1.09 - Oxidative Phosphorylation Flashcards
What are the three structural components of ATP?
Adenine
Ribose
Triphosphate with phosphoanhydride bonds
Describe the kinetics of ATP Synthesis
The reaction requires considerable energy input (30kJ/mol)
Cells couple reactions to facilitate the synthesis, e.g. to a reaction with deltaG makes the reaction more favourable
Describe Substrate Level phosphorylation
Coupling ATP synthesis to Creatinine Phosphate–>Creatinine renders the reaction favourable.
Phosphate is transferred from CrP to ADP –> ATP
Rapid response for ATP generation
Used (initially) during strenuous exercise and CrP is replenished during rest
However, an inefficient process –> one mole of ATP per mole of Pi donor.
What method have cells devised to overcome the inefficiency of substrate level phosphorylation?
Oxidative Phosphorylation
Describe the funnelling of metabolites to mitochondria
Major site of ATP synthesis is the mitochondrial matrix
Primary anabolic sites are cytosolic
FA’s enter the mitochondria via the carnitine shuttle system
Carbohydrates provide pyruvate –> Acetyl CoA
Destination for metabolic fuels is the TCA Cycle
Entry to the TCA cycle is via AcetylCoA
What are the energy products of the TCA Cycle?
NADH & FADH2
Describe the basic concepts of Oxidative Phosphorylation
The culmination of catabolic metabolism
Generation of high amounts of ATP
Reduction of O2 to H2O using electrons from NADH & FADH2
Occurs on the inner mitochondrial membrane
Involves a series of “downhill” electron transfers (i.e. exergonic)
Energy used to drive protons through the inner membrane, they don’t like to go across the membrane due to positive charge
Transmembrane chemical & electrical difference of the proton gradient drives ATP synthesis
Describe the Electron Transport Chain
The ETC converts energy from redox reactions to a proton gradient
The ETC comprises integral and peripheral membrane proteins at the inner mitochondrial membrane
- Four membrane bound multiprotein complexes (I-IV)
- 2 membranous “carriers” move electrons between complexes
Describe the steps in the ETC
Complexes I,III & IV transport H+ from the inner mitochondrial matrix in to the inter membrane space, creating a proton gradient across the membrane
NADH donates electrons to complex I forming NAD+
Complex II is part of the TCA cycle and does not transport H+
Electrons enter complex II from the reaction succinate + FAD –> Fumerate + FADH2
Mobile, membranous “carriers” move electrons between complexes
- Ubiquinone (UQ) moves electrons from complexes I and II to III
- Cytochrome C (cyt c) moves electrons from complex III to IV
Complex IV produces H20 from oxygen using electrons from Cyt C, and in doing so moves 4H+ out of the matrix
Describe the proton gradient formed by the electron transport chain
The ETC moves protons out of the inner mitochondrial matrix in to the inter membrane space. This creates a concentration and electrical gradient across the membrane.
The H+ want to move in to the matrix to equalise their concentration and the electrical gradient wants to equalise.
This is an unstable situation
“The movement of protons back across the membrane could be utilised in ATP synthesis”
What structure couples the movement of protons to synthesise ATP
ATP Synthase
What are the three distinct units of ATP Synthase?
Membrane bound unit (F0)
Rotor unit
ATP synthesis unit (F1)
The rotor and synthesis unit are located in the inner mitochondrial matrix
Describe the ATP synthesis unit of ATP synthase
3 sites of nucleotide binding with high, medium and low affinity for the nucleotide
Describe the Membrane bound unit of ATP Synthase
Membrane bound
Multiple protein subunits
Proton channel
Describe the efficiency but poor location of ATP synthesis
ATP synthesis occurs in the mitochondrial matrix, but ATP is mainly required in the cytosol
However, ATP does no cross membranes
ATP synthesis requires ADP in the mitochondrial matrix
