Oxidative Phosphorylation Flashcards
Two Purposes for Catabolic Pathways
Breakdown of larger molecules into smaller building units Release and (temporary) storage of energy in high-energy molecules
Are Catabolic Pathways Reductive or Oxidative
Oxidative: metabolites are oxidized as cofactors are reduced
Reoxodidation of cofactors are used to generate ATP
Oxidation in Oxidative Phosphorylation
Oxidation of reduced cofactors (NADH, FADH2) and reduction of molecular oxygen
Phosphorylation in Oxidative Phosphorylation
Phosphorylation of ADP to ATP
Where does Oxidative Phosphorylation Occur
Inner mitochondrial membrane
Cofactors in Oxidative Phosphorylation
Multiple cofactors are reversibly oxidized/reduced during electron transport
-FMN, iron-sulfur clusters, Cu++, cytochrome heme groups (prosthetic groups)
-Coenzyme Q (lipid-soluble cofactor)
Each cofactor has a characteristic reduction potential or affinity for electrons
-electrons move from cofactors with lower reduction potential to those with higher reduction potentials
Coenzyme Q
Lipid-soluble molecule
Transports electrons to complex 3 from complexes 1 and 2 in the inner mitochondrial membrane
The Electron Transport Chain
Redox reactions have a free energy change related to reduction potential
-reduction potential is an affinity for electrons
-higher reduction potential = more negative deltaG
Free energy changes from redox reactions can be used to transport protons across the membrane (primary active transport)
What is the terminal electron acceptor?
Oxygen: has a very high reduction potential
Draw the path of electrons from NADH through the electron transport chain
Check cheat sheet
Complex 2
Succinate dehydrogenase
An integral membrane protein, complex 2 contains FAD as a prosthetic group
Catalyzes the oxidation of succinate to fumarate as part of the citric acid cycle
Electrons from succinate are ultimately transferred to coenzyme Q in the membrane
No protons are moved across the membrane at complex 2
The path of electrons from FADH2
Check cheat sheet
The Proton Electrochemical Gradient
The potential energy of the H+ gradient is converted to the chemical energy in the phosphoanhydride bonds of ATP
ATP Synthase
2 portions
-Fo
-F1
It is the rate of ATP synthesis that determines proton movement and ultimately oxygen consumption
Every complete turn of the central shaft is associated with the generation of 3 ATP
Fo
Transmembrane portion
Protons pass through
Triggers conformational change in F1
F1
Catalytic portion
Synthesis of ATP from ADP and Pi
The Coupling of Oxidation and Phosphorylation
The rates of reoxidation of NADH, of electron transport, and of oxygen consumption are coupled to the rate of consumption (and synthesis) of ATP through the magnitude of the H+ electrochemical gradient
The P:O Ratio
The amount of ATP made per oxygen atom reduced to water
How is the rate of oxidative phosphorylation related to the relative concentration of ADP?
O2 consumption is connected to ATP production at the ATP synthase
Oxygen consumption increases when ADP concentration rises
ADP concentration reflects the energy-consumption of the cell
Low energy use
Low [ADP] = low ATP synthesis which means that O2 consumption drops and the CAC and PDH are inhibited
High energy use
High [ADP] = ATP synthesis which means that O2 consumption increases and the CAC and PDH are activated
Uncoupled systems
Allows protons to enter the matrix without ATP synthesis
Protons may enter the matrix through a separate process, generating heat instead of ATP
Brown Adipose Tissue
Mammals sometimes uncouple oxidative phosphorylation to deliberately generate heat
What does it mean when oxygen consumption increases in the presence of an uncoupler
This refers to situations when electron transport occurs without ATP synthesis (and thus, also, when catabolism of fuel molecules occurs without ATP synthesis)
The proton gradient is then dissipated faster, and the rate of electron transport increases. The rate of reoxidation of reduced electron carriers increases,, and the rate of reactions in the citric acid cycle increases
