Q1. To confirm Boyer’s “binding change model” for the ATP synthase, the F1 subun

Question

Q1.

To confirm Boyer’s “binding change model” for the ATP synthase, the F1 subunit was removed from the inner mitochondrial membrane and attached upside down to a glass slide (such that the ? and ? subunits were directly attached to the glass slide, and the ?-rotor was pointing straight up). A fluorescently-labeled actin filament was then attached to the ?-rotor to allow observation of its rotation in the microscope, as shown below. Prior to adding ATP, no movement was observed.

Part 1. Upon adding ATP, what result to do you expect?

Select ONE option:

1. No movement at all

2. Back and forth movement across 180 degrees

3. Rotation in 120 degree intervals

4. Rotation in 90 degree intervals

Part 2. Do you expect that the movement of the actin filament depends on the synthesis or the hydrolysis of ATP in this experiment?

Select ONE option:

1. hydrolysis of ATP

2. synthesis of ATP

3. cannot tell

Part 3. What do you expect to observe after a full cycle of the labelled actin filament, assuming each active site goes through the three binding states?

Select ONE option:

1. synthesis of one molecule of ATP

2. hydrolysis of one molecule of ATP

3. synthesis of three molecules of ATP

4. hydrolysis of three molecules of ATP

Q2.

The following questions ask you to consider what would happen if isolated mitochondria provided with both NADH and oxygen (O2) were treated with agents that prevent the reduction of various components of the ETC. Recall that redox reactions occur sequentially in the electron transport chain. If a certain redox reaction is blocked, all the reactions following it will be blocked as well (much like a traffic jam on a road).

Note that NADH is the only available fuel for the mitochondria in this scenario.

Part 1. Rotenone is a small molecule that prevents NADH from reducing complex I. Which molecule(s) could be reduced if the isolated mitochondria were treated with rotenone?

(Select ALL that apply.)

A. Complex I

B. Complex III

C. Complex IV

D. Coenzyme Q

E. Cytochrome c

F. Oxygen

G. None of the above

Part 2. Antimycin A is a small molecule that inhibits reduction of cytochrome c. Which molecule(s) could be reduced if a cell were treated with antimycin A?

(Select ALL that apply.)

A. Complex I

B. Complex III

C. Complex IV

D. Coenzyme Q

E. Cytochrome c

F. Oxygen

G. None of the above

Part 3. Cyanide (CN-) prevents the reduction of oxygen. Which molecule(s) could be reduced if a cell were treated with cyanide?

(Select ALL that apply.)

A. Complex I

B. Complex III

C. Complex IV

D. Coenzyme Q

E. Cytochrome c

F. Oxygen

G. None of the above

Q3.

Experiment 1. Two sets of cells are subjected to a FRAP experiment. One cell has a lipid bilayer that includes cholesterol, which makes it less fluid; and the other cell has a membrane made purely of phospholipids. The results are shown below. Which curve, A or B, was obtained from cells with a membrane that includes cholesterol?

Select ONE option:

1. A

2. B

Experiment 2. Membrane fluidity decreases as the temperature cools. If you conducted two FRAP experiments with the same cell, one experiment at warm temperature, and the other at a cooler temperature, which of the FRAP curves below best represents the cell at the warmer temperature?

Select ONE option:

1. A

2. B

Q4.

Part 1. The movement of high-energy electrons to gradually lower energy levels requires _______ to serve as the final electron acceptor.

Select ONE option:

A. Oxygen

B. Carbon dioxide

C. Water

D. ATP

Part 2. The movement of high-energy electrons to gradually lower energy levels releases the energy from food such that it can be coupled to making ________.

Select ONE option:

A. Oxygen

B. Carbon dioxide

C. Water

D. ATP

Part 3. A molecule that releases electrons is called an __________.

Select ONE option:

A. Electron donor

B. Electron acceptor

Part 4. A molecule that receives electrons is _________.

Select ONE option:

A. oxidised

B. reduced

Part 5. A molecule that receives electrons is called an _________.

Select ONE option:

A. Electron donor

B. Electron acceptor

Part 6. A molecule that gives up electrons is ___________.

Select ONE option:

A. oxidised

B. reduced

Actin filam Streptavidin ?3?3? complex His-tag Coverslip coated with Ni-NTA

Explanation / Answer

Q1: Part 1: rotation occurs in intervals of 1200. Hence option 3 is correct.

Part 2: Since F1 subunit has ATPase activity hence it will hydrolyse ATPs in the absence of its Fo subunit. Hence option 1 is correct.

Q2: Part 1: option G is correct. Rotenone inhibits electron transfer from complex 1 itself, hence blockage of electron transfer at complex 1 will lead to shutting down of the whole electron transfer chain and none of the above molecules can be reduced.  

Part 2: A & D are correct. Antimycin A inhibits electron transfer from cyt b to cytc1, shutting down further electron transfer. Hence Coenzyme Q and complex 1 will be reduced.

Part 3: A,B,C,D,E. cyanide inhibits terminal electron transfer from cyt(a+a3) to molecular oxygen, hence all the components of ETc will be reduced except oxygen.

Q3: Experiment 1: 2. is correct Since cholesterol makes the membrane less fluid hence the membrane will not reseal faster as compared to membrane made up of phospholipids, Plot B represents less rapid movement of phospholipids as compared to plot A , hence plot B represents cell with membrane that includes cholesterol.

Experiment 2: 1. is correct. Higher temperature leads to more membrane fluidity due to increased motion of phospholipids, hence at higher temperature they will reseal the photobleached area much faster as compared to lower temperatures. In plot A there is a rapid increase in fluorescence after photobleaching due to rapid movement of phospholipids as a result of increased temperature.

Q4: Part 1: Oxygen is the terminal electron acceptor in movement of higher energy electrons to lower energy electrons.

Part 2: The energy released during movement of electrons from high energy to lower energy states is coupled with formation of ATP from ADP and Pi.

Part 3: A molecule that releases electron is known as electron donor.

Part 4: A molecule which receives electrons is said to be reduced.

Part 5: A molecule taht receives electrons is called an electron acceptor.

Part 6: A molecule taht gives up e;ectrons is known as electron donor.

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