L2 Cell Membranes

Page 3: Lecture Outline

• Topics:

  • Fluid Mosaic Model of Cell Membrane

  • Different types of membrane lipids

  • Important chemical features of membrane components for function

  • Cholesterol and Lipid Rafts

  • Bilayer asymmetry

  • Enzymes: Flipases, Flopases, Scramblases

  • Phospholipases

  • Signalling Lipids

Page 4: Learning Outcomes

• Key Goals:

  • Understand the role of the cell membrane in cell functions

  • Identify components of the membrane influencing structure and function

  • Comprehend lipid asymmetry's influence on cell function

  • Describe generation of lipid asymmetry

  • Recognize how bioactive lipids affect membrane proteins

Page 5: Fluid Mosaic Model of Cell Membrane

• Composition:

  • Cholesterol

  • Glycolipid

  • Protein channels and transport proteins

  • Globular proteins (integral and peripheral)

  • Cytoskeletal filaments

• Structure:

  • Amphipathic phospholipids within a bilayer

  • Hydrophilic heads and hydrophobic tails

  • Extracellular fluid, cytoplasm, and surface proteins

Page 6: Characteristics of Fluid Mosaic Model

• Key Features:

  • Two molecules thick of phospholipids

  • Separates cell contents from the external environment

  • Offers fluidity and elasticity

• Regulatory Domains:

  • Involved in cell signaling, apoptosis, membrane budding, and fusion

Page 7: Chemical Structures of Lipids

• Types:

  • Phospholipids and Glycolipids

• Structures:

  • Non-polar and polar groups

  • Nitrogenous bases and variable sugar chains

Page 8: Phospholipids

• Head Groups:

  • Includes amines and serine

  • Inositol and glycerol

• Tail Groups:

  • Varied chain lengths (C16, C18, etc.)

Page 9: Arrangement in Bilayer

• Layers:

  • Outer and inner leaflets

• Properties Influences:

  • Polar region affects lipid packing

  • Non-polar region influenced by cholesterol and saturation levels

Page 10: Lipid Composition Variability

• Differences in Cells:

  • Composition of inner vs. outer leaflets

  • Charge distribution: more negatively charged lipids in inner leaflet

  • Variability in cholesterol levels and fluidity in neuronal membranes

Page 11: Lipid Rafts

• Definition:

  • Specialized regions of less fluidity in membranes

  • Important in trafficking and signaling

Page 12: Characteristics of Lipid Rafts

• Location:

  • Found only in the outer leaflet

• Composition:

  • Contain sphingolipids and cholesterol

  • Thicker than standard membranes with saturated acyl chains

• Protein Interaction:

  • Proteins associate with rafts to facilitate signaling

Page 13: Cholesterol's Role

• Function:

  • Affects general membrane properties and specific protein functions

  • Example: Cholesterol inhibits the Dopamine Transporter by binding in a critical region

Page 14: Lipid Asymmetry Maintenance

• Process:

  • Achieved via ATP and enzymes:

  • Flippases (move lipids inward), Floppases (move lipids outward), Scramblases (no energy required)

Page 15: Flipping Mechanism of Bacterial Flippase

• Process Overview:

  • PglK enzyme flips lipid-linked sugar molecules using ATP

  • Involves conformational changes and engagement of lipids with the membrane

Page 16: Phosphatidyl-serine and Apoptosis

• Role in Cell Death:

  • PS acts as an