Lecture 26

Question 1

Explain what determines the flow of electrons

Answer 1

Electrons flow from molecules with lower E0 (standard redox potential) to molecules with higher E0

Question 2

The difference in E0 is associated with DeltaG. Describe the relationship between these 2. State the equation that describes this relationship

Answer 2

Delta E0 is inversely related to Delta G

Delta G = -nF Delta E0

Question 3

Who proposed the chemiosmotic hypothesis? State the 3 postulates that the chemiosmotic theory is composed of?

Answer 3

Peter Mitchell

1. The mito ETC translocates protons across the inner mito membrane as electrons flow through the ETC
2. ATP synthase uses the proton motive force (pmf) to drive the phosphorylation of ADP (creating ATP)
3. The inner mito membrane is impermeable to H+ and OH- ions (otherwise the pmf cannot be established bc protons will not have to move back through ATP synthase)

Question 4

What 2 factors constitute the establishment of the pmf that drives the ATP synthesis by complex V?

Answer 4

1. pH gradient (Delta ph)

2. Membrane potential (Delta )

Question 5

Describe the structure of ATP synthase and its location in the cell. (include subunits)

Answer 5

“Ball and stick” structure

F0 subunit: “stick part” is embedded in the membrane and has a proton channel

F1 subunit: “ball part” protrudes into the matrix and contains catalytic domains

Question 6

State the 5 subunits of the F1 subunit of ATP synthase. Describe their arrangement

Answer 6

Alpha3
Beta3
Gamma
Delta 
Epsilon

Alpha3 and Beta3 are arranged in a hexameric ring and Beta3 is the only catalytically active one

Above Alpha3 and Beta3 is a “stalk” composed of Gamma and Epsilon proteins

The Gamma subunit has a long helical coil that extends into the center of the Alpha3 and Beta3 hexamer

Question 7

True or False:

Alpha3 and Beta3 both bind to nucleotides and both are catalytically active. explain.

Answer 7

False

Alpha3 and Beta3 both bind to nucleotides HOWEVER Beta3 is the only catalytically active one

Question 8

Explain the structures that maintain the curvature of the mito cristae and why this curvature is favorable.

Answer 8

ATP synthase molecules form dimers with one another and those dimers then form oligomers

These oligomers stabilize the curvature of the mito cristae by stabilizing rotational forces required for catalysis

This curvature allows the proton gradient to be formed in close proximity to ATP synthate

Question 9

Synthesizing 1 mol of ATP requires passage of what across the membrane? explain why this answer is so specific.

Answer 9

1 mol ATP requires 3+1 H+ passage

3 protons enter the F0 subunit and spins it (like a turbine) and then exits the matrix

The last proton is used to drive the ADP + Pi to ATP reaction

Question 10

What is oligomycin? what is it’s mechanism?

Answer 10

Oligomycin: an antibiotic that is a potent inhibitor of ATP synthase (complex V) by inhibiting proton transport through it’s channel

Question 11

Describe the mechanism of action of ATP-ADP translocase. Which mito membrane are these found in?

Answer 11

ATP and ADP are not permeable across the mito membrane, so ATP-ADP translocase serves as their carrier

Flow of ATP and ADP are coupled in such a way that ADP enters the matrix ONLY if ATP leaves

ATP-ADP translocase is found in BOTH mito membranes

Question 12

Since NADH/FADH2 cannot cross the mito membrane, what 2 systems help it enter the mito? Where in the body are these systems found

Answer 12

1. Malate-aspartate shuttle system: operates in the heart, liver, and kidneys
2. Glycerophosphate shuttle system: operates in skeletal muscle and the brain

Question 13

Between the Malate Aspartate and Glycerophosphate shuttles, does it move NADH or FADH2? Include which specific ETC protein moves the NADH/FADH2 and where in the mito this molecule is moved into.

Answer 13

Malate Aspartate Shuttle:
Moves NADH to enter the ETC at Complex I
NADH gets moved into the mito matrix

Glycerophosphate Shuttle: Moves FADH2 to join the ETC at CoQ
FADH2 gets moved into the Inner mito membrane

Question 14

Respiratory control refers to what? give the other name for respiratory control

Answer 14

Respiratory control (aka Acceptor Control): regulation of cellular respiration by ADP levels (or ATP)

Electrons only flow when ADP is phosphorylated into ATP

Question 15

State the 3 outcomes associated with the inhibition of the transfer of electrons during OxPhos reactions

Answer 15

1. decrease in the pumping of protons
2. decrease in the proton gradient
3. inhibition in the synthesis of ATP

Question 16

Briefly explain the process by which heat generation is conducted in brown adipose tissue

Answer 16

uncoupling OxPhos from ATP synthesis and using the OxPhos in generating heat (hibernating animals do this)

Question 17

Which inner mito membrane uncoupling protein is used to conduct OxPhos in order to generate heat? Explain it’s function.

Answer 17

Thermogenin (aka UCP 1): transfers protons from cytoplasm to the matrix side of the mito to generate heat instead of ATP

Question 18

What does UCP 2 and UCP 3 do?

Answer 18

these also uncouple OxPhos from ATP synthesis (not specific about them in the lecture)

these play a role in energy homeostasis

Question 19

What is the other name for Thermogenin?

Answer 19

Thermogenin (aka UCP 1): transfers protons from cytoplasm to the matrix side of the mito to generate heat instead of ATP