Cell Ultrastructure and Function - PDF

Cell Ultrastructure and Function The contents of the cell may be divided into two broad areas : the Nucleus and the Cytoplasm Collectively they form the protoplasm.  Cytoplasm consists of an aqueous background material which contains a...

Cell Ultrastructure and Function The contents of the cell may be divided into two broad areas : the Nucleus and the Cytoplasm Collectively they form the protoplasm.  Cytoplasm consists of an aqueous background material which contains a variety of organelles and inclusions. The aqueous component of the cytoplasm is known as the cytosol, and consists of about 90% water.  Looks transparent and structureless, but contains complex networks of microfilaments, forming the cytoskeleton. Contains the contractile protein actin, and is involved in endocytosis / exocytosis and motility --- cytoplasmic streaming. microtubuletransport.swf  It is also used for: Support and shape for cell. Organises and moves organelles Forms the spindle during cell division. Cytosol also contains a wide range of biochemicals, such as salts, amino acids, glucose, etc in true solution.  Larger molecules such as proteins in colloidal solution: Sol (non-viscous), Gel (viscous). The cytoplasm may also act as a site for metabolic pathways eg. Glycolysis.  Membranes.. see previous notes….. Endoplasmic Reticulum (ER) This is a complex system of flattened membrane bound vesicles (cisternae). These are arranged in stacks or concentric patterns around other organelles such as mitochondria, or in a tubular form. There are two distinct types of E.R.  Rough E.R., which has ribosomes attached to the outer surface of the cisternal membrane, and is concerned with the synthesis and transport of proteins, and joins with the nuclear envelope.  Small vesicles containing the newly synthesised proteins are pinched off at the ends, and either fuse with the Golgi apparatus, or directly to the cell membrane. Smooth E.R.,  Smooth E.R., has No ribosomes associated with the cisternal membrane. One of its chief functions is the transport and synthesis of lipids, including steroids. Also involved in detoxification processes in the liver, and as a site for calcium storage in skeletal muscle cells. Ribosomes  These are very small organelles; 20nm in diameter. Function as sites for protein synthesis. Found in association with Rough E.R., or alone within the cytoplasm. also within other organelles: mitochondria and chloroplasts Composed of 2 subunits, which both contain RNA and Protein.  This type of RNA is termed ribosomal RNA or rRNA. During the process of protein synthesis, ribosomes may associate together, to form chains, known as polyribosomes, or polysomes. These may be seen as whorled patterns on the E.R. Golgi Apparatus First described by Camillo Golgi in 1898, using special staining techniques. Its structure was not revealed until the use of the E.M., and would seem to be a specialised part of the smooth E.R. It consists of stacks of between 3 to 8 flattened plate like cisternae, called saccules. These in turn may be arranged into a number of separate stacks known as dictyosomes, esp. in plants. On the outer edge of the concave stack, new cisternae are being formed, by the fusion of vesicles, normally derived from E.R. At the inner maturing face of the stack, the cisternae bud into new vesicles, which then discharge their contents by fusion with plasma membranes.  The function of the Golgi apparatus is to transport and chemically modify the materials contained within it. Proteins, lipids and carbohydrates. Also forms Lysosomes Lysosomes:  Membrane bound vesicles 0.2-0.5 m in diameter Contains digestive enzymes known as lysitic enzymes. Used to destroy old or surplus organelles. Breakdown whole cells and tissues. Used to digest material taken into cells.. linked to phagocytosis. 1o and 2o Lysosomes Peroxisomes … contain catalase, for the decomposition of hydrogen peroxide. Mitochondria: These are small elongated organelles, 2 to 5 m in length found in all eukaryotic cells. Involved with cellular respiration… Aerobic cellular respiration Linked to the metabolic pathways of the cytoplasm Each mitochondrion is bounded by a double membrane system or envelope with a space of around 6 to 10nm between them. The inner membrane is folded inwards to form a number of folds or cristae, which project into a semi-ridged matrix. This inner membrane increases the surface area available for contact with enzymes of the matrix. It is also selectively permeable. The cristae themselves have stalked particles covering their surface and are composed mainly of ATPase.  During aerobic cellular respiration, ATP is produced from ADP and inorganic phosphate ions. This happens through the oxidation of energy rich substrates... pyruvic acid, derived from sugars (such as glucose) by the process of glycolysis in the cytoplasm. Abundent in cells and tissues, that require large amounts of energy, such as the liver and muscles. Both mitochondria and chloroplasts, contain limited amounts of DNA, and thus have a limited capacity for protein synthesis. They also contain ribosomes. Nucleus Heterochromatin and Euchromatin. Microtubules Centrioles Cilia and Flagella  Functions of flagella Locomotion – flagellate protozoans use a flagellum for locomotion Feeding – in sponges, flagella create a flow of water through the organism, and food is removed. Reproduction – sperm of vertebrates are propelled by means of their flagellate tails.  Functions of cilia Locomotion – protozoans such as Paramecium Feeding – filter feeders such as mussels use cilia to create a flow of water. Reproduction – cilia may contribute to the movement of ova down the oviduct in mammals. Gaseous exchange –  Gaseous exchange – used to remove mucus from the respiratory tract. Transport of nutrients – central canal and ventricles of the central nervous system are lined with cilia, which circulate the cerebro-spinal fluid.  Microvilli plus Cell Junctions Chloroplasts Vacuoles Cellulose Cell Wall