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55-140 (56)
Habetler (53)
Lecture

ION AND SOLUTE

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Department
Biological Sciences
Course
55-140
Professor
Habetler
Semester
Fall

Description
ION AND SOLUTE PUMPS Active transport to develop gradients Complex mechanisms due to energy coupling Slow transport rates, highly specific Variety of energy sources Light – rhodopsin Redox potential Decarboxylation Pyrophosphate hydrolysis **ATP** - ubiquitous Ion gradients drive many processes Mechanical Chemical (ATP synth) Signal trans. Chemiosmotic (glucose) Osmotic volume regulation BACTERIORHODOPSIN: light-driven proton pump Protons return to generate ATP Structure: 7TM helices enclose RETINAL (chromophore – light absorbing) Retinal divides proton conducting pathway in half Cytoplasmic – hydrophobic/narrow  barrier to proton movement Extracellular – hydrophilic/wide  allows proton to leave once halfway through D96 – pKa of 10  protonated under neutral circumstances D85 – pKa of 2  deprotonated usually Proton flow: Cytoplasm  D96  retinal  light driven isomerization  D85  another retinal conf. change  D85 pKa drops  extracellular **small conf. changes in retinal make it act as transient switch** similarities between pumping and signal transduction Electroneutral pumps: all energy of ATP hydrolysis (7.3 kcal/mol) goes into generating chem.. gradient electrogenic pumps squander much energy as membrane potential (elec. grad.) **can generate huge gradients using electroneutral pumps (H+/K+)** Transport ATPases: F – H+ transport to make ATP V (vacuolar) – ATP hydrolysis to transport H+ P – monovalent/divalent cation transport ABC – variety of substrate transport F TYPE ATP SYNTHASES freely reversible in vitro and in bacteria; counterproductive in eukaryotes (generate ion gradient for other processes) (only function is to make ATP  inhibitory protein binds under anoxic condition to prevent ATP hydrolysis) STRUCTURE: F1 – water soluble; catalyzes ATP hydrolysis (B-subunit) F0 – membrane embedded; conducts protons (via proton binding) FUNCTION: BINDING CHANGE MECHANISM - strongly cooperative and cyclical sequence of 3 catalytic sites o cycle only occurs if both tight and loose sites are bound - energy is required for cyclical activity tight – high affinity (binds A
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