Chapter 5 a Membrane Dynamics About this Chapter

Chapter 5 a 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 (through intestine, lungs, skin) (by kidneys, liver, lungs, skin) BODY LOAD Metabolic production Metabolism to a new substance Law of Mass Balance Mass balance = Existing + body load Intake or metabolic production – Excretion or metabolic removal Figure 5 -2

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?

Homeostasis Figure 5 -3 a

Homeostasis vs Equlibrium Compare: ECF vs ICF I vs P Figure 5 -3 b

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

Diffusion: Seven Properties 1. Passive process 2. High concentration to low concentration 3. Net movement until concentration is equal 4. Rapid over short distances 5. Directly related to temperature • How? 6. Inversely related to molecular size 7. In open system or across a partition • Membrane – composition related to function

Simple Diffusion Figure 5 -5

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

Simple Diffusion Table 5 -1

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

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

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

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

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

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

Facilitated Diffusion of Glucose Figure 5 -12

Primary Active Transporters • ATPases • Na/K pump • Ca Secondary Active Use potential energy • Na+ glucose • SGLT

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

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

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

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

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

Primary Active Transport 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. 4 2 K+ from ECF bind Protein changes conformation. 3 3 Na+ released into ECF Figure 5 -14, steps 1– 5

Secondary Active Transport • Mechanism of the SGLT Transporter 1 Na+ binds to carrier. Lumen of intestine or kidney Intracellular fluid 3 Glucose binding changes carrier conformation. 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

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

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

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

Secondary Active Transport 1 Na+ binds to carrier. Lumen of intestine or kidney Intracellular fluid 3 Glucose binding changes carrier conformation. 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