BIOMEMBRANES

BIOMEMBRANES

1. CYTOSKELETON

   • Microfilaments
     • 8–9 nm in diameter
     • made of monomeric actin subunits
     • Membrane–microfilament binding proteins tack the actin cytoskeleton framework to
       • membrane
   • Intermediate filaments
     • 10-nm-diameter
     • made of lamin subunits and other tissue- specific proteins
     • adapter proteins attach them to
       • desmosomes and hemidesmosomes
   • Microtubules
     • 24 nm in diameter
     • they are hollow tubelike structures
     • made of alpha and beta tubulin subunits
     • radiate out
       • single microtubule-organizing center
   • funcitions in animal and plan cells
     • contributes to cell movement
     • cell polarity
     • It organizes the contents of the cell
     • Support for nuclear membrane
   • functions in bacteria
     • controls cell length, width,andthe site of cell division

2. ORGANELLES OF THE EUKARYOTIC CELL

   • TWO BILAYER MEMBRANES
     • THE NUCLEUS
       • Houses the genome of the cell
       • numerous nuclear pores: materials pass between the nucleus and the cytosol
     • MITOCHONDRIA
       • has highly permeable outer membrane protein-enriched inner membrane
       • ATP synthesis : Enzymes in the inner mitochondrial membrane and central matrix
     • CHLOROPLASTS
       • thylakoid membranes in their interiors: contain the pigments and enzymes that absorb light— ATP syntesis
   • A SINGLE MEMBRANE
     • The Golgi Complex
       • processes and sorts secreted and membrane Proteins -it has three regions: the cis, the medial, and the trans.
     • Plant Vacuoles
       • Store Small water, ions, and nutrients -contain degradative enzymes and -has an acidic pH
     • The Rough Endoplasmic Reticulum
       • synthesizes
         • membrane and organelle proteins
         • all proteins to be secreted from the cell
     • ENDOSOMES
       • Take up plasma-membrane proteins and soluble materials from the extracellular medium and recycles or degrades them.
     • LYSOSOMES
       • Contain hydrolases - degrade unneeded cellular components and some ingested materials
     • Peroxisomes
       • Contain enzymes that oxidize various organic compounds without the production of ATP
     • The Smooth Endoplasmic Reticulum
       • synthesizes fatty acids and phospholipids
       • detoxifies of hydrophobic chemical

3. Purification of cells and their parts:

   • Studies on cell structure require particular type or subcellular organelle from a cell
     • Tissues contain mixture of cell types
     • Cells filled with different organelles
   • Techniques for separating different cell types and organelles
     • Flow Cytometry
       • Separates Different Cell Types
       • Can identify different cells on the basis of the light
         • These can be by
           • Scatter
           • Fluorescence that they emit
             • Fluorescence-activates cell sorter (FACTS)
               • Separating different types of cells
     • Disruption of Cells
       • Releases Their Organelles and Other Contents by
         • Vigorous homogenization
         • Other techniques
         • Sonication
       • Swelling of cells
         • Hypotonic solution
           • Weakens the plasma membrane
             • Easier rupture
     • Centrifugation
       • Yields fractions
         • Of: partly purified organelles
           • Differ in
             • mass
             • density
       • Can Separate Many Types of Organelles
     • proteins
       • Transmembrane proteins
         • Selectively solubilized
           • Purified with nonionic detergents
     • Organelle Specific Antibodies
       • Using antibodies against organelle specific membrane proteins
         • Useful in preparing
           • Highly Purified Organelles
           • Vesicles of similar
             • sizes
             • densities