Oxidative Phosphorylation

Question 1

Two Purposes for Catabolic Pathways

Answer 1

Breakdown of larger molecules into smaller building units 
Release and (temporary) storage of energy in high-energy molecules

Question 2

Are Catabolic Pathways Reductive or Oxidative

Answer 2

Oxidative: metabolites are oxidized as cofactors are reduced

Reoxodidation of cofactors are used to generate ATP

Question 3

Oxidation in Oxidative Phosphorylation

Answer 3

Oxidation of reduced cofactors (NADH, FADH2) and reduction of molecular oxygen

Question 4

Phosphorylation in Oxidative Phosphorylation

Answer 4

Phosphorylation of ADP to ATP

Question 5

Where does Oxidative Phosphorylation Occur

Answer 5

Inner mitochondrial membrane

Question 6

Cofactors in Oxidative Phosphorylation

Answer 6

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

Question 7

Coenzyme Q

Answer 7

Lipid-soluble molecule

Transports electrons to complex 3 from complexes 1 and 2 in the inner mitochondrial membrane

Question 8

The Electron Transport Chain

Answer 8

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)

Question 9

What is the terminal electron acceptor?

Answer 9

Oxygen: has a very high reduction potential

Question 10

Draw the path of electrons from NADH through the electron transport chain

Answer 10

Check cheat sheet

Question 11

Complex 2

Answer 11

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

Question 12

The path of electrons from FADH2

Answer 12

Check cheat sheet

Question 13

The Proton Electrochemical Gradient

Answer 13

The potential energy of the H+ gradient is converted to the chemical energy in the phosphoanhydride bonds of ATP

Question 14

ATP Synthase

Answer 14

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

Question 15

Fo

Answer 15

Transmembrane portion
Protons pass through
Triggers conformational change in F1

Question 16

F1

Answer 16

Catalytic portion

Synthesis of ATP from ADP and Pi

Question 17

The Coupling of Oxidation and Phosphorylation

Answer 17

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

Question 18

The P:O Ratio

Answer 18

The amount of ATP made per oxygen atom reduced to water

Question 19

How is the rate of oxidative phosphorylation related to the relative concentration of ADP?

Answer 19

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

Question 20

Low energy use

Answer 20

Low [ADP] = low ATP synthesis which means that O2 consumption drops and the CAC and PDH are inhibited

Question 21

High energy use

Answer 21

High [ADP] = ATP synthesis which means that O2 consumption increases and the CAC and PDH are activated

Question 22

Uncoupled systems

Answer 22

Allows protons to enter the matrix without ATP synthesis

Protons may enter the matrix through a separate process, generating heat instead of ATP

Question 23

Brown Adipose Tissue

Answer 23

Mammals sometimes uncouple oxidative phosphorylation to deliberately generate heat

Question 24

What does it mean when oxygen consumption increases in the presence of an uncoupler

Answer 24

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