EUKAROTIC ORGANELLES

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  • Eukaryotic Organelles
    • Animal Cell
      • Mitchondria
        • Powerhouse of the cell. Site of aerobic respiration, production of ATP.
        • Double membrane, inner membrane is folded up to form CRISTAE.
        • The number of mitochondria in the cell are relative to the needs of the cell.
        • ENDOSYMBIOTIC THEORY
          • Evidence for endosymbiotic theory is that 70S ribosomes are reproduced in the mitochondria and chloroplasts independantly when cell divides.
            • 70S Ribosomes are found in mitochondria and chloroplasts of plant cells and in prokaryotes. Made up of 50S and 30S subunits with RNA:Protein ratio of 2:1
      • Cell membrane
        • Controls what enters and leaves the cell. Made of phospholipid bilayer, has channel and carrier proteins which allow and permits substances to move in and out of cell.
      • Nucleus
        • Contains the genetic information for the production of proteins. Site of transcription in protein synthesis.
        • The Nucleus is the largest organelle in the cell. Double nuclear membrane/ nuclear envelope that contains pores. Inside nucelar envelope are nucleic acids and proteins.
        • When the cell is not actively dividing, the DNA is bonded to chromatin - seen as granules. Also there is at least one NUCLEOLUS - an extra dense area of almost pure DNA and protein.
      • Ribosomes
        • Some are attached to the RER and are the site of translation in protein synthesis
          • 80S and 70S Ribosomes.
            • 80S is made up of 40S and 60S subunits and has a RNA:protein ratio of 1:1.
            • 70S Ribosomes are found in mitochondria and chloroplasts of plant cells and in prokaryotes. Made up of 50S and 30S subunits with RNA:Protein ratio of 2:1
      • Endoplasmic Reticulum
        • RER - has ribosomes and therefore isolates and transports the proteins made in the ribosomes - has a large SA - more space for synthesis and storage.
        • SER - involved in the sythesis and transport of lipids and steroids.           E.g. lots of SER in testes whihc makes steroid hormone testosterone,   The liver has lots as well as it metabolises cholesterol.
      • Cytoskeleton
        • Made up of centrioles and microtubules. Many microfilamentare related to ACTIN and MYOSIN (contractile proteins in muscle) so the cytoskeleton is closely linked with cell movements and transport.
        • Each centriole is made up of a bundle of 9 tubules. They are involved in cell division - centrioles pull apart to form spindle fibres which are involved in the movement of chromosomes
        • Dynamic 3D web-like structure. Microfilament are protein fibres, and microtubules are tiny protein tubes. Microtubules consist of TUBULIN.
      • Golgi Apparatus
        • Stacks of parallel, flattened membrane called CISTERNAE - formed by vesicles from the ER fusing together.
        • Proteins are brought to the Golgi in VESICLES which have pinched off form RER. The vesicles fuse with the membrane sacks.
        • The Golgi modifies proteins - adds carbs to form glycoproteins such as mucus.
          • LYSOSOME
            • Some proteins in Golgi are digestive enzymes enclosed in vesicles - forming lysosomes.
            • Fuse witht the cell membrane to release extrecellular digestive enzymes.
              • Dark spherical bodies - help in apoptosis of worn out cells. Help to destroy pathogens.
                • APOPTOSIS  - Destroys cells whose DNA replication is not functioning well.                - Cancer - cells fail to die by apoptosis     - Excessive apoptosis is bad - after heart attack, in autoimmune diseases , death of T killer cells in HIV/AIDS.
            • Dark spherical bodies - help in apoptosis of worn out cells. Help to destroy pathogens.
              • APOPTOSIS  - Destroys cells whose DNA replication is not functioning well.                - Cancer - cells fail to die by apoptosis     - Excessive apoptosis is bad - after heart attack, in autoimmune diseases , death of T killer cells in HIV/AIDS.
          • Enzymes and proteins have been radioactively labelled to see what happens in the Golgi. The inner areas of the Golgi are very rich in enzymes which modify proteins and the outer areas are rick in already completed proteins.
      • Vacuole
        • Not a permanent feature in animal cells. Simple animals make food vacuoles around thier prey. White blood cells form vacuoles around engulfed pathogens.
        • Contractile vacuoles - in simple aquatic organisms - allow water content of cytoplasm to be controlled.
    • Plant cell
      • Chloroplasts
        • Contains chlorophyll which captures sunlight - photosynthesis.
        • All plants have genetic info to make chloroplasts but majority do not have it.
      • Cell Wall
        • GIves plant cells strength and support
        • Made up of insoluble cellulose which is freely permeable to substances. But once it becomes impregnated with SUBERIN or LIGNIN, it is impermeable to water and other substances.
        • MIDDLE LAMELLA - first layer to form. Made of PECTIN which has negative -COOH groups wihc combine with Ca2+ ions to make CALCIUM PECTATE.
          • The cellulose microfibriles are on either side of middle lamella and this begins very flexible because microfibrils are all in same direction. - THIS PRIMARY CELL WALL.
          • SECONDARY CELL WALL - microfibrils laid densely at different angles - Hemicelluloseand lignin in woody plants increases rigidity of the structure.
      • Vacuole
        • Can occupy 80% of the cell's volume. Filled with cell sap - solution of nutrients and H2O - allows water to move in to cell by osmosis
        • Keeps the cytoplasm pressed against the cell wall - keeps it upright. Maintains a high pressure.
        • Stores pigments, and proteins in seeds and fruits. Sometimes stores lytic enzymes. Stores waste products and foxgloves stores chemical which works on the heart.
      • Tonoplast
        • Surrounds a vacuole - has many protein systems to control the water potential of the cell.
      • Plasmodesmata
        • Special cytoplasmic bridges
        • Signalling chemicals can be passed on through the symplast pathway.
        • EVIDENCE - grafted tissue will only start healthy cell division once plasmodesmata is established between host tissue and graft tissue.
      • Amylose
        • Develop form leucoplasts - they are colourless and store starch which can be converted to glucose to provide energy when the cell needs it. Found in large numbers in plants that sores starch a lot - potato tubers.

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