Chapter 15 The Electron Transport Complex, Oxidative Phosphorylation, and Chemiosmosis Flashcards
Why is oxygen needed to generate energy?
In glycolysis the NADH and pyruvate were considered waste products, both carry energy but in the absence of oxygen we cannot utilize the energy.
What are the two ways ATP is synthesized in our body? Which way is the one where the majority of the ATP is synthesized?
substrate level phosphorylation
Electron Transport Complex, Oxidative Phosphorylation, and Chemiosomosis
Electron Transport Complex, Oxidative Phosphorylation, and Chemiosmosis is how majority of our ATP get synthesized.
Uniport
single molecule moves across membrane
Symport
the movement of one molecule drives the movement of another molecule in the same direction.
Antiport
the movement of one molecule drives the movement of another molecule in the opposite direction
Cotransport
symport and antiport
Active Transport
moving ions or molecules against a concentration gradient which requires an input of energy
Primary Active Transport
energy is used to drive a conformational change.
Secondary Active Transport
energy is used to establish an electrochemical gradient of one molecule.
What is the major difference between the inner and outer mitochondrial membrane?
outer membrane facing the cytoplasm has many transmembrane porin proteins and is highly permeable to many small molecules and ions.
inner membrane is almost completely impermeable to most molecules and ions. Highly selective transporters are needed to cross.
Explain the terms matrix side and cytoplasmic side as they refer to the inner membrane.
Inner membrane is divided into two distinct sides, the side facing the matrix is called the matrix side and the side facing the cytoplasm is called the cytoplasmic side.
Which sides of the inner membrane have a positive vs. negative charge?
The cytoplasmic side has a net positive charge.
The matrix side has a net negative charge.
Mitofusion
fusion of mitochondria
Mitofission
pinch mitochondria into two pieces.
Mitophagy
selective breakdown of mitochondria into its constituent parts
Why are the electrons not directly transferred to oxygen in the electron transport complex?
if the electrons were transferred directly to oxygen, we would be releasing a large amount of energy in one step which would be difficult to capture in one step.
Instead the electron is transferred in multiple steps.
What are the electron carriers used in the ETC?
- NAD+ from dehydrogenases
- FAD/FMN proteins
- The ubiquinones (coenzyme Q)
- Cytochromes
- Iron-sulfur clusters
Which electron carrier of the electron transport complex can move between certain complexes?
cytochrome protein
How can we determine the sequence of the electron pathway in the ETC?
- measure the reduction potentials of each of the components, electrons will go from positive to negative
- Initiate ETC in the absence of oxygen: backlog of ETC, once oxygen is introduced the components closest to oxygen will be oxidized first.
- use of electron transport inhibitors: inhibitor blocks movement of electrons, carriers before block will be reduced, while those after block will be oxidized.
Where is the electron transport chain located?
inner mitochondrial membrane
What are respirasomes?
tightly assembled electron transport complexes.
What lipid is required for a functional ETC?
cardiolipin
What is the function of complex I?
transfer electrons from NADH to the Q pool
pump protons out of the mitochondrial matrix
What is the Q pool?
preexisting pool of fully reduced (QH2) and fully oxidized quinones (Q).
What is the proton count at the end of complex I?
4 protons are carried across the membrane from pump, 2 protons went to Q pool, 1 proton gained from NAD+.
What is the adaptor role of FMN in complex I?
Iron sulfur cluster can accept one electron at a time
NADH must drop 2 electrons at a time
FMN can transfer either one or two electrons serving as an adaptor between Fe-S clusters and NADH.
What is the electron donor and the electron acceptor in complex I?
Electron donor: NADH
Electron acceptor: FMN accepts electrons and passes it along a series of Fe-S clusters until finally the electrons are passed onto Q to make QH2 and rejoins the Q-pool
Which complex is shared with the citric acid cycle?
Complex II, it is the succinate dehydrogenase from the citric acid cycle.
What is the electron donor of complex II?
FADH2
What is the electron acceptor of complex II?
oxidized quinone from Q pool
How many protons are pumped from complex II?
no protons are pumped from complex II
Are electrons from complex II worth as many ATP molecules as electrons that entered the ETC in complex I?
No, because the electrons from FADH2 have bypassed complex I. They pump fewer protons and do not generate as much ATP as those originating on NADH.
What is the purpose of the heme group in complex II?
acts as a protective gate to prevent electrons from leaking out of complex II
What is the function of complex III of the electron transport complex?
transferring electrons from the Q-pool to another electron carrier, cytochrome c, and pumping protons.
What is the Q cycle?
mechanism of how electrons can move from complex I and II to complex III
Which complex does the Q cycle happen?
Complex III
How many protons are pumped from complex III?
4 protons
Describe the Q cycle
- A QH2 docks onto first site of complex III. One electron is transferred to cytochrome c another electron is transferred to Q forming Q dot.
(The cytochrome c leaves the complex and Q goes into Q pool). 2 protons are pumped in this process.
- A QH2 docks onto first site, one electron is transferred to a new cytochrome c and the other electron is transferred to Q dot forming QH2.
(The cytochrome c leaves the complex, Q and QH2 go back into Q pool). 2 protons are pumped in this process.
What is the function of complex IV?
the cytochrome c drops off the electron here, where it will be used to reduce oxygen to water.
What are the steps of complex IV of the electron transport complex?
- 2 cytochrome c sequentially transfer their electrons to copper and heme.
