Electron Transport Chain

Question 1

coupling

Answer 1

ensures rate of fuel oxidation (burning) matches rate of ATP utilised

rate of fuel oxidation/ oxygen consumption or carbon dioxide production = tells us estimate of rate of energy expenditure

Question 2

uncoupling

Answer 2

H+ flows right back in the matrix, no flow through ATP synthase
–> no proton gradient (dissipated)

Question 3

effect of uncoupling

Answer 3

no proton gradient (no control which means protons keep getting pumped with no restriction)
–> NADH rapidly oxidised into NAD+
fuel oxidation continues and oxygen consumption increases
–> but no ATP synthesis, cells die of low ATP levels

Question 4

DNP

Answer 4

dinitrophenol
–> uncoupling agent /chemical compound
- hydrophobic : allows protons to freely cross inner mitochronidral membrane (IMM)
- weak acid = easily undergo protonation and deprotonation ( gain/ lose H+) == carries protons across IMM = no proton gradient

Increases energy expenditure = weight loss

Question 5

UCP-1

Answer 5

uncoupler protein 1 = natural uncoupler
- found in brown adipose tissue specialises for thermogenesis
- UCP-1 is a thermogenin
- abundant in mitochondria

–> found in IMM and when activated, creates channels in IMM for H+ to flow back

Question 6

thermogenesis

Answer 6

function : generate heat

Under hormonal control
* Noradrenalin binds β3-receptors on the surface of brown fat cells –> activation of thermogenin (UCP-1) within mitochondria–> stimulates fatty acid release [fuel source for thermogenesis] –> opens proton channel

• targeted and controllable (healthy unlike DNP)

High in neonates (newborns) : more thermogenesis to generate heat and maintain body temp
–> as we age, decrease in brown adipose tissue (thermogenin)

Question 7

e - Transport and H + pumping
in the ETC

Answer 7

4 complexes in IMM
1) complex I = NADH donates H+/e-
2) complex II = FADH2 donates H+/e-
3) UQ/Q/ubiquinone = accepts H+/e- from complex I and II —> UQ is reuced to UHQ2 and transfers it to complex III
3) complex III = receives H+/e- from UA and transfers to cytochrome c
4) Cyt C = transfers H+/e- to complex IV
5) complex IV = O2–> H2O = oxygen consumption

10 H+ pumped out per NADH, 6 H+ pumped per FADH2
–> complex I pumps 4H+
–> complex III pumps 4H+
–> complex IV pumps 2H+

Question 8

cytochrome C and iron

Answer 8

Cyt C has an iron atom
–> helps transfer of e- from Complex III to Complex IV
–> iron can change oxidation states (ferrous = ferric) when gaining / losing e-

Question 9

how does the exchange electrons between different types of carriers lead to proton pumping

Answer 9

hydrogen carriers (NADH + FADH2) bumps into electron carriers
–> donates H2
–> electron carriers only want e- so H+ is pumped and released into cytoplasm (cytoplasmic side)

Question 10

how to deal with cystolic NADH generation

Answer 10

the NADH generated in glycolysis is in cytoplasm and needs to enter the mitochondria
1) Glycerol 3-Phosphate Shuttle
2) Malate Aspartate Shuttle

Question 11

Malate Aspartate Shuttle

Answer 11

1) oxaloacetate uses H+ (NADH –> NAD+) to form malate
2) malate has own transporter into mitochondrial matrix
3) once in mitochondria, malate –> oxaloacetate (NAD+ –> NADH + e-)

–> more efficiet way of getting NAD out of cytoplasmm into mitochondria
–> full proton pumping potential still maintained

Question 12

Glycerol 3-Phosphate Shuttle

Answer 12

1) NADH + H+ –> NAD+ : allows DHAP (dihydroxyacetone phosphate) to pick up the 2 H+ and convert into G3P
2) G3P gets to the inner mitochondrial membrane
3) G3P back to DHAP by losing hydrogens (G3P dehydrogenase) = FAD to FADH2
–> bypassing complex I

Question 13

4 routes to Q

Answer 13

1) complex I = NADH passed e- to Q
2) complex II = FADH2 passed e- to Q
3) beta oxidation = FADH2 introduced double bond into fatty acyl CoA –> sent e- to Q as well
4) G3P shuttles = from FADH2

Question 14

proton motive force (PMF)

Answer 14

is the combination of both the electrical and concentration components.

1) Protons are positively charged, so when they’re moved across the membrane, they create an electrical difference across that barrier, like a tiny electric charge.

2) By moving protons, the cell also creates a situation where there are more protons on one side of the membrane compared to the other, creating a concentration difference.

Question 15

free radicals

Answer 15

most common place found is ETC = formation at Q

electrons leak from ETC and react with O2 prematurely before protons are combined to form H2O –> reactive oxygen species
–> requires complex III to be vacant so Q is not too overloaded

dangers = cancer/DNA mutations

Question 16

H+ gradient also used in transport

Answer 16

1) ATP from matrix to be sent out into cytoplasm = (negative charge) = requires H+ to come back to matrix
2) Pi/phosphate = bring in phosphate to combine with ADP –> requires H+ to come in with it into matrix

Question 17

List the components and functions of the ATP synthase and explain the mechanism by which it produces ATP

Answer 17

3 H+ for 1 ATP

1) Protons move back into the mitochondrial matrix –> through the F0 complex of ATP synthase.
[F0 channel has 12 cylindrical proteins]
2) F0 allows flow of protons which causes the γ subunit to turn and drive the rotation of its subunits. [The stator, which anchors the γ subunit]

3) 3H+ causes one rotation of the γ subunit and segments causes conformational changes in the F1 complex located in the mitochondrial matrix.
4) catalytic sites on β subunit activated and causes ADP + Pi = ATP