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Transporters and Membranes

Transporters and Membranes. By Sushil Pal. Slides made using WMS transporters lecture, Molecules. Contents. Transports Types Properties Regulation Function Key examples (in my opinion) Membrane Potentials. Transport types?. Diffusion Passive Active Co-transport. Examples….

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Transporters and Membranes

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  1. Transporters and Membranes By Sushil Pal Slides made using WMS transporters lecture, Molecules

  2. Contents • Transports • Types • Properties • Regulation • Function • Key examples (in my opinion) • Membrane Potentials

  3. Transport types?

  4. Diffusion • Passive • Active • Co-transport

  5. Examples….

  6. Properties of Transporters • Transporters are integral membrane proteins. • Transporters are channels or carriers…. • What is the difference between these? • Transporters are specific (or selective)… • What ways are they specific/selective? • Transporters are regulated. • Transporters are passive or active

  7. The effect of Transporters on physiological processes…??

  8. Uptake of metabolites. • Extrusion of waste products. • Maintenance of intracellular pH. • Generation and use of ion gradients. • Regulation of cell volume.

  9. Transporter regulation…??

  10. Voltage gated – membrane potentials • Ligand gated – neurotransmitters – Ach • Mechanically gated – sound, touch

  11. Passive and Active transport differences…?

  12. Passive • No metabolic energy use • Down a concentration gradient • Eg. Na+ entry into cells during AP • Active • Metabolic energy use - ATP • Against a concentration gradient • Eg. H+ movement in electron transport chain

  13. Important passive transporters.. • GLUT • Function: move and trap glucose into cells 2) Cl-/HCO3- anion exchanger • Function: regulate pH • Found in erythrocytes

  14. Important Active Transporters • Plasma membrane Ca2+-ATPase. • Sarcoplasmic/endoplasmic reticulum Ca2+-ATPase – for 2ndary messengers • Plasma membrane Na+:K+-ATPase • Plasma membrane H+:K+-ATPase – parietal cells – acidic environment

  15. Uniport Symport Antiport Co-transport systems Co Transporters

  16. Found in many locations to help different cellular functions • Do you know any co-transporters..?

  17. Na+symporters • Glucose uptake (small intestine and kidney). • Amino acid uptake (luminal epithelial cells). • Cl- uptake (epithelial cells in small intestine). • HCO3- uptake (regulates cell pH in many cell types). • Na+antiporters • H+ export (regulates cell pH in most cell types). • Ca2+ export (muscle cells). • Na+-dependent anion exchanger • Na+ & HCO3- influx and H+ & Cl- efflux

  18. Ion concentrations • I recommend learning these..

  19. - + - + - + - + - + - + - + - + Membrane potential = -70 mV Ion concentrations in a typical cell [K+] 160 mM [K+] 5 mM [A-] 165 mM [A-] 40 mM [Na+] 150 mM [Na+] 10 mM Most organic molecules are negatively charged. [Cl-] 115 mM [Cl-] 5 mM [Ca2+] 2 mM [Ca2+] 0.2 M

  20. Simplified Nernst equation at 37°C 61 mV [ion]out Eion = log [ion]in Z Nernst equation..simplified • You should learn this too and know what the value means. • Your group work will run through more examples than your lecture

  21. 61 mV 5 mM EK = log 1 160 mM EK = -91.8 mV Using the Nernst equation for K+ at 37°C 61 mV [ion]out Eion = log [ion]in Z Note: normal K+ con is 5mM outside the cells If [K+]out increases to 10 mM (hyperkalaemia), Ek is –73 mV. Can result in ventricular arrhythmia and fibrillation.

  22. Therefore an increase in extracellular K+ concentration will bring the membrane potential closer the threshold meaning the Action Potential will be easier to fire thus fibrillation and arrhythmias

  23. Learn the action potential process!! • Ie which channels are involved, what moves in and out etc • It has come up in exams!!

  24. Membrane potential • Depolarisation is a decrease in membrane potential. • Cytoplasmic side of the membrane becomes LESSnegative ie close to 0 • Opening Na+ (or Ca2+) channels depolarises cells. • Na+ (and Ca2+) ions flow into the cell. • Hyperpolarisationis an increase in membrane potential. • Cytoplasmic side of the membrane becomes MOREnegative ie further from 0 • Opening K+ or Cl- channels hyperpolarises cells. • K+ ions flow out of the cell, Cl- ions flow into the cell.

  25. Refectory Periods.. • Which types are they? • Why are they important?

  26. Refractory periods Membranes are refractory to stimulation during the action potential. This is the absolute refractory period. The membrane becomes more responsive as it repolarises. Very strong depolarisation produces a second action potential. This is the relative refractory period. Absolute Relative refractory period +60 +40 +20 0 Membrane potential (mV) -20 -40 -60 -80 0 1 2 3 4 Time (ms)

  27. Advice • Learn all the different types of transporters and channels in your lectures. • As the year goes on you will come across them again and again so learning them in context will be more useful than in isolation. • Getting you head around membrane potential is useful in Semester 2

  28. Any questions??

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