Electron Transfer and Oxidative Phosphorylation

What are the main reducing fuels for the cell

carbohydrates lipids and amino acids

what are electrons form reduced fuels transferred to

they are transferred to the reduced cofactors NADH or FADH2

what energy is used to make ATP in oxidative phosphorylation

energy from NADH and FADH2 is used to make it

what does the cell produce for every molecule of glucose that is oxidized

it produces 6CO2- which is disposed when you exhale, 4 ATP for fuel, 10 NADH and 2 FADH2

what do redox reactions do

they get the energy out of glucose to create ATP

Why is the production of ATP from ADP and Pi highly unfavorable, what is the delta G”

it is unfavorable because the phosphate groups are highly electronegative and do not want to be in close proximity in a single molecule. The delta G’ is -33.8kJ/mol

how does ATP store energy

the phosphate bonds in ATP have high chemical energy and their close together negative charges act like a clamped spring, once they break, the energy from the broken bonds can be used to offset the cost of energy requiring reactions

When is NADH oxidized

it is oxidized when combined with the inner membrane of mitochondria, in prokaryotes it is oxidized in the plasma membrane

what do the molecules in the inner mitochondrial membrane cycle between

they cycle between oxidized and reduced states

which pathway of cellular respiration is the electron transport chain

it is the 4th pathway

what happens during the electron transport chain

the electrons are transported through a series of integral membrane proteins within the inner mitochondrial membrane

how is energy released as electrons move through the ETC

it is released through a series of thermodynamically favorable redox reactions within the proteins

what is the energy released during the ETC used for

it is used to pump protons across the inner membrane into the inter membrane space

what does the energy released during the ETC form

it forms an electrochemical gradient in H+ ions across the inner mitochondrial membrane

what is most of the chemical energy from glucose accounted by during the ETC

it is accounted by a proton electrochemical gradient

what is the delta G’ during the ETC as electrons flow down the energy gradient from NADH to O2

it is highly exergonic, delta G’=-220KJ/mol of NADH

what protein complexes catalyze the flow of electron during the ETC

Complex 1: NADH-Q (ubiquinone) oxydoreductase

Complex 2: Succinate-Q reductase

Complex 3: Q-cytochrome C oxiodoreductase

Complex 4: Cytochrome C oxidase

what do the complexes of the ETC have the ability to accept

they all have different abilities to accept electrons. Some only except electrons while other accept electrons and protons. this leads to a reception potential E

What happens as electrons move from one molecule to another in the ETC

they will be held more tightly, smaller amount of energy is released in each reaction and each successive bond hold less potential energy

how does O2 enter the mitochondrial matrix

it enters by diffusion through the inner mitochondrial membrane since gas can generally freely diffuse across lipid bilayers

what is E’

it is the relative affinity for electrons in the electron acceptor

when does E’ increase

it increases as electrons are transported along the ETC

what kind of E’ is more likely to be reduced

a larger and positive one

what is NADH-Q oxioreductase comprised of

it is comprised of NADH dehydrogenase, flavin, mono nucleotide, iron-sulfur clusters and ubiquinone

what does NADH-Q oxiodoreductase do

it will oxidize NADH which will donate a hydride ion and 2 electrons to FMN which is reduced into FMNH2. the NAD+ will be reduced through the citric acid cycle. 2 electrons are transferred to Fe-S clusters to Q and Q is fully reduced into QH2

what type of reaction is an NADH-Q oxioreductase reaction

it is an exergonic reaction and provides energy to power the next reaction

how many H+ ions doe NADH-Q oxioreductase pump

it pumps 4 H+ ions across the membrane from the matrix into the intercellular space

what is Succinate-Q reductase comprised of

it is comprised of succinate dehydrogenase, FAD, and iron sulfur clusters

what does succinate-Q reductase do

it accepts electrons from succinate (TCA cycle) and acts as a second entry point to the ETC

what happens when succinate is oxidized into fumarate

2 electrons are accepted by FAD and become reduced into FADH2 and 2 electrons pass to Fe-S clusters and to Q. There is no pumping of H+ ions

what is oxidation of FADH2 into FAD coupled with

it is coupled with the reduction of Q into QH2

where can FAD be reduced

it can be reduced in the TCA cycle

what is Q-cytochrom C oxioreductase compromised of

it is compromised of cytochrome b ( 2 Fe-heme), Rieske subunits (2 Fe-S clusters) and cytochrome c1 proteins (fe-heme)

where does Q-cytochrome C oxiodoreductase transfer electrons

it transfer electrons from the QH2 to cut c

how many electrons can cyt c accept at a time

is can only accept one at a time

what happens during the first step (first half-cycle) of the Q cycle in Q cytochrome C oxidoreductase

QH2 and Q binds to 2 different sites

QH2 transfers the first election to Rieske center (Fe-S), cyt c1 and the cyt c

QH2 transfers the second electron to cyt b and then to Q bound at the other site

2H+ ions are released into the inter membrane space

QH2 is oxidized to Q and dissociates from the complex

Q bound at the second site enters a transitional QH- radical state (semiquinone)

what happens during the second step (2d half cycle) of the Q cycle in Q-cytochrome C oxidoreductase

repeat of step 1

new QH2 binds to the first site and transfers 2 electrons

1 electron passes to cytochrom c

1 electron passes to cytochrome b, reducing QH- to QH2 before it dissociates from complex 3 and can be recycled

