Angela Fishwick |
sample is placed in an ultracentrifuge and spun in low speed - nuclei settle out, forming a pellet The supernatant (suspension containing remaining organelles) is spun at a higher speed - chloroplasts settle out The supernatant is spun at a higher speed still - mitochondria and lysosomes settle out The supernatant is spun at an even higher speed - ribosomes, membranes settle out The ribosomes, membranes and Golgi complexes can be separated by another technique called density gradient centrifugation. Ultracentrifugations Main articles: Differential centrifugation, Isopycnic centrifugation, and ultracentrifugation Ultracentrifugation makes use of high centrifugal force for studying properties of biological particles. Compared to microcentrifuges or high-speed centrifuges, ultracentrifuges can isolate much smaller particles, including ribosomes, proteins, and viruses. Ultracentrifuges can also be used in the study of membrane fractionation. This occurs because ultracentrifuges can reach maximum angular velocities in excess of 70,000 rpm. Additionally, while microcentrifuges and supercentrifuges separate particles in batches (limited volumes of samples must be handled manually in test tubes or bottles), ultracentrifuges can separate molecules in batch or continuous flow systems. In addition to purification, analytical ultracentrifugation (AUC) can be used for determination of the properties of macromolecules such as shape, mass, composition, and conformation. Samples are centrifuged with a high-density solution such as sucrose, caesium chloride, or iodixanol. The high-density solution may be at a uniform concentration throughout the test tube ("cushion") or a varying concentration ("gradient"). Molecular properties can be modeled through sedimentation velocity analysis or sedimentation equilibrium analysis. During the run, the particle or molecules will migrate through the test tube at different speeds depending on their physical properties and the properties of the solution, and eventually form a pellet at the bottom of the tube, or bands at various heights. Density Gradient Centrifugation Density gradient centrifugation is considered one of the more efficient methods of separating suspended particles. Density gradient centrifugation can be used both as a separation technique and as a method of measuring the densities of particles or molecules in a mixture.[7] A tube, after being centrifuged by this method, has particles in order of density based on height. The object or particle of interest will reside in the position within the tube corresponding to its density.[8]
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Shauna Grant The Last Porn Queen |
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