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Methods of studying cells - Coggle Diagram
Methods of studying cells
Microscopy
Microscopes are instruments that produce a magnified image of an object. A simple convex glass lens can act as a magnifying glass but such lenses work more effectively if they are used in pairs in a compound light microscope.
The relatively long wavelength of light rays means that a light microscope can only distinguish between two objects if they are 0.2um, or further, apart.
This limitation can be overcome by using beams of electrons rather than beams of light. With their shorter wavelengths, the beam of electrons in the electron microscope can distinguish between two objects only 0.1nm apart.
Magnification
The material that is put under a microscope is referred to as the object. The appearance of this material when viewed under the microscope is referred to as the image.
The magnification of an object is how many times bigger the image is when compared to the object
Magnification = size of image over size of real object
Size of real object = size of image over magnification
Size of image = magnification x size of real object
Resolution
The resolution of a microscope is the minimum distance apart that two objects can be in order for them to appear as separate items.
Whatever, the type of microscope, the resolving power depends on the wavelength or form of radiation used.
Increasing the magnification increases the size of an image, but does not always increase the resolution.
Every microscope has a limit of resolution. Up to this point increasing the magnification will reveal more detail but beyond this point increasing the magnification will not do this. The object, while appearing larger, will just be more blurred.
Cell fractionation
In order to study the structure and function of the various organelles that make up cells, it is necessary to obtain large numbers of isolated organelles.
Cell fractionation is the process where cells are broken up and the different organelles they contain are separated out.
Before cell fractionation can begin, the tissue is placed in a cold, buffered solution of the same water potential as the tissue. The solution is:
Also known as a cold, isotonic solution
Isotonic - is of the same water potential to prevent organelles bursting or shrinking as a result of osmotic gain or loss of water.
Cold - to reduce enzyme activity that might break down the organelles
Buffered - so that the pH does not fluctuate. Any change in pH could alter the structure of the organelles or affects the functioning of enzymes.
There are two stages of cell fractionation
Homogenation
Cells are broken up by the homogeniser (blender). This releases the organelles from the cell. The resultant fluid, known as homogenate, is the filtered to to remove any complete cells and large pieces of debris.
Ultracentrifugation
Ultracentrifugation is the process by which the fragments in the filtered homogenate are separated in a machine called a centrifuge. This spins tubes of homogenate at very high speed in order to create a centrifugal force. For animal cells, the process is as follows:
The tube of filtrate is placed in the centrifuge and spun at a slow speed.
The heaviest organelles, the nuclei, are forced to the bottom a=of the tube, where they form a thin sediment or pellet.
The fluid at the top of the tube (supernatant) is removed, leaving just the sediment of nuclei.
The supernatant is transferred to another tube and spun in the centrifuge at a faster speed than before.
The next heaviest organelles, the mitochondria, are forced to the bottom of the tube.
The process is continued in this way so that, at eeach increase in speed, the next heaviest organelle is sedimented and separated out.