- The copper (II) is reduced to copper (I)
The iron (III) in heme is reduced to iron (II). - The oxygen binds forming a peroxide bridge.
- 2 cytochrome c and 2 protons cleave the peroxide bridge.
- Addition of two more protons release water.
What is the net proton count on the N side and P side after complex IV?
N side net depletion of 8 protons
P side grows by 4 protons.
What is the net proton count for complex IV?
4 chemical protons
2 pumped protons
How many protons are pumped per NADH?
10 protons
How many protons are pumped to complete the electron transport complex?
12 protons
How many protons are pumped per cytochrome c in complex IV?
1 proton per cytochrome c
How many NADH molecules are required to complete all the steps of complex IV?
2 NADH molecules (4 electrons)
What force is ATP synthesis driven by?
Proton motive force
What are the two parameters for the proton motive force?
chemical potential: change in pH (inside alkaline)
electrical potential: change in electrical gradient (inside negative)
What are uncouplers?
discharge the proton gradient, short circuiting synthesis of ATP by the ETC.
ETC can continue to function but no ATP is made.
What is the enzyme that synthesizes ATP?
The ATP synthase
Describe the structure of the ATP synthase
ATP synthase consists of multiple polypeptide chains, has two major components the F1 and Fo.
In what subunit of ATP synthase is the active site for ATP synthesis found?
beta subunit
How many active sites are present per complex in the ATP synthase?
3 active sites per complex
What is unusual about the structures of the beta subunits?
beta subunits are constantly changing their conformation as a result of the gamma subunit rotating which facilitates the binding and release of ATP.
What is the thermodynamically unusual feature of the ATP synthase enzyme?
ATP synthase is bound to ATP standard free energy is zero.
Enzymes are not supposed to bind to products tightly, and enzymes are not supposed to change the equilibrium constant.
How does the thermodynamically unusual feature of the ATP synthase enzyme contribute to ATP synthesis?
since the enzyme binds to the product with a higher affinity than reactants, this shifts equilibrium substantially.
What is the energy in the proton gradient used for in the ATP synthase?
protons from gradient will flow through the Fo subunit causing the c subunits to rotate.
epsilon and gamma subunits are linked to the c subunit which causes the rotation of the gamma subunit which induces conformational changes in the beta subunits of the F1 domain.
What makes the ATP synthase a-subunit channel an unusual proton channel?
it is a one sided directed proton channel, protons go in but can’t come out.
alpha subunit open on one side but not on the other side.
How many ATP are being made at one time by the ATP synthase?
3 ATP
What is the binding change model of ATP synthesis?
gamma subunit rotates beta subunit
three different conformations: open, loose, tense
the subunits move in this order open, loose, loose, tense, tense, open
What binds to the open conformation of the beta subunit?
ADP, Pi, and ATP can reversibly bind to open conformation of the beta subunit.
What binds to the loose conformation of the beta subunit?
binds ADP and Pi.
What binds to the tense conformation of the the beta subunit?
binds tightly to ATP.
How is the ATP synthase mechanism distinct?
involves conformational changes of the beta subunits and relies on a pre-existing proton gradient.
What is the energy of the proton gradient needed for in ATP synthase?
to kick the ATP off of the synthase, it is for the transition from the tense state to the open state.
Why does the import of precursors for ATP synthesis deplete the proton gradient used for ATP synthesis?
Pi imported in the form of H2PO4, reduces size of the proton gradient
ADP imported into membrane by an antiporter with ATP. Reduces amount of energy available in the membrane to synthesize ATP.
What is the glycerol-3-phosphate shuttle?
In skeletal muscle and brain, NADH equivalents from glycolysis enter into the matrix via the glycerol-3-phosphate shuttle.
What is happening in the glycerol-3-phosphate shuttle?
On the cytoplasmic side of mitochondrial membrane the glycerol-3-phosphate is oxidized to dihydroxyacetone phosphate by FAD.
FADH2 goes into Q-pool
Why do we need the glycerol-3-phosphate shuttle?
NADH made in glycolysis is synthesized in the cytoplasm, only matrix generated NADH can feed electrons into the ETC.
What is the proton count in glycerol-phosphate shuttle?
These electrons bypass complex I, generate 6 protons.
What is the malate shuttle?
it is used in the liver, kidney, and heart to move cytoplasmic NADH electrons into the matrix.
What are the two rings of the malate shuttle?
The outer ring and the inner ring.
Outer ring: moves electrons
Inner ring: balances out the atoms
What is the process used by the malate shuttle?
Electrons from NADH are used to reduce oxaloacetate to malate.
Malate enters the mitochondria where it is oxidized back to oxaloacetate.
Oxaloacetate has to be moved back across the membrane so it can be used again.
Transaminase converts oxaloacetate to aspartate.
Aspartate leaves matrix.
Aspartate converted back to oxaloacetate.
Does the malate shuttle affect the proton count?
No
What is the major form of regulation of oxidative phosphorylation?
when ratio of ATP/ADP is high, OP reduced.
when ratio of ATP/ADP low, OP increases.
What is the AMPK kinase?
activated under high concentrations of AMP.
Explain activation of AMPK
- One ADP transfers a phosphate to another ADP producing AMP and ATP.
- High conc of AMP activates AMPK.
- AMPK adds phosphorous groups activating proteins which increases energy status of cell.
What are the consequences of AMPK activation?
stimulates glycolysis, stimulates breakdown of fats, inhibits gluconeogenesis.
