Lecture 3 PP w/ Notes
Lecture 3 PP w/ Notes BIOL 2500
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This 31 page Class Notes was uploaded by Kelsey on Sunday September 11, 2016. The Class Notes belongs to BIOL 2500 at Auburn University taught by Dr. Shobnom Ferdous in Spring 2016. Since its upload, it has received 5 views. For similar materials see Human Anatomy & Physiology I in Biology at Auburn University.
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Date Created: 09/11/16
Transport Processes Ch. 3 1 Transport Processes • Plasma membrane is selectively (differentially) permeable – some molecules pass through easily, some do not • The way substances move across membrane depends on electrochemical gradient = concentration gradient + electrical gradient across plasma membrane & which direction substance needs to go 2 Diffusion • Collisions between molecules in areas of high concentration cause them to be scattered into areas with less concentration –Difference is called concentration gradient –Diffusion is movement of molecules down their concentration gradients (from high to low) • Energy is not required • Speed of diffusion is influenced by size of molecule and temperature 3 Main Types of Transport 1. Passive transport– no ATP needed; substances move down their concentration gradient (from high to low), 4 types 2. Active transport - ATP needed; ATP needed to move substances against their concentration gradient (from low to high), 3 types 4 Passive transport Diffusion -Diffusion itself just means tendency of substances to move from area of high concentration to area of low concentration 1. Simple diffusion – substances pass through lipid bilayer a. Lipid soluble molecules b. Small molecules c. substances include oxygen, carbon dioxide, lipid soluble vitamins 5 Diffusion (cont.) • Molecules have natural drive to diffuse down concentration gradients that exist between extracellular and intracellular areas • Plasma membranes stop diffusion and create concentration gradients by acting as selectively permeable barriers 6 1. Facilitated diffusion - substances move across membrane by protein channels or carrier proteins a. Glucose b. amino acids c. Ions • substances include glucose, amino acids, ions • carrier proteins specific for one substance • ions mostly through channels. example Na channel for transporting only Na 7 Clinical – Homeostatic Imbalance • If plasma membrane is severely damaged, substances diffuse freely into and out of cell, compromising concentration gradients • Example: burn patients lose precious fluids, proteins, and ions that weep from damaged cells 8 Passive transport 3. Osmosis – water moving through a semi-permeable membrane Osmolarity - total concentration of solutes in solution 9 • In the case where water freely moves by osmosis but membrane relatively impermeable to solutes, cell will take in or lose water depending on concentration of extracellular fluid relative to intracellular fluid 10 Osmosis In the case where water freely moves by osmosis but membrane relatively impermeable to solutes, cell will take in or lose water depending on concentration of extracellular fluid relative to intracellular fluid Which of these is used for most intravenous solutions? 11 Passive Transport 4. Bulk Flow (Filtration) – movement of solutes & water from high pressure to low pressure *Faster rate than diffusion & osmosis Example of bulk flow-in kidney 12 3.4 Active Membrane Transport • Two major active membrane transport processes – Active transport – Vesicular transport • Both require ATP to move solutes across a plasma membrane for any of these reasons: – Solute is too large for channels, or – Solute is not lipid soluble, or – Solute is not able to move down concentration gradient 13 Active Transport • Requires carrier proteins (solute pumps) – Bind specifically and reversibly with substance being moved – Some carriers transport more than one substance • Antiporters transport one substance into cell while transporting a different substance out of cell • Symporterstransport two different substances in the same direction • Moves solutes against their concentration gradient (from low to high) – This requires energy (ATP) 14 Active Transport (cont.) • Two types of active transport: – Primary active transport • Required energy comesd irectly from ATP hydrolysis – Secondary active transport • Required energy is obtainedndirectly from ionic gradients created by primary active transport 15 Active Transport 1. Bulk (Vesicular) transport- large substances transported in vesicles a. Endocytosis – bringing substance into the cell 