Cells/Organelles at Work

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  • Cells/Organelles at work
    • Proteinsynthesis
      • instructions to make a hormone are in the DNA in the nucleus
        • the specific instruction in the DNA is known as the gene for that hormone, a gene is on a chromosome
        • the nucleus copies the instructions in the DNA into mRNA
          • the mRNA leaves the nucleus through a pore and attaches to a ribosome (that is attached to REM)
            • the ribosome reads the instructions and uses the codes to assemble the hormone
              • the protein is pinched off in a vesicle and transported to the golgi body
                • the golgi body  packages the protein and may modify it so it is ready for release. Protein is packaged at moved to the cell surface membrane, where it is secreted outside
        • Happens in ribosomes either free or on the rough endoplasmic reticulum
    • Prokaryotic  cells
      • Have NO nucleus or mitochondria
      • one membrane (cell surface), surrounded by a cell wall (made of peptidogltycan)
      • have smaller ribosomes than Eukaryotes
      • single loop of DNA in the cytoplasm, circular and sometimes very small loops of DNA called plasmids
      • ATP production takes place in specialized in folded regions of the cell surface called mesosomes
      • some have flagella, that are different internally to those in eukaryotic undulipodia
      • some cause diseases, and can be resistant to antibiotics, this is due to the resistance being coded on plasmid DNA
      • some are used in food(cheese, yoghurt), in mammals intestines to digest, skin, sewage treatment
    • Communication and Cell signalling
      • cell signalling - cells communicate by signals, many molecules act as these signals
        • signal molecules fit into receptor molecules on cell surface membranes - their shapes are complementry
      • cells must be able to detect nutrient molecules, various internal and external signals used to co-ordinate and carry out processes, carry out functions in response to signals
      • Hormone receptors - hormones are chemical messengers produced in specific tissues and released into the organism
        • any cell with a receptor for the hormone molecules is called a target cell
        • Insulin is released from special cells in islets of Langerhans in the pancreas in response to increased blood sugar levels
          • it is a protein molecule that attaches to the insulin receptors on the plasma membranes, triggering internal responses in muscle cells that lead to more glucose channels being present in the plasma membrane - allowing the cell to take up more glucose from the blood
      • medicinal drugs can interfere with receptors - e.g. beta blockers
      • Viruses enter cells by binding with receptors on the cell's plasma membrane that normally bind with signalling molecules
        • Viruses then use the cells DNA to reproduce, so that the cell can't use it and it is destroyed
      • poisons also bind with receptors, can stop the muscle fibres from working properly


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