacteria, mycoplasmas, are between 0.1 to 1.0 micron. ° Most bacteria are 1–10 microns in diameter.
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chap6studyguide - Chapter 6 A Tour of the Cell Study Guide...

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