Cells 1

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  • Cells
    • Cytoskeleton -  network of fibres made of protein
      • These fibres keep the cell's shape stable by providing n internal framework
      • Actin filaments - are like fibres found in muscle cells. They are able to move against each other.
        • Cause the movement seen in some white blood cells. Also move organelles around the cell
      • Microtubules - other fibres made of a protein called tubulin
        • Cylinders are 25nm in diameter.
        • May be used to move microorganims through a liquid, or to waft a liquid past the cell
        • Proteins present on the microtubles move organelles and other cell contents along the fibres.
          • How chromosomes are moved during mitosis
          • How vesicles move from the endoplasmic reticulum to the Golgi apparatus
          • These proteins are known as microtuble motors - ATP to drive these movements
    • Flagella and cilia
      • Flagella also known as undulipodia
      • Structurally the same - hair-like extensions that stick out from the surface of cells
        • Each one is made up of a cylinder that contains 9 microtubles arranged in a circle with 2 mircrotubles in the centre
      • Flagella forms the tail of the sperm cell
      • Cilia move substances such as mucus across the surface of the cell
      • Can move because the microtubules use ATP
      • Flagella usually occur in ones and twos on a cell
      • Cilia often occur in large numbers on a cell
    • Vesicles and Vacuoles
      • Vesicles are  membrane bound sacs found in cells. Used to carry many different substances around the cell.
      • In plant cells, the large cell vaculole maintains cell stability. Is filled with water and solutes, so it pushes the cytoplasm against the cell wall, making the cell turgid
    • Plant cell walls-  outside of the plant cell plasma membranes. Made of cellulose -  forms a sieve like network of strands that makes the wall strong.
    • Division of Labour
      • Some of the cells within some organisms produce hormones
      • The instructions to make the hormone are in the DNA in the nucleus
        • The specific instruction to make a hormone is called a gene
          • The nucleus copies the instructions in the DNA into a molecule called mRNA
            • The mRNA molecule leaves the nucleus through a nuclear pore and attaches to a ribosome
              • The ribosome is attached to rough ER
              • The ribosome reads the instructions and uses the codes to assemble the hormone
                • The assembled protein inside the rough ER is pinched off in a vesicle and transported to Golgi appartus
                  • The Golgi apparatus packages the protein and may also modify it so that it is ready for release. The protein is now packaged into a vesicle and moved to the cell surface membrane, where it is secreted outside
    • Eukaryotes
      • The cells described so far all contain organelles, some of which are bound by membrane.
        • This gives these cells a complicated internal structure, where each organelle performs a specific role, these are called eukaryotic cell
          • Have a true nuclueus
    • Prokaryotes
      • Features
        • Only one membrane - no membrane bound organelles
        • Surrounded by a cell wall
          • Outside cell wall there is often a slippery protective layer called the capsule
        • Contain small ribosomes
        • Single loop of DNA
          • DNA not surrounded by a membrane


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