Eukaryotic cell structure

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  • Created by: Nelle101
  • Created on: 28-11-15 11:44
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  • Eukaryotic Cell Structure
    • Eukaryotes
      • Multicellular organisms such as animals, plants and fungi
    • Complicated internal structure containing: a membrane-bound nucleus (nucleoplasm) and cytoplasm, which contains many membrane-bound cellular components
    • Organelles
      • Nucleus
        • Contains  coded genetic information in the form of DNA molecules. DNA directs the synthesis of all proteins required by the cell (although protein synthesis occurs outside of the nucleus at ribosomes).In this way, the DNA controls the metabolic activities of the cell, as many of these proteins are the enzymes necessary for metabolism to take place.
          • DNA itself is too large to leave the nucleus to the site of protein synthesis in the cell cytoplasm. Instead, it's transcribed into smaller RNA molecules, which are exported ia the nuclear pore.
            • The nuclear envelope contains nuclear pores that allow molecules to move into and out of the nucleus.
        • DNA
          • Contained within a double membrane (nuclear envelope) to protect it from damage in the cytoplasm.
          • DNA associates with proteins called histones to form a complex called chromatin. Chromatin coils and condenses to form structures known as chromosomes. These only become visible when cells are preparing to divide.
        • The nuclear envelope contains nuclear pores that allow molecules to move into and out of the nucleus.
      • Nucleolus
        • An area  within the nucleus that's responsible for producing ribosomes. It's composed of proteins and RNA. RNA's used  to produce ribosomal RNA (rRNA) which is then combined with proteins to form the ribosomes necessary for protein synthesis.
      • Mitochondria
        • Site of the final stages of cellular respiration, where the energy stored in the bonds of complex , organic molecules is made available for the the cell to use by the production of the molecule ATP.
        • The number of mitochondria in a  cell is generally a reflection of the amount of energy it uses.
        • Have a double membrane.The inner membrane is highly folded to form structures called cristae and the fluid interior is called the matrix. The membrane forming the crust contains the enzymes used in aerobic respiration
        • Mitochondria contain a small amount called mitochondrial (mt) DNA
        • Mitochondria can produce their own enzymes and reproduce themselves
      • Vesicles and Lysosomes
        • Vesicles are membranous sacs. They consist of a single membrane with fluid inside. They're used to transport materials inside the cell.
        • Lysosomes are specialised forms of vesicles that contain hydrolytic enzymes. They're responsible for breaking down waste waste material in cells, including old organelles.They play an important role in programmed cell death (apposite) and the immune system as they're responsible for breaking down pathogens ingested by phagocytic cells.
      • Centrioles
        • A component of the cytoskeleton present in most eukaryotic cells except for flowering plants and most fungi. They're composed of microtubules. Two associated centrioles form the centrism, which is involved in the assembly and organisation of the spindle fibres during cell division.
      • Ribosomes
        • Can be free floating in the cytoplasm or attached to EM forming REM (mitochondria and chloroplasts also contain ribosomes). They're not surroundedby a membrane.They're constructed of RNA molecules made in the nucleolus of the cell. They're the site of protein synthesis.
      • Golgi apparatus
        • Similar in structure to the SEM. Compact structure formed of cistern and doesn't contain ribosomes. It modified proteins and packages them into vesicles. These may be secretory if the proteins are destined to leave the cell, or lysosomes, which stay in the cell.
    • Organelles
      • Cytoskeleton (has 3 components)
        • Its present throughtoutthe cytoplasm of all eukaryotic cells Its a network of fibres necessary for the shape and stability of a cell. Organelles are held in place by it and it controls cell movement and the movement of organelles within cells.
        • Microfilaments
          • Contractile fibres formed from the protein actin. These are responsible for cell movement and also cell contraction during cytokinesis (the process in which the cytoplsm of a single eukaryotic cell is divided to form two daughter cells).
        • Microtubules
          • Globular tubulin proteins polymerise to form tubes that are used to form a scaffold like structure that determines the shape of a cell. They also act as tracks for the movement if organelles, including vesicles, around the cell. Spindle fibres are composed of microtubules.
        • Intermediate fibres
          • These fibres give mechanical strength to cells and help maintain their integrity
      • Flagella (whip-like)  and Cilia (hair-like)
        • Flagella are longer than cilia but cilia are usually present in greater numbers.
        • Flagella are mainly used to enable cells motility. In some cells they're used as a sensory organelle to detect chemical changes in the cell's environment
        • Cilis can be mobile or stationary. Stationary ones are present on the surface of many cells and have an important function in sensory organs e.g. the nose. Mobile cilia beat in a rhythmic manner, creating a current, and cause fluids or objects adjacent to the cell to move. E.g. in the trachea they move mucus away fro the lungs (helping to keep the air passages clean) . In fallopian tubes they move egg cells from the ovary to the uterus.
          • Each cilium contains two central microtubules (black circles) surrounded by nine pairs of microtubulesarranged like a wheel. This is known as  the 9+2 arrangement. Pairs of parallel microtubules slide over  each other causing the cilia to move in a beating motion.
      • Endoplasmic reticulum
        • A network of membranes enclosing flattened sacs called cisternae. Its connected to the outer membrane of the nucleus.
        • RER
          • Has ribosomes bound to the surface and is responsible for the synthesis and transport of proteins.
          • Secretory cells, which release hormones or enzymes, have more RER than cells that don't release proteins.
        • SER
          • Responsible for lipid and carbohydrate synthesis and storage.


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