Methods of Cell Centrifugation--论文代写范文精选

51Due论文代写网精选essay代写范文：“Methods of Cell Centrifugation” 这篇生物essay代写范文阐述的是关于细胞的离心法细胞器如细胞核、线粒体等,可以从细胞中分离，也就是离心。大多数情况中，干扰最简单的办法就是在低温下O°C和4°C之间,特别是对于保护代谢活动的后续研究。细胞分裂后,颗粒组件彼此分离。离心的方法有两种:差速离心和梯度差速离心法，第一种取决于各个组件之间沉降速度的差异。第二种取决于不同细胞组件之间的密度梯度。离心后,细胞组件有不同的沉积率，细胞的化学成分,如核蛋白质和酶的组织是冻干和悬浮在非水溶剂中。(论文代写)

Cell organelles such as nuclei, mitochondria, etc., can be removed from the cell and separated from each other by centrifugation, which is done in a centrifuge Before centrifugation, cells are first disrupted either by grinding tissue in a mortar or homogenization in ground glass or exposure to sonic vibrations. In most cases, disruption is best done at low temperatures between O°C and 4°C, especially for the preservation of metabolic activity for subsequent study.

After cell disruption, the particulate components are separated from each other by high speed centrifugation.

There are two methods of centrifugation:

(1) differential centrifugation and
(2) gradient differential centrifugation.

1. Differential Centrifugation:

It depends on differences in sedimentation rate among various components. The heavier particles settle first and then there is gradual separation by sedimentation of light particles. For example, centrifugation at a speed 700 times gravity of a tissue homogenate suspended in 0.25M sucrose results in the separation of nuclei.

If the supernatant resulting from this centrifugation is centrifuged at about 5000 to 8500 times gravity, the mitochondria settle out of solution. At still higher speed, other particulate components are separated. For example, microsomal fraction in 0.25M sucrose is obtained by 30 minute centrifugation at 100,000 times gravity.

2. Gradient Differential Centrifugation:

It depends on density gradient among different cellular components. In this case the homogenate is placed in a tube on top of a sucrose column, which is stratified, i.e., sucrose solution progressively increases in density from top to bottom. Upon centrifugation, cellular components having different sedimentation rates appear at different levels according to their size and specific gravity.

For chemical components of cells, specific procedures are followed. For example, retention of nucleoprotein and enzymes of the nucleus, the tissue is freeze-dried (lyophilized) and suspended in a non-aqueous solvent (for nuclei, an ether-chloroform mixture or a benzene-carbon tetrachloride mixture). Cells are disrupted by grinding in a colloid mill or a mortar, and the nuclei are isolated by gradient differential centrifugation.(论文代写)

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