MCB 2000 Quiz 8 (chapters 20 and 21)

Oxidative phosphorylation captures the energy of high-energy electrons to

synthesize ATP

The flow of electrons from NADH and FADH2 to O2 occurs

in the electron-transport chain or respiratory chain.

_____ set of _______-____ rxns generates a _____ _________.

exergonic
oxidation-reduction
proton gradient

The proton gradient is used to?

•power the synthesis of ATP.

cellular respiration/ respiration

the citric acid cycle and oxidative phosphorylation

Describe oxidative phosphorylation

Oxidation and ATP synthesis are coupled by transmembrane proton fluxes. The respiratory chain (yellow structure) transfers electrons from NADH and FADH2 to oxygen and simultaneously generates a proton gradient. ATP synthase (red structure) converts the energy of the proton gradient into ATP.

The ___ ___ ___ and ___ _____ occur in the _______

The electron-transport chain and ATP synthesis occur in the mitochondria

•Where does the citric acid cycle occur? Glycolysis?

The outer mitochondrial membrane is permeable to most small ions and molecules because of the channel protein called?

mitochondrial porin

The inner membrane, which is folded into ridges called ___ is ____ to most molecules

cristae
impermeable

-Average surface are of a human being is 1.7 m2. How much surface area is there in all the mitochondria in a person?

The inner membrane is the site of?

electron transport and ATP synthesis.

The Electron-Transfer Potential of an Electron Is Measured as

Redox Potential

reduction potential, E0

a measure of a molecule's tendency to donate or accept electrons.

strong reducing agent

readily donates electrons and has a negative E0

strong oxidizing agent

readily accepts electrons and has a positive E0′.

standard free-energy change

related to the change in reduction potential.

n

number of electrons transferred

F

the Faraday constant (96.48 kJ/mol*V).

Describe measurement of Redox Potential

Electrons flow through the wire connecting the cells, whereas ions flow through the agar bridge.

oxidant

acceptor of electrons in an oxidation-reduction reaction.

reductant

donor of electrons in an oxidation-reduction reaction.

Energy is released when ___.

high-energy electrons are transferred to oxygen.

The energy is used to establish a?

proton gradient

The electron-transport chain is composed of?

•four large protein complexes.

The electrons donated by NADH and FADH2 are passed to

electron carriers in the protein complexes.

The carriers include

flavin mononucleotide (FMN), iron associated with sulfur in proteins (iron-sulfur proteins), iron incorporated into hemes that are embedded in proteins called cytochromes, and a mobile electron carrier called coenzyme Q (Q).

Electron flow within the complexes in

•in the inner mitochondrial membrane generate a proton gradient.

.The electron carrier component is the same in both

flavin mononucleotide and flavin dinucleotide (FAD

Components of the Electron-Transport Chain

Electrons flow down an energy gradient from NADH to O2. The flow is catalyzed by four protein complexes. Iron is a component of all of the complexes as well as cytochrome c.

Structure of Iron-Sulfur Clusters

(A) A single iron ion bound by four cysteine residues.
(B) 2Fe-2S cluster with iron ions bridged by sulfide ions.
(C) 4Fe-4S cluster. Each of these clusters can undergo oxidation-reduction reactions

Coenzyme Q is derived from

isoprene

Coenzyme Q binds ----- and ---- andcan exist in several --- ----

1) protons (QH2) as well as electrons
2)•oxidation states.

Oxidized (Q) and reduced Q (QH2) are present in the

mitochondrial membrane

the Q pool.

inner mitochondrial membrane

Oxidation States of Quinones

The reduction of ubiquinone (Q) to ubiquinol (QH2) proceeds through a semiquinone intermediate (QH•).

Electrons flow from NADH to O2 through

three large protein complexes embedded in the inner mitochondria membrane

the complexes pump protons out of the ____ generating a ______

mitochondria,
proton gradient

The proton pumping complexes are

•NADH-Q oxidoreductase (Complex I)
•Q-cytochrome c oxidoreductase (Complex III)
Cytochromecoxidase (Complex IV

Succinate-Q reductase (Complex II) is not a proton pump, but it does what?

deliver electrons from FADH2 to Complex III via Ubiquinone.

