Test 3: ETC and ATP Flashcards
What 3 types of work does a cell do?
- mechanical work
- transport work
- chemical work
What is ATP?
- Adenosine TriPhosphate
- nucleotide with unstable phosphate bonds that the cell hydrolyses for energy to drive endergonic reactions.
What does ATP consist of?
ATP (nucelotide):
- 3 phosphate groups
- ribose
- adenine
How is energy released from ATP?
terminal phosphate bond is hydrolysed:
- inorganic phosphate group (Pi) is removed
- ADP is produced
Explain the strength of phosphate bonds of ATP. Why?
- called “high-energy phosphate bonds”
- weak covalent bonds
- unstable
weak because each phosphate group has a negative charge –> instability due to repulsion
The hydrolysis of ATP is coupled directly to what kind of processes? How?
- endergonic processes
- by transferring the phosphate group to another molecule
What happens when a phosphate group is transferred to another molecule?
the molecule is:
- phosphorylated
- more reactive!
How can ATP be synthesised? By what processes?
- glycolysis
- oxidative phosphorylation
- substrate-level phosphorylation
What is substrate level phosphorylation? How does it occur? What does it form?
- chemical reaction
- forms ATP
- direct transfer and donation of phosphoryl group (-PO32-) to ADP
Where does substrate level phosphorylation occur? Under what conditions?
location: cytoplasm (glycolysis)
conditions: aerobic and anaerobic
What is the primary difference between substrate level phosphorylation and oxidative phosphorylation?
substrate level phosphorylation:
- oxidation and phosphorylation are not joined!
What is oxidative phosphorylation? What does it form? What happens?
- chemical process
- forms ATP
- transfer of electrons from NADH or FADH2 to O2 by a series of electron carriers
What enzyme complexes take part in oxidative phosphorylation?
- ATP synthase
- the electron transport chain
Where does oxidative phosphorylation take place in eukaryotes?
mitochondria
inner mitochondrial membrane: ETC, ATP synthase
mitochondrial matrix: pyruvate dehydrogenase complex, cirtric acid cycle, fatty acid oxidation
What is the ETC?
- set of membrane proteins allowing for oxidative phosphorylation of O2.
- highly exergonic reduction of O2 by NADH and FADH2
- occuring in a number of electron transfer reactions
How is the ETC organized?
4 complexes:
I: NADH-coenzyme Q reductase / NADH dehydrogenase
II: succinate-coenzyme Q reductase / succinate dehydrogenase
III: coenzyme Q reductase
IV: cytochrome C reductase
Where are all of the ETC complexes located?
embedded in the inner mitochondrial membrane
Explain how electrons are carrier (of both NADH and FADH2)
NADH:
I –> II (+ ‘ubiquinone’ coenzyme Q) –> III –> IV
FADH2:
II (+ ‘ubiquinone’ coenzyme Q) –> III
What is ‘ubiquinone’?
‘ubiquinone’ = reduced form of coenzyme Q
Where are FADH2 electrons generated?
in the succinate dehydrogenase (Citric Cycle)
What is an oxidation-reduction couple? State examples.
Pair of molecules of which one is reduced and the other is oxidized.
- lactate & pyruvate
- NADH & NADH+
- FADH2 & FAD
What is complex I? How many electrons does it transfer? From what to what?
NADH-Coenzyme Q reductase / NADH dehydrogenase
- transfers 2 electrons from NADH to coenzyme Q
- contains FMN prosthetic group
- NADH + FMN –> NAD+ +FMNH2
What is complex II? What is it composed of?
- succinate dehydrogenase
- enzyme of the citric acid cycle
- 4 subunits (2Fe-S and 2 FAD)
State the overall reaction for complex II.
succinate + CoQ –> fumarate + CoQH2
What is complex III? What is it composed of?
coenzyme Q-cytochrome c reductase
- passes electrons by the Q-cycle
- 2 b-type cytochromes, 1 c-type cytochrome
What is a cytochrome?
- iron-containing electron transferring proteins
- heme proteins
What do cytochromes undergo?
reduction:
all: Fe3+ –> Fe2+
cytochrome a3: Cu2+ –> Cu+
What is complex IV? What is it composed of?
Cytochrome c oxidase
- a proton pump
- 2 heme centers, cytochrome a, cytochrome a3 and 2 copper proteins
Explain the reaction process with cytochrome IV.
- Cytochrome IV + O2 –> … + 2H2O
- O2 is reduced into H2O
What does the chemiosmotic theory create?
- an electrical gradient (more e- on the outside of the membrane)
- pH gradient (outside is more acidic)
What is Complex V? What does it do?
ATP synthetase / ATPase
- synthesizes ATP through the proton gradient (proton motive force) generated by the ETC
- spontaneous H+ flux
Explain the cycle of ATP-ase. What are the three conformations?
- driven by H+ flow
- conformation of each B subunit changes (as it interacts with the rotating shaft)
loose conformation: active site can bind ADP+Pi
tight conformation: substrates bound and ATP is formed
open conformation: favours ATP release
What would happen if no membrane potential or pH gradient exists?
the reverse reaction would occur:
- ATP hydrolysis
State examples of inhibitors of ATPsynthase. What do they do?
block H+ transport coupled to ATP synthesis / hydrolysis:
- ogliomycin
- DCCD
What is the energetic yield of ETC (oxidative phosphorylation)?
Oxidation of NADH: 3ATP (ADP and Pi)
Oxidation of FADH2: 2ATP (ADP and Pi)
