The Proton-Motive Force 16-1,617

The Proton-Motive Force16-1,617

Protons move indifferent directionsto make ATP, butsame general idea,same shape tomolecules16-2, 618

Not muchnew here, exceptthat howpathways integrateand checkpointsof individualenzymes muchmore refined now16-3, 620

Mitochondria oftenare not littlekidney-beans, asalways shown (16-7,622)—they cananastomose and change shapewith cell-may be one hugemitochondrion in cell-what implications does thathave for mitochondrial replication?

Hoffman and Avers, 1973Science 181:749-751

http://www.sci.sdsu.edu/TFrey/MitoMovie.htm

http://www.sci.sdsu.edu/TFrey/MitoMovie.htm

Outer stuff is er, inner stuff different segments of cristae

Fig 16-9, 624 to orient you as to where things are-(outer membrane not shown)getting things in and out of mitochondria importantflux points (e.g. fatty acids)

Electron transport chain-protons pumped while electrons passed downenergy gradient16-19, 636

Cytochrome C oxidase-terminal electron acceptor13 subunits (3 shown here fig 16-23 p. 638)3 made by mitochondria, 10 by nucleus

slime mold adjustnumber of unitsto oxygentension in environment(eg. Burke and Poyton, 1998,J.Exp. Biol. 201:1163-75)

16-27,29;643-4Isolate FoF1 complex and artificially impose pH gradient-makes ATP

Reverse pH gradient and ATP is split

F1 only is atpaseF0 only is proton channel

F1F0 complexis a littlemachine

16-28, 644

16-30, 645 ATP synthesis-top down view

1) O=open, L=low affinity, T=tight affinity2) first panel, ADP + P bind to beta 1 subunit3) protons flowing through FO causes gamma subunitto rotate 120 degrees-that causes conformational changein beta subunits4) beta 1 goes from O to L, B2 from O-T (releasing ATP)and beta 3 from L-T5) ATP synthesized in beta 3 –does not require energy6) etc.

Exquisite proof of this model--attached purified F1F0 to slide-F1 side down-attached fluorescent actin filaments to gamma subunit-add ATO and actin whirls around-decrease concentration of ATP gradually, and youcan get it tomove slowly in120 degreeincrements 16-31, 646

Check out:http://www.cnr.berkeley.edu/~hongwang/Project/ATP_synthase/

(play movies)

Uncoupling proteins-destroy proton gradient byproviding alternate channel for protons acrossinner mito membrane. UCP-1=thermogenin-brown fat

UCP2,3= many tissues

Group Exercise 4

Read the provided material from a 1986 version ofyour textbook, then write a short paragraph onthe advances made in the field of ATP synthesissince 1986.