Horcruxes of Cellular Respiration - Part 3

 

Welcome back, fellow wizards!

You have arrived at the final Horcrux of Cellular Respiration. 

In conclusion to the Bubble Head Charm incantation from Harry Potter, the oxygen molecule obtained through breathing is finally being utilized in the final Horcrux of cellular respiration to produce energy in the form of ATP.

The Final Horcrux: E-LEC-TRON TRANS-PORT CHAIN 

The electron transport chain (ETC) is a series of redox reactions where electrons from the electron carriers, NADH and FADH2, are donated to oxygen molecules. These chain reactions take place in the mitochondrial intermembrane. 

Five complexes of the ETC facilitate the donation of electrons to oxygen for the formation of ATPs and water.

1. Complex I - NADH Dehydrogenase

The 3 NADH electron carriers synthesized in the second Horcrux each donate two electrons to the complex which is transferred to ubiquinone (coenzyme Q, CoQ). 

NADH + CoQ + 5H+ (in the matrix) -------> NAD+  + CoQH2 + 4H+ (to the intermembrane)

2. Complex II - Succinate Dehydrogenase

The FADH2 electron carrier from the second Horcrux donates its electrons to this complex, which causes the oxidation of succinate to fumarate. The process also reduces CoQ as the complex transfers the electron carried by FADH to the ubiquinone. 

Succinate + Q ---------> Fumarate + QH2

3. Complex III - Cytochrome C Reductase

The reduced ubiquinone travels through the mitochondrial membrane to transfer the electrons to complex III. At this complex one electron is donated to two molecules of cytochrome C (Cyt C) as one cytochrome C can accept one electron at a time. Hence, two molecules of cytochrome C are reduced. 

QH2 + 2 Cyt C + 2H+ (in the matrix) ---------> Q +  2 Cyt C+  4H+ (to the intermembrane)

4. Complex IV - Cytochrome C Oxidase 

This complex is responsible for transferring the electrons to oxygen once it is received from the two cytochrome C molecules. Here, the oxygen molecule is split into two atoms of oxygen where each accepting two protons from the matrix. This gives rise to two molecules of water. 

4 Cyt C + O2 + 8H+ (in the matrix) --------> 4 Cyt C + 2 H2O + 4H+ (to the intermembrane)

5. Complex V - ATP Synthase

The protons that were pumped to the intermembrane by Complexes I, III and IV created a proton gradient. ATP synthase, which is a rotating unit, utilizes the energy from the proton gradient to synthesize new molecules of ATP. This process is referred to as chemiosmosis. The formation of ATP in the electron transport chain is termed oxidative phosphorylation. 

ADP + Pi -------> ATP

To visualize the electron transport chain, feel free to watch the video below.

Source: BioMan Biology. (2021). The Electron Transport Chain Explained (Aerobic Respiration) [YouTube Video]. in YouTube. https://www.youtube.com/watch?v=zJNx1DDqIVo

Figure 1: Summary of the biochemical processes in the aerobic cellular respiration

Conclusion of Cellular Respiration

Knowing the three Horcruxes of cellular respiration, I hope you understand how Bubble Head Charm incantation provides the caster with oxygen for aerobic cellular respiration.

Until the following biochemical process!

Do you know:

1. What type of respiration occurs in the absence of oxygen?
2. What is the product of this type of respiration?

References:

Berg, J. M., Tymoczko, J. L., Gatto, G. J., & Lubert Stryer. (2015). Biochemistry (8th ed.). W.H. Freeman & Company, A Macmillan Education Imprint.

Khan Academy. (2016). Oxidative phosphorylation. Khan Academy. https://www.khanacademy.org/science/ap-biology/cellular-energetics/cellular-respiration-ap/a/oxidative-phosphorylation-etc

Nelson, D. L., Lehninger, A. L., & Cox, M. M. (2021). Lehninger Principles of Biochemistry (8th ed.). Basingstoke.