The electrons from NADH are passed along to Q to form

QH2 by Complex I

QH2 leaves the enzyme for the Q pool in

•the hydrophobic interior of the inner mitochondrial membrane.

Four protons are simultaneously pumped out of the

mitochondria by Complex

two protons are tied up in

the created QH2 molecule - this also contributes to proton motive force

Electron-Proton Transfer Reactions Through NADH-Q Oxidoreductase

Coupled electron-proton transfer reactions through NADH-Q oxidoreductase. Electrons flow in Complex I from NADH through FMN and a series of iron-sulfur clusters to ubiquinone (Q), forming Q2−. The charges on Q2− are electrostatically transmitted to hydrophilic amino acid residues (shown as red and blue balls) that power the movement of HL and bH components. This movement changes the conformation of the transmembrane helices and results in the transport of four protons out of the mitochondrial matrix

Succinate dehydrogenase of the citric acid cycle is a part of the

succinate-Q reductase complex (Complex II).

The FADH2 generated in the citric acid cycle reduces Q

to QH2, which then enters the Q pool.

Complex II is not

a proton pump

Electrons from QH2 are used to reduce?

•two molecules of cytochrome c in a reaction catalyzed by the Q-cytochrome c oxidoreductase or Complex III.

Complex III is

a proton pump

QH2 carries ___ whereas cytochrome c carries only ___

two electrons
•one electron.

The mechanism for coupling electron transfer from QH2 to cytochrome c is called

Q cycle

In one cycle

four protons are pumped out of the mitochondria and two more are removed from the matrix (via formation of QH2).

describe the Q Cycle

In the first half of the cycle, two electrons of a bound QH2 are transferred, one to cytochrome c and the other to a bound Q in a second binding site to form the semiquinone radical anion Q•-. The newly formed Q dissociates and enters the Q pool. In the second half of the cycle, a second QH2 also gives up its electrons, one to a second molecule of cytochrome cand the other to reduce Q•- to QH2. This second electron transfer results in the uptake of two protons from the matrix.

what does Cytochrome c oxidase accept?

•four electrons from four molecules of cytochrome c in order to catalyze the reduction of O2 to two molecules of H2O.

chemical protons

four protons used to reduce oxygen

four protons are pumped into the

intermembrane space

Cytochrome c Oxidase Mechanism

The cycle begins and ends with all prosthetic groups in their oxidized forms (shown in blue). Reduced forms are in red. Four cytochrome c molecules donate four electrons, which, in allowing the binding and cleavage of an O2 molecule, also makes possible the import of four H+ from the matrix to form two molecules of H2O, which are released from the enzyme to regenerate the initial state

Proton Transport by Cytochrome cOxidase

Four protons are taken up from the matrix side to reduce one molecule of O2 to two molecules of H2O. These protons are called "chemical protons" because they participate in a clearly defined reaction with O2. Four additional "pumped" protons are transported out of the matrix and released on the cytoplasmic side in the course of the reaction. The pumped protons double the efficiency of free-energy storage in the form of a proton gradient for this final step in the electron-transport chain.

Electron-Transport Chain

High-energy electrons in the form of NADH and FADH2 are generated by the citric acid cycle. These electrons flow through the respiratory chain, which powers proton pumping and results in the reduction of O2.

Why are the electrons carried by FADH2 not as energy-rich as those carried by NADH? What is the consequence of this difference?

Reduction potential is more positive. Less energy is released when the electrons are passed along. The consequence is less protons pumped. NADH produced 2.5 ATP and FADH2 produces only 1.5 ATP

Amytal is a barbiturate sedative that inhibits electron flow through Complex I. How would the addition of amytal to actively respiring mitochondria affect the relative oxidation-reduction states of the components of the electron-transport chain and the citric acid cycle?

