Organelles and compartmentalisation

• Advantages of compartmentalisation in the cytoplasm of cells

  Specialised enzymes and substrates are far more concentrated than if they were to be spread across the cytoplasm

  Dangerous substances (such as those within lysosomes) may be kept inside a membrane to reduce harm to the cell

  Conditions such as pH for a particular process are maintained in one organelle, which may be different from the conditions needed elsewhere in the cell.

  Organelles and their contents are able to move

  Larger area of membrane available for processes that happen within or across membranes.
• Advantages of the separation of the nucleus and the cytoplasm in eukaryotes

  In eukaryotic cells, translation cannot begin until messenger RNA (mRNA) has passed out of the pores in the nuclear membrane, allowing it to be modified after transcription, before translation. This is known as post-transcriptional modification
• Differential conjugation


  Separating cells into types of organelle is known as cell fractionation. This is done through mixing the cells with an ice cold extraction buffer, which slows down degeneration and prevents osmosis and pH differences. This mixture is blitzed to burst open the cells and release the organelles. The resulting homogenate ( suspension of cell fragments and cell constituents obtained when tissue is homogenized (made uniform or similar)) is filtered to remove structures larger than organelles. Then it is centrifuged (separated), and as organelles are denser than the extraction buffer, they sediment to the bottom of the centrifuge tube, forming a 'pellet'. The remaining liquid, which is known as a supernatant, is discarded.

  The pellet is then mixed with another solution, which resuspends them. This new mixture is centrifuged again, speed and duration selected so that the desired organelles will seperate, known as differential centrifugation. the larger organelles will sink to the bottom of the tube faster than the smaller organelles. The density of the liquid may be varied to seperate organelles of different denisties. This process has been made possible by new technological advancements such as ultracentrifuges
• Organelles definition


  Organelles are discrete subunits of cells that are adapted to perform specific functions.
• NOT organelles


  Cell wall, Cytoskeleton, Cytoplasm
• Organelles


  Ribosomes, Centrioles, Microtubules, Nuclei, Vesicles, Vacuoles, rER, smooth ER, Golgi apparatus, Lysosomes, Mitochondria, Chloroplasts, Amyloplasts