Ch 18.4

·         A molecular assembly in the __ carries out the synthesis of ATP
o   This enzyme complex was originally called the __ because it was discovered through its catalysis of the reverse reaction, the __
§  __ emphasizes its actual role in the mitochondrion. It is also called __

·         How is the oxidation of NADH coupled to the phosphorylation of ADP?
o   A method was suggested to be of the __
§  Proposal: __ and __ are couple by a __ across the inner mitochondrial membrane
·         The transfer of electrons through the __ leads to the __
·         The __ concentration becomes lower in the matrix, and an electric field with the __ __ is generated

·         Protons then do what?
o   This flow of protons drives __ by __
§  The energy-rich unequal distribution of protons is called the __, which can be thought of as being composed of two components: __ and __

o   A chemical gradient for protons can be represented as a __
o   The charge gradient is created by __ 

o   Mitchell proposed htat
§  __
·         Electron transport does generate a __ across the inner mitochondrial membrane
o   The pH outside is__ units lower than inside, and themembrane potential is __, the outside being __

·         The role of the respiratory chain was played by bacteriorhodopsin, a membrane protein from halobacteria that pumps proteins when illuminated
o   Synthetic vesicles containing bacteriorhodopsin and __ purified from beef heart were created
§  When the vesicles were __, ATP was formed
·         The __ and __ are biochemically separate systems, linked only by a __

·         Electron transport generates a __; and, __ by __ can be powered by a __
·         ATP synthase is a __. Much of the “stick” part, called the __, is embedded in the __. The 85-Angstrom-diameter ball, called the __, protrudes into the mitochondrial matrix
o   The F1 subunit contains the __
§  In fact, the isolated F1 subunits display __

·         The F1 subunit consists of __
o   The __ and __subunits, which makes up the bulk of the F1, are arranged alternately in a __; they are homologous to one another and are members of the P-loop NTPase family
§  Both bind __but only the __subunits participate directly in catalysis. 

·         Beginning ust below the __ and __ is a __.
o   The __subunit includes a long __ that extends into the center of the __
§  The __subunit breaks the symmetry of the __: each of the beta subunits is distinct by virtue of its interaction with a different face of gama

·         The __ is a hydrophobic segment that spans the __
o   F0 contains the __; this channel consists of a ring comprising from __subunits that are embedded in the membrane
§  A single __ binds to the outside of the ring

·         The F₀ and F₁ subunits are connected in two ways:

·         ATP synthase catalyze the formation of ATP from __ and __
o   The actual substrates are __

§  A __ of ADP attacks the __ of Pi to form a __intermediate, which then dissociates into ATP and H2O

o   Enzyme bound ATP forms reaily in the __
§  When ADP and P_i were added to ATP synthase in H2O, O became incorporated into P_i through the synthesis of ATP and its subsequent hydrolysis

·         The rate of incorporation of oxygen into Pi showed that about equal amounts of bound ATP an ADP are in equilibrium at the catalytic site, even in the absence of a proton gradient
o   ATP does not leave the catalytic site unless __
§  Thus, the role of the proton gradient is not to __ but to __

o   The fact that __ are components of the F1 moiety of the ATPase means that there are __, each performing one of three different functions at any instant. The proton-motive force causes the three active sites to do what as protons flow through the membrane-embedded component of the enzyme

o   The enzyme can be thought of as having a moving part and a stationary part:
§  The moving unit (rotor) consisting of the __
§  The stationary unit (stator) is composed of the remainder fo the molecule
o   The mechanism is a __
§  A __subunit can perform each of three sequential steps in the synthesis of ATP by changing conformation
What are they? 
§  Interactions with the __ make the three __ subunits unequivalent

o   At any given moment, one beta subunit will be in the__
§  This conformation does what?
§  A second subunit will be in the __
·         This conformation does what?

o   Both the T and L conformations are sufficiently __that they cannot __
§  The final subunit will be in the __
·         This form has a more __ and can __
o   The rotation of the gamma subunit does what?
§  ADP and Pi bound in the subunit in the __ are doing what?

o   Suppose:
§  The gamma subunit is rotated by 120 degrees in a counterclockwise direction
·         This rotation does what?
§  The L form site is __, enabling the transformation of __
·         The __in the __ can now depart from the enzyme to be replaced by ADP and Pi

·         An additional 120-degree rotation converts this __ into __, trapping these substrates
o   Each subunit progresses from the __ to the __ to the __ with no two subunits ever present in the same conformational form
§  This mechanism suggests what?

·         Rotation was determined through __, which allowed the __assembly to be immobilized on a glass surface that had been coated with nickel ions
o   This property of the tags allowed the a3b3 assembly to be immobilized on a glass surface that had been coated with nickel ions
§  The gamma subunit was linked to a fluorescently labeled __ to provide a long segment that could be observed under a microscope
o   The addition of ATP caused the actin filament to do what?             
§  the gamma subunit was __, driven by __

o   the gamma subunit rotates in __, each increment corresponding to the __
o   the enzyme appears to operate near __; that is, essentially all of the energy released by ATP hydrolysis is converted into __

·         How does proton flow through F0 drive the rotation of the gamma subunit?
o   The mechanism depends on the __
§  The stationary a subunit directly __
·         Although the structure of the a subunit has not yet been experimentally determined, a variety of evidence is consistent with a structure that includes two __

o   Thus, protons can pass into either of these channels, but they cannot __
§  The a subunit is positioned such that __

·         Structure of the c subunit: eaech poypeptide chain forms a pair of __ that __. An __ is in the middle of one of the helices
o   The key to proton movement across the membrane is that, in a proton-rich environment, a __ and will __
o   The c subunit with the bound proton then does what?

·         The movement of protons through the half-channels from the high proton concentration of the cytoplasm to the low proton concentration of the matrix powers the __
o   Its rotation is favored by the __
§  Thus, the c subunit with the __ moves from __ into the __; and, the other c subunits move in unison

o   The a unit does what as the c ring rotates. Each proton that enters the cytoplasmic half-channel of the a unit moves through the membrane by doing what?

·         How does the rotation of the c ring lead to the synthesis of ATP?
o   The c ring is tightly linked to the __
§  Thus, as the c ring turns, the __ in turn promotes the __through the binding-change mechanism
§  The rotation of the gamma subunit in turn promotes the __ through the __
·         The exterior column formed by the __ prevents the __ unit from rotating

o   The number of c subunits in the c ring appears to range between __, determining the number of protons that must be transported to generate a molecule of ATP
§  Each 360-degree rotation of the gamma subunit leads to the __
·         Thus, if there are 10 c subunits in the ring, each ATP generated requires the transport of __
o   __ must flow in for each ATP
o   Electrons from NADH pump enough protons to generate __, whereas those from FADH2 yield __

·         The __ and __ of ATP synthase are members of the P-loop NTPase family of proteins
o   The P-loop regions of the B subunits will bind either__ or __, depending on __. The conformational changes take place in an orderly way, driven by the __