Complex I gets reduced, but can't pass on the electrons. Everyone else remains oxidized. ETC shuts down. Citric acid cycle shuts down.

Two copies each of Complex I, Complex III, and Complex IV appear to be associated with one another in what is called the

respirasome

The area at the mouth of the Mississippi is nutrient-rich because of

agricultural runoff

Phytoplankton and aerobic bacteria proliferate to such an extent that

•oxygen concentration in the water falls. Fish cannot survive under these conditions.

Partial reduction of O2 generates

highly reactive oxygen derivatives called reactive oxygen species (ROS)

ROS are implicated in

pathological conditions

ROS include

superoxide ion
peroxide ion
and
hydroxyl radical

Two to four percent of oxygen molecules consumed by mitochondria are converted into

superoxide ions.

Superoxide dismutase and catalase help protect against

ROS damage

Dismutation

a reaction in which a single reactant is converted into two different products.

Superoxide Dismutase Mechanism

The oxidized form of superoxide dismutase (Mox) reacts with one superoxide ion to form O2 and generate the reduced form of the enzyme (Mred). The reduced form then reacts with a second superoxide ion and two protons to form hydrogen peroxide and regenerate the oxidized form of the enzyme

proton-motive force

The proton gradient generated by the oxidation of NADH and FADH

proton motive force equation

Proton-motive force (Δp) = chemical gradient (ΔpH) + charge gradient (ΔΨ)

The proton-motive force powers

the synthesis of ATP

Heterologous experimental systems confirmed that

gradients can power ATP synthesis

the Chemiosmotic Hypothesis

Electron transfer through the respiratory chain leads to the pumping of protons from the matrix to the cytoplasmic side of the inner mitochondrial membrane. The pH gradient and membrane potential constitute a proton-motive force that is used to drive ATP synthesis

Testing the Chemiosmotic Hypothesis

ATP is synthesized when reconstituted membrane vesicles containing bacteriorhodopsin (a light-driven proton pump) and ATP synthase are illuminated. The orientation of ATP synthase in this reconstituted membrane is the reverse of that in the mitochondrion

ATP synthase is made up of

two components, The F1 component contains the active sites and protrudes into the mitochondrial matrix.

ATP synthases bind to one another to form

dimers, which oligomerize.

The oligomers contribute to the formation of

cristae

Each enzyme has

three active sites located on the three β subunits.

The F0 component is embedded in the

inner mitochondrial membrane

The F0 component contains?

the proton channel

The γ subunit connects

the F1 and F0 components

Each β subunit is distinct in that

each subunit interacts differently with the γ subunit.

Structure of ATP Synthase

part of the enzyme complex (the F0 subunit) is embedded in the inner mitochondrial membrane, whereas the remainder (the F1 subunit) resides in the matrix.

Describe how ATP Synthase Assists in the Formation of Cristae

The formation of oligomers of dimers of ATP synthase facilitates the formation of cristae, creating an area where the protons have ready access to the ATP synthase.

The binding-change mechanism accounts for

the synthesis of ATP in response to proton flow.

The three catalytic β subunits of the F1 component can exist in

three conformations

In the O (open) form, nucleotides can

bind to or be released from the β subunit.

In the L (loose) form, nucleotides are

are trapped in the β subunit.

In the T (tight) form, ATP is

synthesized from ADP and Pi

No two subunits are

ever in the same conformation

Each subunit cycles through ____ conformations.

three

The rotation of the γ subunit

interconverts the β subunits

Depict how ATP Synthase Nucleotide-Binding Sites are Not Equivalent

The g subunit passes through the center of the a3b3 hexamer and makes the nucleotide-binding sites in the b subunits distinct from one ano

Why do isolated F1 subunits of ATP synthase catalyze ATP hydrolysis?

It is possible to observe the rotation of the ____ ___directly

t γ subunit

Cloned α3β3γ subunits were attached to

a glass slide that allowed the movement of the γ subunit to be visualized as a result of ATP hydrolysis.