Cell Biology: Principles of Cell Function BIOL2P03 Lecture 6 2024 PDF

Cell Biology: Principles of Cell Function BIOL2P03 - Winter 2024 Lecture 4 - Membrane Transport Chapters 11 & 12: Membrane Transport and Excitable Cells Testable material: All slides Chapters 11 & 12: Membrane Transport & Excitable Cells Chapters 11 & 12: Membrane Transporters: Doorways to the...

Cell Biology: Principles of Cell Function BIOL2P03 - Winter 2024 Lecture 4 - Membrane Transport Chapters 11 & 12: Membrane Transport and Excitable Cells Testable material: All slides Chapters 11 & 12: Membrane Transport & Excitable Cells Chapters 11 & 12: Membrane Transporters: Doorways to the Cell Protein-mediated Transport Chapters 11 & 12: Protein-mediated Transport Chapters 11 & 12: Protein-mediated Transport Chapters 11 & 12: Protein-mediated Transport Chapters 11 & 12: Protein-mediated Transport Chapters 11 & 12: Protein-mediated Transport Protein-mediated transport can also be categorized based on the direction that molecules move Facilitated transport is the movement of molecules down their concentration gradients using integral membrane proteins, including uniporters and ion channels Active transport is the movement of molecules against their concentration gradient by ATP-powered pumps Co-transport is the movement of one molecule against its concentration gradient while the other molecule moves down its concentration gradient ▫ Performed by symporters and antiporters Membrane Transporters Chapters 11 & 12: Membrane Transporters Chapters 11 & 12: Membrane Transporters Chapters 11 & 12: Membrane Transporters Chapters 11 & 12: Membrane Transporters Transporters exhibit saturation when there is a high concentration of the molecule to be transported Facilitated Transport Simple Diffusion Glucose Transporters Chapters 11 & 12: Glucose Transporters Glucose is the main source of energy for eukaryotic organisms Energy production from glucose occurs inside of the cell Glucose must therefore be transported from the extracellular fluid into the cytosol Achieved using a diverse family of transporter proteins ▫GLUT proteins ▫Sodium-coupled glucose transporters (SGLTs) Chapters 11 & 12: Glucose Transporters GLUT proteins are uniporters that move glucose down its concentration gradient ▫ A low concentration of glucose is achieved inside of the cell by rapidly converting glucose to glucose-6-phosphate Chapters 11 & 12: Glucose Transporters There are 14 different isoforms of GLUT proteins ▫ Each has slightly different properties ▫ Cells will express specific GLUT proteins to meet their unique needs Chapters 11 & 12: Glucose Transporters Cells can also regulate the number of GLUT proteins in the plasma membrane to modify the amount of glucose uptake ▫ GLUT-4 inserts itself into the membrane when insulin is present Chapters 11 & 12: Glucose Transporters Sodium-coupled glucose transporters move glucose against its concentration gradient and sodium down its concentration gradient ▫ Symporter – both molecules move into the cell ▫ Secondary active transport Allows cells that have a high cytosolic glucose concentration to still obtain glucose from their environment Important for epithelial cells lining the gastrointestinal tract that want to absorb glucose from food and send it to the bloodstream Chapters 11 & 12: Glucose Transporters Water Transport Chapters 11 & 12: Water Transport Similar to ions, water will spontaneously flow down its concentration gradient across a membrane that is permeable to it To determine the direction that water will flow, we need to know the osmolarities of the solutions on both sides of the membrane Osmolarity is defined as the number of solute particles per unit volume ▫ Uses units of Osm/L Different from concentration which is the number of molecules per unit volume ▫ Uses units of mol/L Chapters 11 & 12: Water Transport If we have a molecule that dissociates into two or more particles when placed in water, the concentration of the solution will be different than the osmolarity Consider a 150 mM solution of NaCl ▫ When NaCl is dissolved in water each molecule of NaCl generates one Na+ particle and one Cl- particle ▫ The osmolarity of this solution would therefore be 300 mOsm/L Chapters 11 & 12: Water Transport Water is a polar molecule that is only slightly permeable to the lipid bilayer To accelerate water transport, most biomembranes possess water transporters known as aquaporins Chapters 11 & 12: Water Transport The movement of water across the membrane influences cell size ▫ Cells placed in dilute solutions will swell, while those placed in concentrated solutions will shrink ATP-Powered Pumps Chapters 11 & 12: ATP-Powered Pumps ATP-Powered Pumps generate concentration gradients in the cell Chapters 11 & 12: ATP-Powered Pumps Use energy from ATP to move molecules against their concentration gradients ▫Exception = F-class pumps ATP-Powered Pumps generate concentration gradients in the cell Four main classes exist: ▫P-class pumps ▫V-class proton pumps ▫F-class proton pumps ▫ABC superfamily Chapters 11 & 12: ATP-Powered Pumps: P-class Pumps P-class pumps move ions against their concentration gradients using energy from ATP ATP is used to phosphorylate the cytosolic face of the pump protein This results in a conformational change that causes ion transport ▫Examples include: ▫Sodium/Potassium ATPase (Na+/K+-ATPase), and Ca2+-ATPases Chapters 11 & 12: ATP-Powered Pumps: P-class Pumps Na+/K+-ATPase Chapters 11 & 12: ATP-Powered Pumps: P-class Pumps Na+/K+-ATPase Chapters 11 & 12: ATP-Powered Pumps: P-class Pumps Ca2+-ATPase Chapters 11 & 12: ATP-Powered Pumps: P-class Pumps Ca2+-ATPase Chapters 11 & 12: ATP-Powered Pumps: V-class Proton Pumps Chapters 11 & 12: ATP-Powered Pumps: V-class Proton Pumps Pump protons (H+ ions) against their concentration gradient using energy from ATP ▫ Used by lysosomes to generate an acidic internal environment that is required by the degradative enzymes they contain Chapters 11 & 12: ATP-Powered Pumps: F-class Proton Pumps Chapters 11 & 12: ATP-Generating Pumps: F-class Proton Pumps Typically function in the reverse direction of V-class proton pumps Protons move down their concentration gradient and the energy released in the process is used to synthesize ATP ▫ E.g. ATP synthase Chapters 11 & 12: ABC Transporters Transport ions and small molecules ▫ E.g. carbohydrates, phospholipids, amino acids Most diverse group of ATP-powered pumps Can transport certain drugs out of the cell ▫ E.g. chemotherapeutic agents from cancer cells Chapters 11 & 12: ABC Transporters end