Figure 7.17 EXTRACELLULAR FLUID

Today’s Topics Channel protein • Review Osmosis Solute • Facilitated Diffusion CYTOPLASM – Channel proteins Carrier protein – Carrier proteins • Active Transport – Na+/K+ pump • Endocytosis

Sept 19, 2012

Transmembrane transport proteins Aquaporin allow selective transport of hydrophilic molecules & ions 1. Channel protein

EXTRACELLULAR FLUID aqueous channel with hydrophilic pore

Channel protein Selective by size/charge Solute CYTOPLASM

(a)

Figure 7.15

For ions, the net driving force is the electrochemical gradient Gated Ion Channels move ions down an electrochemical gradient

+ + + + + + + + + + + + + + + + +++ ++++ ------

Several ------+++ +++ ways to + + + open the gates Voltage gated Ligand gated Mechanosensitive • has both a concentration and a charge component

1 Example: Ligand-gated ion channel Example of voltage-gated ion channel “Key to unlock gate” = acetylcholine K+ channel in neurons

Each kind has its own key

Transmembrane transport proteins Sodium Potassium pump 2. Carrier proteins Na+ Na+ Na+ Na+ + + + Na+ Na+ Na+ Na Na Na Can be used for active or passive transport

Solute Carrier protein + K+ K + (b) K+ K K+ K+ K+ K+

In contrast, channel proteins Moves Na+ out and K+ in, against gradient mediate only passive transport. Why?

Figure 7.19 Fig. 7-16-7 Passive transport Active transport EXTRACELLULAR [Na+] high ! Na+ ! + FLUID ! [K+] low ! Na !

Na+ ! Na+ ! Na+ !

+ Na+ ! Na ! Na+ ! + ATP [Na ] low ! P ! Na+ ! [K+] high! P ! CYTOPLASM ! ADP ! 1! 2! 3!

K+ !

K+ ! Diffusion Facilitated diffusion ATP K+ ! K+ ! K+ !

P ! K+ ! P ! 6! 5! 4!

2 Figure 7.22

Indirect Active Transport Phagocytosis Pinocytosis Receptor-Mediated Endocytosis – ! +! H+! EXTRACELLULAR ATP! + FLUID H ! Solutes – ! +! Pseudopodium Receptor + Proton pump ! H ! Plasma Ligand + membrane H ! Coat proteins

– ! +! Coated “Food” or pit + + other particle H ! – ! H ! Coated +! vesicle H+! Diffusion of H+! Sucrose-H+ cotransporter ! Vesicle + Food H ! vacuole – ! Sucrose ! +! CYTOPLASM – ! +! Sucrose !

….Each membrane has its own characteristic set of transporters

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