Organelles - structure and function

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  • Organelles - structure and function
    • Golgi apparatus
      • Stack of membrane-bound, flattened sacs.
      • Receives proteins from the ER and modifies them. May add sugar molecules to them. Then packages the proteins into vesicles. Some proteins may go to the cell surface for secretion.
    • Ribosomes
      • Consists of two subunits. Some are free in the cytoplasm and some are attached to the rough ER.
      • Site of protein synthesis in the cell. Act as an assembly line, where mRNA from the nucleus is used to assemble proteins from amino acids.
    • Endoplasmic reticulum
      • Flattened membrane-bound sacs called cisternae Continuous with the outer nuclear membrane. Rough ER contains ribosomes, smooth ER doesn't.
      • Rough ER transports proteins that were made on attached ribosomes. Some of these proteins may be secreted from the cell. Some will be placed on the cell surface membrane. Smooth ER is involved in making the lipids that the cells need.
    • Centrioles
      • Small tubes of protein fibres.
      • Take part in cell division. Form fibres known as spindle, which move chromosomes during nuclear division.
    • Mitochondria
      • Spherical or sausage shaped. Two membranes separated by a fluid-filled space. Inner membrane is highly folded to form cristae. Central part of the mitochondrion is the matrix.
      • Produces most of the ATP during respiration.
    • Lysosomes
      • Spherical sacs surronded by a single membrane.
      • Contain powerful digestive enzymes. Role is to break down certain materials.
    • Nucleus
      • Surrounded by a nuclear envelope and when darkened, shows chromatin. Nuclear pores (holes) go through the envelope. The nucleolus is inside the nucleus.
      • Houses nearly all of the cells genetic material. Chromatin consists of DNA and protein. Has the instructions for making proteins. When cells divide, chromatin turns into chromosomes. Nucleolus makes RNA and ribosomes. These pass into the cytoplasm where proteins are assembled.
    • Chloroplast
      • Only found in plant cells and some protoctists. Have two membranes. Inner membrane is continuous, with a network of flattened membranes called thylakoids. A stack of thylakoids is called a granium.
      • Site of photosynthesis in plant cells. Light energy is used to drive the reactions of photosynthesis, in which carbohydrate molecules are made from carbon dioxide and water.


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