L3 Biological Membranes

Objectives

  1. Describe the function and structure of biological membranes.

  2. Discuss the components of cell membranes (phospholipids, glycolipids, proteins )

  3. Describe types of membrane proteins and their function

  4. Identify factors that influence mammalian membrane fluidity

  5. Discuss the function of membrane microdomains (lipid rafts, caveolae)

  1. Where are membranes found

    • outer barrier of cells and organelles

  2. What are the functions of membranes

    • has selective permeability

      • maintains gradient

    • allows intracellular cytoskeletal proteins and extracellular matrix components to attach to

  3. What makes up the structure of membranes

    • phospholipid bilayer

      • outer and inner leaflet

    • proteins

      • integral and peripheral membrane proteins

  4. What are the 2 main membrane components?

    • Lipids and Proteins

  5. What are the 3 subcategories of Lipids

    1. Phospholipids

    2. Cholesterol

    3. Glycolipids

  6. What type of compound are phospholipids?

    • polar, ionic compounds

  7. What are the 2 possible backbones can phospholipids have?'

    • Glycerol or Sphingosine

  8. Which of the phospholipid head and tail are hydrophilic and hydrophobic?

    • Head: Hydrophilic

    • Tail: Hydrophobic

  9. What are the 4 polar heads that can be attached to a GLYCEROL backbone?

    • Phosphatidyl-SERINE

    • Phosphatidyl-ETHANOLAMINE

    • Phosphatidyl-CHOLINE

    • Phosphatidyl-INOSITOL

  10. What polar head can be attached to a SPINGOSINE backbone?

    • Sphingomyelin

  11. Where is cholesterol located within the membrane?

    • between phospholipids

  12. What is the structure of cholesterol?

    • Hydroxyl group

    • Steroid nucleus

    • Hydrocarbon tail

  13. How is cholesterol oriented?

    • the Hydroxyl group end is oriented near the phospholipid heads

    • the steroid rings and hydrocarbon tails are parallel to the phospholipid tails

  14. What are Glycolipids

    • Lipids with a Carbohydrate attached

  15. How are Glycolipids oriented in the membrane?

    • The Glycolipid is embedded in the membrane with its Carbohydrate sticking outside

  16. What are Glycolipids concentration in comparison to Phospholipids and Cholesterol?

    • Lower concentration

  17. What are the roles of Glycolipids?

    • Intercellular Interactions

    • Blood Group Antigens

    • Receptors for Toxins

      • Cholera

      • Tetanus

  18. How can Integral Proteins be removed from the membrane structure?

    • the entire membrane structure needs to be disrupted

  19. What are Transmembrane proteins

    • proteins that pierce through the entire membrane

    • ex. GPCR, Ion Channels

  20. What are Lipid-Anchored membrane proteins?

    • proteins that are attached to the lipids and partially penetrate the membrane

    • ex. G proteins

  21. What are Peripheral Membrane proteins

    • proteins that are loosely attached to the inner membrane leaflet

    • ex. Cytoskeletal

  1. What are the 4 functions of membrane proteins

    1. Cell Adhesion

    2. Transport

      • Ion channel

    3. Signaling

      • Receptor

      • G proteins

    4. Structure

      • cytoskeleton

  2. What type of integral protein are G proteins?

    • Lipid-Anchored proteins

  3. What protein best describes the arrangement of a ligand receptor within a plasma membrane?

    • Transmembrane protein

  4. Distinguish the orientation of the phospholipid bilayer’s Outer and Inner Leaflet

    • Outer leaflet faces the exterior environment

    • Inner leaflet faces the cytosol

  5. What type of phospholipids that are part of the OUTER leaflet of the phospholipid bilayer?

    • Phosphatidyl-CHOLINE & Sphingomyelin

  6. What type of phospholipids that are part of the INNER leaflet of the phospholipid bilayer?

    • Phosphatidyl-SERINE

    • Phosphatidyl-Ethanolamine

    • Phosphatidyl-Inositol

  7. What indicates a normal functioning phospholipid bilayer?

    • Asymmetry of the outer and inner leaflets

  8. What happens if distribution of the phospholipids were placed in the wrong leaflet?

    • Apoptosis

  9. Why do phospholipids and proteins exhibit different types of motion?

    • Membrane Fluidity

  10. What are the 3 types of motions that Phospholipids have?

    • Flexion, Rotation, Lateral Movement

  11. What are the 2 types of motions that Proteins have?

    • Rotation and Lateral Movement

  12. How does Singer and Nicholson, 1972, described the membrane?

    • Fluid Mosaic Model

    • flowing sea and proteins dispersed

    • protein icebergs in a lipid sea

  13. What are Hemoglobinopathies

    • changes in lipid composition and/or defects in proteins associated with the red cell membrane

  14. What happens in a hemoglobinopathy where there’s defects in Spectrin and Ankyrin?

    • results in Elliptocytosis and Spherocytosis which can cause changes in shape

  15. What are Lipid Rafts

    • Microdomains that have Sphingolipids and Cholesterol

  16. What are Lipid Rafts’ functions?

    • Cholesterol transport

    • Endocytosis

    • Signal Transduction

  17. What are the 3 types of Lipid Rafts?

    • Planar

    • Glycosphingolipid-Enriched Membranes (GEM)

    • Caveolae

  18. What are Caveolae?

    • foldings of the plasma membrane of endothelial cells

  19. What are present in Caveolae?

    • Caveolin, Arachidonic Acid, Growth Factor Receptors, Integrins, Insulin Receptors