Terminal respiration IA% (+ Flashcards
1
Q
Diagram summary 1
A
2
Q
Diagram summary 2
A
3
Q
Mitochondria
A
- The only site of oxidative phosphorylation in eukaryotes
- Allows the coupling of the oxidation of carbon fuels to ATP synthesis
- Utilises proton gradients to produce ATP (and lots of it)
4
Q
Locations
A
- For oxidation in the terminal respiratory system of eukaryotic cells, NADH and FADH2 have to be in the mitochondrial matrix
- The majority of NADH and FADH2 is formed there, already (citric acid cycle and β-oxidation of fatty acids), but some NADH is formed in the cytoplasm (gycolysis)
- A shuttle is used to move reducing equivalents across the mitochondrial membrane
- Cytoplasmic NADH cannot cross the membrane, but FADH2 can pass it’s e-’s on to the electron transport chain within the mitochondria: ‘Glycerol phosphate shuttle’
5
Q
Glycerol phosphate shuttle
A
- The NADH is unable to cross the membranes of the mitochondria, but Glycerol-3-P can, passing it’s e-’s to FADH2
- Oxidation of FADH2 in the electron transport chain generates, per mol, less ATP than oxidation of NADH
- Thus, an energetic ‘price’ is paid for using cytosolic reduced co-substrates in terminal respiration
6
Q
The electron transport chain
A
- Complex I: NADH-Q oxidoreductase
- Complex II: Succinate-Q reductase
- Complex III: Q- cytochrome c oxidoreductase
- Complex IV: Cytochrome c oxidase
7
Q
Complex I: NADH-Q oxidoreductase
A
•Oxidises NADH and passes the e-’s to ubiquinone to give ubiquinol (QH2) = reduced ubiquinone
Ubiquinone + e-‘s ⇒ Ubiquionol
- Utilises Fe-S centres and FMN (flavin mononuleotide)
- Pumps H+ ions into the intermembrane space
8
Q
Complex II: Succinate-Q reductase
A
- Oxidises FADH2 and like complex I passes high-energy e-’s to ubiquinone, which becomes ubiquinol (QH2)
Ubiquinone + e-‘s ⇒ Ubiquionol
- Utilises Fe-S centres to channel e-’s
9
Q
•Complex III: Q- cytochrome c oxidoreductase
A
- Takes the e-’s from ubiquinol (QH2) and passes them to cytochrome c
- 1 QH2 is oxidised to yield 2 reduced cytochrome c molecules
- Pumps H+ into the intermembrane space
10
Q
•Complex IV: Cytochrome c oxidase
A
- Takes the e-’s from cytochrome c and passes them to molecular O2
- e-’s channelled through Fe-Cu centre
- Pumps H<strong>+</strong> into the intermembrane space
11
Q
Electron flow
A
- Energy is conserved from the breakdown of food molecules and ultimately leads to the oxidation of NADH, FADH2, ubiquinone and cytochrome c
- Energy is further conserved through the setting up of a proton gradient across the inner mitochondrial membrane
12
Q
Chemiosmosis and proton-motive force
A
- As e-’s pass through the complexes of the transport chain, protons move from the matrix to the outside of the inner mitochondrial membrane – chemiosmosis
- This movement has particular spatial directionality, so is classed as ‘vectoral’
- This is an example of an energy transformation
- The protons on the outside of the membrane act as a store of potential energy
- When these protons are ‘allowed’ to flow back down their gradient they release energy to do work – proton motive force
13
Q
ATP Synthesis
A
- Protons eventually flow down their concentration gradient, back into the matrix of the mitochondria
- Only a relatively small number of sites exist on the membrane were this happens
- At these sites a large multi-unit protein complex called ATP synthase (ATPase for short) is found
- ATPase has a mechanism that allows protons to pass through
- As they flow through ATPase, the energy stored in the gradient is used to convert ADP + Pi ⇒ ATP
- ATP then takes this potential energy to do work in the cells of the body
- This is the final step in metabolising the food molecules we eat into energy
14
Q
The stoichiometry of oxidative phosphorylation
A
- Oxidation of FADH2 in the terminal respiration system generates less ATP than NADH oxidation
- As e-’s pass through the electron transport chain, complexes I, III and IV move a total of 8 H<strong>+</strong> from the matrix to the outside of the membrane
- ATP synthase can produce 1 ATP for every 3 H+ it moves back into the matrix across the membrane
- NADH feeds in e-’s at Complex I, which means the e-’s pass through all 3 sites in the chain that allow protons to move across the membrane (Complexes I, III and IV)►
- FADH2 feeds in at Complex II, so only 2 of the sites that move protons across the membrane are utilised (Complexes III and IV)
- Stoichiometrically, approximately 2.5 and 1.5 mol of ATP are generated per mol of NADH and FADH2 respectively
15
Q
Diagram summary 3
A
- The food molecules are completely broken down to CO2 and H2O
- Some potential energy from food molecules is ‘saved’, after being transformed through reduced co-reactants and the terminal respiratory system, and is used to make ATP
16
Q
Coupling and uncoupling
A
- Electron transport is said to be coupled to ATP synthesis
- If the inner mitochondrial membrane becomes permeable to protons, the proton gradient cannot be generated
- If this happens the electron transport can still occur, with O2 being reduced to H2O, but no ATP is made
- The two processes are now uncoupled
- The energy released from e-’s passing along the terminal respiration system does not make ATP, and is released as heat
- Malignant hyperthermia is a disease caused by ‘leaky’ mitochondrial membranes that uncouple electron transport and ATP synthase
17
Q
ATP synthase
A
Has 2 parts:
•F0 – membrane bound proton conducting unit
–10 subunits
–Separate subunit connects F0 to F1
•F1 – protrudes into the mitochondrial matrix and acts as the catalyst for ATP synthesis
–Produces lots of ATP from the proton motive force energy collected by F0
