Module 9: Electron Transport Chain & ATP Synthesis

Question 1

ETC components

Answer 1

NADH and FADH2 donate their electrons
5 pr- complexes: I, II, III, IV, V

First 4 pr- complexes: accept electrons and shuttle them along, and pump protons out of the mitochondrial matrix into the inter- membrane space

2 e- carriers: coenzyme Q and cytochrome c
shuttle the electrons b/w pr- complexes
lipid soluble

Question 2

Electron Shuttling & Redox centres (4)

Answer 2

electrons move through redox centres w progressively greater reduction potential (highest=oxygen)
pr- complexes themselves not reversibly reduced/oxidized

Complexes contain combo of 2/more redox centres: coenzymes, Fe-S clusters, cytochromes, copper

Question 3

How Are Electrons Shuttled Through The Electron Transport Chain?

Answer 3

NADH donates its e- to complex I, which passes them to III then IV
FADH2 donate its e- to II, which passes them to III then IV

oenzyme Q shuttles e- through the membrane to complex III
cytochrome c shuttles e- from complex III to complex IV

NADH has the lowest reduction potential (or the least affinity for electrons), whereas oxygen has the highest reduction potential (or the highest affinity for electrons)

Question 4

Complex I: NADH & Ubiquinone

Answer 4

transfer 2 e- from NADH to ubiquinone
4 protons transporter from matrix (N) to inter-membrane space (P) per 1 NADH

reduced coenzyme Q picks up 2 protons -transported by proton wires

Question 5

Complex II: Succinate to Ubiquinone

Answer 5

FAD accepts 2 e- from succinate
e- passed via Fe-S centre to ubiquinone (reduced to QH2)
does not transport protons

Succinate dehydrogenase:

• convert succinate to fumarate in CAC
• capture and donate e- in ETC

Question 6

Complex III: Ubiquinone to Cytochrome C

Answer 6

use 2 e- from QH2 to reduce 2 mol of cytochrome c
contain Fe-S clusters, cytochrome b and c
4 additional protons moved to inter-membrane space

Question 7

Complex IV: Cytochrome C to O2

Answer 7

4 e- used to reduce 1 O2 mol into 2 H2O

4 protons picked up from matrix (N) and passed to inter-membrane space (P)

Question 8

How many protons are pumped for each pair of electrons?

Answer 8

Complex I: 4
Complex II: none
Complex III: 4
Complex IV: 2 (total 4)

Question 9

Creation Of A Chemiosmotic Gradient

Answer 9

high concentration of protons outside of the inner membrane, relative to the inside of the matrix
Electrochemical gradient–>’chemical’ b/c create a lower pH outside of the inner membrane, and ‘electrical’ b/c positive charge of the protons wish to reach equilibrium by entering the mitochondrial matrix where the relative charge is negative
cell harnesses that potential energy and uses it to drive the synthesis of ATP

Question 10

F1-F0 ATP synthase

describe both subunits

Answer 10

composed of multiple subunit
F0 subunit: proton channel, responsible for allowing protons to enter the matrix
-integral membrane complex
-transports H+ from IMS to matrix, dissipating gradient
-energy transferred to F1 to catalyze phosphorylation
F1 subunit: bulbous portion of the complex on the matrix side of the inner membrane, responsible for synthesizing ATP
-soluble complex in matrix
-individually catalyzes hydrolysis of ATP

F0 and F1 subunits are held together by a protein ‘stalk’ which serves to connect the two subunits

Question 11

Mechanism Of ATP Synthesis

Answer 11

high concentration of protons on the outside of the inner membrane and a relatively lower concentration of protons inside the matrix
When protons pass through the F0 channel and stalk from the outside to the inside of the matrix, this drives the ATP synthase in the F1 subunit, which has an ADP and an inorganic phosphate (Pi) present in the active site
proton drives conformational change in active site, therefore driving catalysis of the formation of a new high energy phosphoanhydride bond in ATP

Question 12

P/O ratio

Answer 12

NADH pumps 10 protons, yielding 3 ATP

FADH2 pumps 6 protons, yielding 2 ATP

Question 13

How Many ATP Are Generated From The Breakdown Of Glucose?

Answer 13

Glucose =2 ATP
-2 NADH =6ATP
-2 pyruvate:
2 NADH=6 ATP
2 acetyl CoA:
-6 NADH=18 ATP
-2 FADH2=4 ATP
-2 GTP=2 ATP

TOTAL: 38 ATP

Question 14

Ways to access cytosolic NADH

Answer 14

NADH generated inside the mitochondria through PDH reaction and CAC have easy access to ETC
However, NADH generated from glycolysis (occurs in the cytosol) will not have access to ETC

2 mechanisms:

1. glycerol- 3-phosphate shuttle
2. malate-aspartate shuttle