Cell Structure
- Created by: Dani_Gregs7
- Created on: 24-06-17 23:17
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CELL FRACTIONATION:
- 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:
- Cold - to reduce enzyme activity that might break down the organelles.
- Is of the same water potential as the tissue - to prevent organelles bursting or shrinking as a result of osmotic gain or loss of water.
- Buffered - so that the pH does not fluctuate. Any change in pH could alter the structure of the organelles or affect the functioning of enzymes.
- There are 2 stages to cell fractionation:
- Homogenisation:
- Cells are broken up by a homogeniser (blender).
- This releases the organelles from the cell.
- The resultant fluid, known as homogenate, is then filtered to remove any complete cells and large pieces of debris.
- Ultracentrifugation:
- The process by which the fragments in the filtered homogenate are separated in a centrifuge.
- This spins tubs of homogenate at very high speed in order to create a centrifugal force.
- For animal cells, the process is:
- 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 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 each increase in speed, the next heaviest organelle is sedimented and separated out.
- Homogenisation:
EUKARYOTIC CELL STRUCTURE:
- THE NUCLEUS:
- Contains the organism's hereditary material and controls the cell's activities.
- Usually spherical and between 10 and 20 micrometres in diameter, the nucleus has a number of parts:
- The nuclear envelope:
- A double membrane that surrounds the nucleus.
- Its outer membrane is continuous with the endoplasmic reticulum of the cell and often has ribosomes on its surface.
- It controls the entry and exit of materials in and out of the nucleus and contains the reactions taking place within it.
- Nuclear pores:
- Allow the passage of large molecules, such as mRNA, out of the nucleus.
- There are typically around 3000 pores in each nucleus, each 40-100nm in diameter.
- Nucleoplasm:
- The granular, jelly-like material that makes up the bulk of the nucleus.
- Chromosomes:
- Consist of protein-bound, linear DNA.
- The nucleolus:
- A small spherial region within the nucleoplasm.
- It manufactures rRNA and assembles the ribosomes.
- There may be more than 1 nucleolus in a nucleus.
- The nuclear envelope:
- Functions:
- Act as the control centre of the cell through the production of mRNA and tRNA and hence protein synthesis.
- Retain the genetic material of the cell in the form of DNA and chromosomes.
- Manufacture rRNA and ribosomes.
- THE MITOCHONDRION:
- Usually rod-shaped and 1-10 micrometres in length.
- Made up…
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