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Chapter 5a

Chapter 5a. Membrane Dynamics. About this Chapter. Mass balance and homeostasis Diffusion Protein-mediated, vesicular, and transepithelial transport Osmosis and tonicity The resting membrane potential Insulin secretion. Mass Balance in the Body. Intake. Excretion.

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Chapter 5a

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  1. Chapter 5a Membrane Dynamics

  2. About this Chapter • Mass balance and homeostasis • Diffusion • Protein-mediated, vesicular, and transepithelial transport • Osmosis and tonicity • The resting membrane potential • Insulin secretion

  3. Mass Balance in the Body Intake Excretion (through intestine,lungs, skin) (by kidneys, liver,lungs, skin) BODYLOAD Metabolism toa new substance Metabolicproduction Law of Mass Balance Intake ormetabolicproduction Excretion ormetabolicremoval Existingbody load – + Mass balance = Figure 5-2

  4. Mass Balance and Homeostasis • Clearance • Rate at which a molecule disappears from the body • Mass flow = concentration  volume flow • Homeostasis equilibrium • Living things not EQ across membranes • Osmotic equilibrium • Where? • Chemical disequilibrium • Electrical disequilibrium • Where?

  5. Homeostasis Figure 5-3a

  6. Homeostasis vsEqulibrium Compare: ECF vs ICF I vs P Figure 5-3b

  7. Diffusion • Map of membrane transport • Active vs Passive ENERGY REQUIREMENTS Uses energy of molecular motion. Does not require ATP Requires energy from ATP MEMBRANE TRANSPORT Diffusion Endocytosis Exocytosis creates concentration gradient for Secondary active transport Primary active transport Simple diffusion Facilitated diffusion Phagocytosis Molecule goes through lipid bilayer Mediated transport requires a membrane protein Uses a membrane-bound vesicle PHYSICAL REQUIREMENTS Figure 5-4

  8. Diffusion: Seven Properties • Passive process • High concentration to low concentration • Net movement until concentration is equal • Rapid over short distances • Directly related to temperature • How? • Inversely related to molecular size • In open system or across a partition • Membrane – composition related to function

  9. Simple Diffusion Figure 5-5

  10. Simple Diffusion Extracellular fluid Membrane surface area Concentration outside cell Molecular size Lipid solubility • Fick’s law of diffusion Concentration gradient Membrane thickness Composition of lipid layer Concentration inside cell Intracellular fluid Fick's Law of Diffusionsays: surface area • concentration gradient • membrane permeability Rate of diffusion membrane thickness Membrane permeability lipid solubility Membrane permeability molecular size Changing the composition of the lipid layer can increase or decrease membrane permeability. Figure 5-6

  11. Simple Diffusion Table 5-1

  12. Functions of Membrane Proteins • Structural proteins • Enzymes • Membrane receptor proteins • Transporters • Channel proteins • Carrier proteins

  13. Membrane Transport Proteins MEMBRANE PROTEINS can be categorized according to Structure Function Lipid- anchored proteins Integral proteins Peripheral proteins Membrane transporters Structural proteins Membrane enzymes Membrane receptors activate are active in are found in Carrier proteins Channel proteins are active in Receptor- mediated endocytosis Cell junctions Cytoskeleton change conformation form Signal transfer Open channels Gated channels Metabolism open and close Mechanically gated channel Chemically gated channel Voltage-gated channel Figure 5-7

  14. Membrane Transport Proteins Ligand binds to a cell membrane receptor protein. Ligand-receptor complex triggers intracellular response. Extracellular fluid Receptor Cell membrane Events in the cell Intracellular fluid Figure 5-8

  15. Membrane Transport Proteins MEMBRANE TRANSPORTERS Carrier proteins never form an open channel between the two sides of the membrane Channel proteins create a water-filled pore ECF Cell membrane Carrier open to ICF Same carrier open to ECF ICF can be classified can be classified Cotransporters Gated channels Open channels Uniport carriers Symport carriers Antiport carriers Open Closed Figure 5-9

