01: Oxidative Phosphorylation and Role of the Electron Transport Chain

Structure of Mitochondrial Membranes: Outer Membrane

• Relatively permeable to small molecules and ions due to _____

• is a voltage-gated anion channel

• forms pores across the membrane

• transport occur

• Allows _____ molecules to pass through

porin, anionic

Structure of Mitochondrial Membranes: Inner Membrane

• impermeable to most small molecules and ions

• Water, gases such as CO2 and O2 can pass through

• Metabolites, phosphate, protons, etc. can also pass through

• Transport of other molecules requires specific transporters

• Multiple folds to increase the surface area called _____

cristae

_____ is the most important part of mitochondria

• Contains major and important metabolic enzymes

• Enzymes for TCA cycle, fatty acid oxidation

• also contains genetic materials

  • needed to synthesize key mitochondrial proteins, including enzymes

Matrix

Electron Transport Chain (ETC) is bound to the ____

inner membrane

Respiratory complex

• NADH and FADH2 transfer their electrons to molecular O2 through a series of redox reactions in a process called _____

• molecular oxygen is vital to the process

respiration

Respiratory complex

• Redox reactions are catalyzed by membrane-embedded enzymes

  Respiratory complexes and auxiliary proteins together comprise the _____

  • aka the _____

respiratory chain, Electron Transport Chain

Respiratory chain = series of electron carriers

• Dehydrogenases collect electrons from catabolic pathways and then

• Funnel them into universal electron acceptors

• ______ (NAD+ or NADP+)

• _______ (FMN or FAD)

Nicotinamide nucleotides, Flavin nucleotides

_______ catalyze reversible reactions between the oxidized and reduced forms of NAD(P)+

Two hydrogen atoms are removed from the substrates:

• One is transferred as a hydride ion (:H-) to NAD(P)+

• One is released as H+

Nicotinamide nucleotide-linked dehydrogenases

_________ = contain a very tightly, sometimes covalently, bound flavin nucleotide (FMN or FAD)

Flavoproteins

The oxidized flavin nucleotide can accept either:

• One electron (yielding ________) or

• Two electrons (yielding ______)

the semiquinone form, FADH2 or FMNH2

Coenzyme Q, Ubiquinone, Q

• a lipid-soluble benzoquinone with a long isoprenoid side chain

• Ubiquitous in cells

• ______ structure

• QH2 is the reduced dihydro form

• The structures of Q and QH2 allows 1 and 2 electron- transfers to electron acceptors

• Coenzyme Q is a redox participant in the electron transport chain

• Freely diffusible within the inner mitochondrial membrane

• Plays a central role in coupling electron flow to proton movement

Quinone

_____ is a redox participant in the electron transport chain

Coenzyme Q

Tightly bound prosthetic groups

Participate in electron transfer

Involves Fe(II) and Fe (III)

Mechanism of how the electrons pass to and from heme groups is unclear

Heme groups

______ = proteins with characteristic strong absorption of visible light due to their iron-containing heme prosthetic groups

• One-electron carriers

• 3 classes in mitochondria: a, b, and c

• Hemes of a and b are not covalently bound to associated proteins

• c is covalently attached through Cys residues

Cytochromes

the c family in cytochromes are bound to ____ resides

Cysteine (Cys, C)

______= proteins that contain iron in association with inorganic sulfur atoms and/or with the sulfur atoms of Cys residues in the protein

• participate in one-electron transfers

• Non-heme iron complexes

• Found in membrane-bound enzymes and soluble enzymes

iron-sulfur proteins

Fe-S clusters help stabilize the enzyme structure and protect it against ______ attack

proteolytic

ETC contains four multi-subunit enzyme complexes

• Complex I: _____

NADH-Q reductase

ETC contains four multi-subunit enzyme complexes

• Complex II: ____

Succinate-Q reductase

ETC contains four multi-subunit enzyme complexes

• Complex III: _________

QH2-cytochrome c reductase

ETC contains four multi-subunit enzyme complexes

• Complex IV: ______

Cytochrome c oxidase

Complex I: NADH-Q reductase

• Flavoprotein that uses ______

• Contains non-heme iron centers(Fe-S complexes)

• 2 electrons from NADH are transferred via _____ to coenzyme Q

• For every 2 electrons of NADHtransferred,

  • 4 H+ are pushed out of the matrix into the inter-membrane space

  • NADH + H+ + Q → NAD+ + QH2

FMN

Complex II*: Succinate-Q reductase

• couples the _____ of succinate withthe ____ of ubiquinone

• also functions to convert succinate to fumarate in the citric acid cycle

• Transfers electrons → Does not act as a proton pump

• Contains FAD, heme molecules, Fe-S centers, and cyt b

• Succinate is oxidized to fumarate

  • FAD is reduced to FADH2

  • FADH2 re-oxidized to FAD and re-enters Krebs cycle

• Coenzyme Q is reduced

oxidation, reduction

Complex III: QH2-cytochrome c reductase

• Couples the transfer of 2 electrons from ubiquinol to cytochrome c

• Contains cyt b, cyt c and Fe-Scenter

• Acts as a ______

• For every molecule of QH2 converted to Coenzyme Q

• 4 H+ are pushed out of the matrix into the inter-membrane space

• Electrons are passed one at a time from QH2 to two successive molecules of cyt c

proton pump

Complex IV: Cytochrome c oxidase

• Contains cyt a, cyt a3 and two Cu ions

• Carries electrons from cyt c to molecular oxygen, reducing it to H2O

• ______ is the final electron acceptor

• ______ is the final product

O2. Water

_______ = transmembrane differences in proton concentration are the reservoir for the energy extracted from biological oxidation reactions

chemiosmotic theory

_______ is the movement of ions across a semipermeable membrane bound structure, down their electrochemical gradient

Chemiosmosis

ConcH+ (outside) >> ConcH+ (inside) : _____ gradient

concentration

Chargee- (outside) >> Chargee- (inside) : ____ gradient

potential

_____ catalyzes the formation of ATP i.e. energy!

ATP synthase

Complex V: ____

ATP synthase

____ drives the synthesis of ATP from ADP and Pi, as protons flow passively back into the matrix through its proton pore

ATP synthase

For Complex V

• ____ domain is located on the matrix side of the inner membrane

F1

For Complex V

• ____ domain spans the inner membrane

F0

Chemiosmotic model

• _____ H+ enter the inter-membrane space, and ______ H+ re-enters the matrix

10, 4

Complexes_____are transmembrane proteins

I, III, and IV

Complex I, III, and IV are also ______ that push H+ to the inter-membrane space

proton pumps

______ is on the inner surface of the inner membrane

Complex II

_____ is not a proton pump

Complex II

In ______, 4 H+ are ejected for every molecule of O2 that accepts the e- (O2 is the final acceptor)

complex IV

Complex V or _____ is a distinct protein complex

• It is not a part of the other four complexes

ATP synthase

ATP synthesis by the _______ is accompanied by H+ re-entry into the matrix

F0-F1 domains of ATP synthase

3 H+ re-enter from____, and one H+ is imported along with ______

• Net 4 H+ re-enter

ATP synthase, inorganic phosphate

ATP from ____ = 10/4 = 2.5 ATP (rounded to 3 ATP)

ATP from ____ = 6/4= 1.5 ATP (rounded to 2 ATP)

NADH, FADH2