Oxidative Phosphorylation and MCQs
During the transport of electrons through the ETC, a portion of energy liberated is conserved. The energy is conserved by the energy transducing system by which electrical energy is converted to chemical energy. Since the energy is conserved in the form of ATP through the phosphorylation of ADP to ATP by F0F1ATPase; so the overall process is known as oxidative phosphorylation.
Energy conserving or coupling sites:
There are 3 energy conserving or coupling sites of ETC which are Complex-1, Complex-3 and Complex-4. These 3 provide energy to make ATP from ADP and a phosphate by F0F1ATPase enzyme.
Electrons that enter the ETC through NADH, pass through all the 3 sites and yields 2.5 ATPs. The electrons that enter through FADH2, pass through only 2 sites and thus yields 1.5 ATPs.
Mechanism of oxidative phosphorylation
Chemoisomotic Theory
The chemiosmotic coupling hypothesis was proposed by a British biochemist: Peter Mitchell. This theory explains the mechanism of oxidative phosphorylation.
The theory states that the energy released from oxidation, generates a electrochemical potential by pumping of protons across the inner mitochondrial membrane. The energy in the electrochemical potential can be converted to ATP.
This theory has 3 basic principles:
- The major electron carriers are present in complex-1, 3 and 4, which then cross the inner mitochondrial membrane. This structural feature of ETC allows the proton to be pumped across the inner mitochondrial membrane, while electrons are passed from one carrier to another.
- The inner mitochondrial membrane is impermeable to protons so that their pumping yields electrochemical potential
- Because of this electrochemical potential, the H+ is brought out by ETC and flows back to the mitochondrial matrix through a specific H+ channel.
Substrate level phosphorylation
In addition to oxidative phosphorylation, some ATPs are also produced in some steps of metabolic pathway. For example:
In glycolysis, conversion of glyceraldehydes-3-phosphate to 1,3-bisphosphoglycerate yields energy in forms of ATP by 3-phosphoglycerate kinase enzyme. Thus the formation of ATP without involvement of ETC and molecular O2, it is known as substrate level phosphorylation.
Multiple Choice Questions (MCQs)
1. The energy liberated is conserved by which system?
A. Energy translating system
B. Energy transducing system
C. Energy transparent system
D. None of the above
2. The conserved electrical energy is changed in which form of energy?
A. Mechanical energy
B. Potential energy
C. Chemical energy
D. All of the above
3. The energy is conserved in which form?
A. ATP
B. AMP
C. ADP
D. Both A and b
4. Phosphorylation of which energy molecule yields ATP?
A. NAD
B. ADP
C. AMP
D. UTP
5. Which enzyme catalyzes the phosphorylation?
A. Kinases
B. Oxidoreductase
C. F0F1ATPase
D. All of the above
6. Which of the following complex is known as coupling sites?
A. Complex-1
B. Complex-4
c. Complex-3
D. All of the above
7. Electrons entering through NADH pass through how many coupling sites?
A. 2
B. 3
C. 1
D. 4
8. Match the following-
9. Electrons entering through FADH2 pass through how many coupling sites?
A. 4
B. 3
C. 2
D. 1
10. The chemiosmotic theory is given by which biochemist?
A. James Watson
b. Erwin Chargaff
C. Peter Mitchell
D. Francis Crick
11. according to the chemiosmotic theory, what is generated due to release of energy from oxidation?
A. ATP
B. ADP
C. Electrical energy
D. Electrochemical potential
12. Which of the following statement is NOT true?
13. Which of the following is impermeable to inner mitochondrial membrane?
A. ATP
B. ADP
C. Proton
D. Electron
14. How many ATPs are generated if the electrons enter through NADH?
A. 2
B. 2.5
C. 3.5
D. 1.5
15. How many ATPs are generated if the electrons enter through FADH2?
A. 2
B. 2.5
C. 3.5
D. 1.5
ANSWERS:-
1. Energy transducing system
2. Chemical energy
3. ATP
4. ADP
5. F0F1ATPase
6. All of the above
7. 3
8.
9. 2
10. Peter Mitchell
11. Electrochemical potential
12.
13. Proton
14. 2.5
15. 1.5