  16. Membrane Channel Proteins One protein subunit of channel Channel Channel Figure 5-10

  17. Gating of Channel Proteins Chemically, voltage or mechanically controlled Closed gate Intracellular fluid Extracellular fluid Pacific Ocean Passage open to one side Gate closed Atlantic Ocean Molecule to be transported Carrier Membrane Transition state with both gates closed Pacific Ocean Atlantic Ocean Passage open to other side Pacific Ocean Atlantic Ocean Gate closed (b) (a) Figure 5-11

  18. Facilitated Diffusion of Glucose Figure 5-12

  19. Primary Active Transport • Primary Active Transporters • ATPases • Na/K pump • Ca • Secondary Active • Use potential energy • Na+ glucose • SGLT Figure 5-13

  20. Primary Active Transport • Mechanism of the Na+-K+-ATPase 1 ECF ATP ADP 5 2 3 Na+ from ICF bind ICF ATPase is phosphorylated with Pi from ATP. 2 K+ released into ICF Protein changes conformation. Protein changes conformation. 3 Na+ released into ECF 2 K+ from ECF bind 4 3 Figure 5-14

  21. Primary Active Transport 1 ECF 3 Na+ from ICF bind ICF Figure 5-14, step 1

  22. Primary Active Transport 1 ECF ATP ADP 2 3 Na+ from ICF bind ICF ATPase is phosphorylated with Pi from ATP. Figure 5-14, steps 1–2

  23. 1 ECF ATP ADP 2 3 Na+ from ICF bind ICF ATPase is phosphorylated with Pi from ATP. Protein changes conformation. 3 Na+ released into ECF 3 Primary Active Transport Figure 5-14, steps 1–3

  24. 1 ECF ATP ADP 2 3 Na+ from ICF bind ICF ATPase is phosphorylated with Pi from ATP. Protein changes conformation. 3 Na+ released into ECF 2 K+ from ECF bind 4 3 Primary Active Transport Figure 5-14, steps 1–4

  25. 1 ECF ATP ADP 5 2 3 Na+ from ICF bind ICF ATPase is phosphorylated with Pi from ATP. 2 K+ released into ICF Protein changes conformation. Protein changes conformation. 3 Na+ released into ECF 2 K+ from ECF bind 4 3 Primary Active Transport Figure 5-14, steps 1–5

  26. Secondary Active Transport • Mechanism of the SGLT Transporter 1 Na+ binds to carrier. 3 Glucose binding changes carrier conformation. Intracellular fluid Lumen of intestine or kidney SGLT protein [Na+] low [glucose] high [Na+] high [glucose] low 4 Na+ released into cytosol. Glucose follows. 2 Na+binding creates a site for glucose. Figure 5-15

  27. Secondary Active Transport 1 Na+ binds to carrier . Intracellular fluid Lumen of intestine or kidney SGLT protein [Na+] high [glucose] low [Na+] low [glucose] high Figure 5-15, step 1

  28. Secondary Active Transport 1 Na+ binds to carrier . Intracellular fluid Lumen of intestine or kidney SGLT protein [Na+] high [glucose] low [Na+] low [glucose] high 2 Na+ binding creates a site for glucose. Figure 5-15, steps 1–2

  29. Secondary Active Transport 1 Na+ binds to carrier . 3 Glucose binding changes carrier conformation. Intracellular fluid Lumen of intestine or kidney SGLT protein [Na+] high [glucose] low [Na+] low [glucose] high 2 Na+ binding creates a site for glucose. Figure 5-15, steps 1–3

  30. Secondary Active Transport 1 Na+ binds to carrier . 3 Glucose binding changes carrier conformation. Intracellular fluid Lumen of intestine or kidney SGLT protein [Na+] high [glucose] low [Na+] low [glucose] high 4 Na+ released into cytosol. Glucose follows. 2 Na+ binding creates a site for glucose. Figure 5-15, steps 1–4

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