Ultracentrifugation A summary of the main points of ultracentrifugation. 3.0 / 5 based on 5 ratings ? BiologyASAQA Created by: Marianne BradleyCreated on: 26-09-10 14:06 Process Homogenate filtered Low speed: remove unbroken cells 600g: nuclei supernatant spun 15000g: mitochondria, chloroplasts, lyosomes and peroxisomes 100,000g: plasma membrane, endoplasmic reticulum, large polyribosomes. Additional centrifugation: ribosomes, enzyme complex 300,000g: Only the cytosol remains after centrifugation This process means that at each stage of centrifugation, the next heaviest organelle is separated out. 1 of 3 Definitions Cellular homogenate is the liquid that contains the biological material. It must first be filtered to remove clumps. The supernatant is the undeposited material left over after centrifugation. Cytosol is the soluble aqueous portion of the cytoplasm. 2 of 3 Information about the process Vacuum conditions are used because this reduces heating caused by friction between air and the spinning rotor. Tissue is placed into a cold isotonic buffered solution before cell fractionation occurs. It is cold because this reduces enzyme activity which could break down organelles. It is isotonic to prevent organelles bursting or shrinking as a result of osmotic water gain or loss. It is buffered so that a constant pH is maintained. 3 of 3
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