2 more H+ ions released

how many H+ are pumped at the end of a full Q cycle

4 H+ are pumped from the matrix to the intercellular space for the 2 electrons transferred from each of QH2 at the end

what is cytochrome C oxidase composed of

it is composed of cyt a and a3 (heme) groups and copper groups (CuA/cuA and CuB)

what does cytochrome C oxidase do

it oxidizes the reduced cyt c

transfers electrons to oxygen as the final electron accepto

takes out 2 H+ from the matrix to become water

2 additional H+ are pumped out of the matrix as the electrons move through complex IV

how many molecules of cytochrome c are required to produce one molecule of H2O

2 molecules are required

what does the difference in number of protons transported reflect

it reflects differences in ATP synthesized

what helps reduce the concentration of H+ in the matrix

the direct pumping of hydrogen ions and the uptake of hydrogen for reactions within the ETC

after one complete cycle of cellular respiration how much NADH and FADH2 does glucose generate

it generates 10 molecules of NADH and 2 molecules of FADH2

what are the net products formed during the oxidation of one acetylCoA via the citric acid cycle

3 NADH 1 FADH2 and 1 GTP are formed

which enzyme is involved in the citric acid cycle and the ETC

succinate dehydrogenase is involved in both

how many ubiquinol are oxidized during the Q cycle

2 of them are oxidized during the Q cycle

what does the movement of electrons down the ETC drive

it drives the formation of a proton gradient

what is the energy released by electron transport used for

it is used to transport protons against the electrochemical gradient

what is them energy needed to phosphorylate ADP provided by

it is provided by the flow of protons down the electrochemical gradient (chemiosmosis)

what are the steps of the chemiosomtic theory

1. the reduced substrate (fuel) donated electrons

2. the electron carriers pump H+ out as electrons flow to O2

3. energy of electron flow is stored as electrochemical potential

4. ATP synthase uses electrochemical potential to synthesize ATP

where can the proton gradient needed for ATP synthesis be stably established

it can be stably established across a membrane that is impermeable to ions like the inner membrane in mitochondria

what must a membrane for chemiosmotic energy coupling contain

it must contain proteins that couple the downhill flow of electrons in the electron transfer chain with the uphill flow of protons across the membrane and a protein that couples the downhill flow of protons to the phosphorylation of ADP

How is the electrochemical proton gradient across the inner mitochondrial membrane created

it is created by one of three means

1. actively transporting protons across the membrane with proton pumps in complex 1,3, and 4

2. chemically removing protons from the matrix through the reduction of ubiquinone and oxygen

3. releasing protons into the inter membrane space through the oxidation of QH2

what does ATP synthase consist of

it consists of and ATPase “knob” (F1 unit) and a membrane-bound, proton transporting base (F0 unit)

what are the units of ATP synthase connected by

they are connected by a shaft and are held in place by a stator

what is the F0 unit

it is a rotor that turns as protons flow through it. its spinning changes the conformation of the F1 unit so that is phosphorylates ADP to form ATP

what does ATP synthase do if the proton gradient dissipates

the spin will be reversed and ATP is hydrolyzed to pump protons from the matrix to the inter membrane space to build a proton gradient

what is produced at the substate level of phosphorylation

4 ATP is produced at this level

what is produced during oxidative phosphorylation

10 NADH and 2 FADH2

how much H+ is required for 1 ATP

4 H+ are required to make one

how much ATP can one NADH and one FADH2 make

2.5 and 1.5 respectively

how much ATP is produced for one molecule of glucose muscles

30

what is the inner mitochondrial membrane impermeable to

it is impermeable to NADH

what does glycolysis generate

it generates NADH which needs to be moved to the mitochondrial matrix to be used

how can electrons from NADH be moved across the membrane (malate aspartate shuttle)

it can be moved by incorporating them into malate which is then transported through malate-a-ketoglutarate integral membrane transporters and can be recovered using the same enzyme

what happens during the glycerol 3 phosphate shuttle

the electrons from the NADH produced during glycolysis will enter the ETC directly and are transferred through glycerol 3-phosphate to reduce FAD to FADH2 in the mitochondrial glycerol 3-phosphate dehydrogenase. the electrons will then be transferred to ubiquinone within the lipid bilayer to form the reduced QH2 and will directly enter the ETC are complex 3

what is oxidative phosphorylation regulated by

it is regulated by substrate availability (NADH and ADP/Pi)

what does inhibitor of F1 do

it prevent hydrolysis of ATP during low oxygen and is only active at lower pH and is encountered when the electron transport is stalled

what does inhibition of oxidative phosphorylation lead to

it leads to accumulation of NADH in the cytosol which causes feedback inhibition cascade up to PFK-1 in glycolysis

how does the ETC generate ATP

it creates a proton-motive force

how is ATP hydrolysis used to power other cellular reactions

it is coupled with energetic reactions

how many ATP are produced out of the oxidation of one molecule of glucose in cardiac cells

32