BIOL2P03 Lecture 4 - Biomembranes 2024 PDF

Cell Biology: Principles of Cell Function BIOL2P03 - Winter 2024 Lecture 4 - Biomembranes Chapter 7: Biomembranes Testable material: Slides 4-8, 20-32 Chapter 7: Biomembranes Chapter 7: Biomembranes Biomembranes consist of: 1) a lipid bilayer 2) embedded proteins, glycoproteins and gl...

Cell Biology: Principles of Cell Function BIOL2P03 - Winter 2024 Lecture 4 - Biomembranes Chapter 7: Biomembranes Testable material: Slides 4-8, 20-32 Chapter 7: Biomembranes Chapter 7: Biomembranes Biomembranes consist of: 1) a lipid bilayer 2) embedded proteins, glycoproteins and glycolipids Extracellular Fluid Chapter 7: Biomembranes Vesicle Chapter 7: Biomembranes Biomembranes perform several important functions in the cell ▫Lipid bilayer provides selective permeability Embedded proteins participate in ▫Cell signaling ▫Cell-Cell and cell-matrix adhesions ▫Energy transduction Glycolipids and glycoproteins allow for cell recognition Chapter 7: Biomembranes  Synthetic Biology: RNA as a molecular building block - virus assembly COVID-19 Structure: RNA Serves as a Scaffold for Viral Assembly http://pdb101.rcsb.org/sci-art/goodsell-gallery/coronavirus Synthetic Biology: RNA as a molecular building block - virus assembly Synthetic Biology: RNA as a molecular building block - virus assembly Dr. John Briggs, LMB Cambridge Synthetic Biology: RNA as a molecular building block - virus assembly Dr. John Briggs, LMB Cambridge  Synthetic Biology: RNA as a molecular building block - virus assembly Dr. Martin Beck Max Planck Institute, Frankfurt  Synthetic Biology: RNA as a molecular building block - virus assembly Dr. Martin Beck Max Planck Institute, Frankfurt Chapter 7: Biomembranes Glycolipids and glycoproteins allow for cell recognition Chapter 7: Biomembranes Glycolipids and glycoproteins allow for cell recognition Chapter 7: Biomembranes Glycolipids and glycoproteins allow for cell recognition Biomembranes: The Lipid Bilayer - Composition The lipid bilayer is primarily made up of phospholipids Phospholipids are amphipathic molecules that contain a hydrophilic phosphate head group and hydrophobic tail groups ▫ Organized so that hydrophobic tails are shielded from water  Biomembranes: The Lipid Bilayer - Composition Phosphoglycerides are the most abundant phospholipids in eukaryotic biomembranes Each consists of ▫ Phosphate group attached to variable head group (R) ▫ Glycerol ▫ Fatty acids Biomembranes: The Lipid Bilayer - Composition Biomembranes: The Lipid Bilayer - Composition Sphingolipids and cholesterol are also amphipathic molecules commonly found in eukaryotic biomembranes Biomembranes: The Lipid Bilayer - Leaflets Each layer of the lipid bilayer is known as a leaflet ▫ Can have different compositions of leaflets Biomembranes: The Lipid Bilayer - Fluidity The lipid bilayer exhibits fluidity ▫ Phospholipids can readily move laterally within each leaflet ▫ Can also rotate or wave Biomembranes: The Lipid Bilayer - Fluidity The degree of fluidity is dependent upon ▫ Temperature ▫ Composition of the lipid bilayer The membrane is gel-like at low temperatures and becomes more fluid at higher temperatures Biomembranes: The Lipid Bilayer - Fluidity Fatty acids are long hydrocarbon chains Saturated fatty acids do not contain any carbon-carbon double bonds and can pack together closely Unsaturated fatty acids contain one or more carbon-carbon double bonds that place a kink in the hyrdocarbon chain ▫Makes it more difficult for fatty acids to pack together Biomembranes: The Lipid Bilayer - Fluidity The greater the amount of unsaturated fatty acids in the lipid bilayer, the greater the fluidity Biomembranes: The Lipid Bilayer - Fluidity Long fatty acids provide more intermolecular interactions between phospholipids The greater the proportion of long fatty acids, the lower the fluidity of the biomembrane Longer fatty acids also increase the thickness of the lipid bilayer Biomembranes: The Lipid Bilayer - Fluidity Cholesterol stabilizes the membrane and prevents it from becoming too fluid or too gel-like Biomembranes: The Lipid Bilayer - Fluidity Fluidity of the lipid bilayer allows embedded proteins to move laterally within the membrane ▫ Enables proteins to interact with their targets Biomembranes: The Lipid Bilayer - Lipid Rafts Not all regions of the lipid bilayer exhibit the same degree of fluidity Lipid rafts are small segments of the lipid bilayer that contain a high degree of cholesterol and are therefore more stable ▫ Lipid rafts often contain proteins involved in cell signaling end