1) Phagocytosis – engulfing molecules/bacteria (“ cell eating”) 2) Pinocytosis – engulfing water (“cell drinking”) b. Exocytosis – removing substance from the cell -Remember active transport requires ATP to move substances against their concentration gradient Vesicles- membranous sacs In exocytosis - secretory vesicle containing substance to be removed, moves to and fuses with plasma membrane, ruptures which expulses the contents 16 Phagocytosis - particle binds to receptors on cell surface, pseudopods (cytoplasmic extensions) develop and reach out to envelope particle forming a vesicle around the particle Pinocytosis - invagination of plasma membrane which surrounds extracellular fluid 17 Active Transport 2. Primary Active Transport – involves ATP and transport proteins to move substances against concentration gradient – Ex: Na /K ATPase pump (3 Na out for every 2 K in) 18 Solutes bind to the transport protein, ATP is split into ADP and P , provides energy for protein to change shape which “pumps” solute across the membrane against its electrochemical gradient http://www.youtube.com/watch?v=yz7EHJFDEJs 19 Active Transport (cont.) • Secondary active transport – Depends on ion gradient that was created by primary active transport system • Low Na concentration that is maintained inside cell by Na -K pump strengthens sodium’s drive to want to enter cell + • Na can drag other molecules with it as it flows into cell through carrier proteins (usually symporters) in membrane – Some sugars, amino acids, and ions are usually transported into cells via secondary active transport 20 Active Transport 3. Secondary Active Transport – simultaneous movement of 2 substances through transport protein; 1 provides energy to move other a. Co-transport (symport) – substances going in same direction b. Counter transport (antiport) – substances going in opposite direction 21 22 23 24 ****Membrane potential - difference in electrical charge across plasma membrane ******Resting membrane potential - membrane potential when cells in resting state ; ~-70 mV - inside of cell has overall negative charge relative to outside Extracellular Intracellular High Na+ Low Na + + Low K + High K++ High Ca ++ Low Ca - Low Cl - High Cl High Protein - Low Protein- 25 Establishing the potential The resting membrane potential is largely determined by differential permeability of plasma membrane to K and concentration gradient of K However, this passive process of K+ and Na+ moving across membrane would continue until their concentrations are equal across the membrane (electrochemical equilibrium). But this doesn’t occur because of active process (next slide) is this going to be a problem!!!! Need this voltage difference across the membrane+ ecause a change in membrane potential is what causes gh leaky channels bringing resting muscles to contract and what ~-70 mV propagates nerve impulses!!!! 26 Establishing the potential + ④ Na also enters cell through leaky channels bringing resting membrane potential to ~-70 mV 27 Repeat • The resting membrane potential is largely determined by differential permeability of plasma membrane to K and concentration gradient of K • However, this passive process of K+ and Na+ moving across membrane would continue until their concentrations are equal across the membrane (electrochemical equilibrium). But this doesn’t occur because of active process. • This would be a problem!!!! Need this voltage difference across the membrane because a change in membrane potential is what causes muscles to contract and what propagates nerve impulses!!!! 28 *****K is Key Player in RMP + + • K diffuses out of cell through K leakage channels down its concentration gradient • Negatively charged proteins cannot leave – As a result cytoplasmic side of cell membrane becomes more negative • K is then pulled back by the more negative interior because of its electrical gradient + • When drive for K to leave cell is balanced by its drive to stay, RMP is established – Most cells have an RMP around –90 mV 29 K is Key Player in RMP (cont.) + • In many cells, Na also affects RMP – Na is also attracted to inside of cell because of negative charge • If Na enters cell, it can bring RMP up to –70 mV + + + – Membrane is more permeable to K than Na , so K primary influence on RMP – • Cl does not influence RMP because its concentration and electrical gradients are exactly balanced 30 Maintaining the potential + + Na /K pumps (Active transport) maintains the resting membrane Na+ potential K+ -3 Na out for every + 2 K in 2 K+ 2 K+ 3 Na+ 3 Na+ 31
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