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.

Horcruxes of Cellular Respiration - Part 2

Welcome back, fellow wizards!

Today, we will be exploring the second Horcrux of cellular respiration.

Do you remember the Bubble Head Charm incantation from Harry Potter that provides a steady supply of oxygen for respiration? Well, the presence of oxygen stimulates cells in the body to respire aerobically. In aerobic respiration, the Cycle of Krebs comes directly after glycolysis. 

The Second Horcrux: CY-CLE OF KRE-BS

The second Horcrux of cellular respiration can also be referred to as the Tricarboxylic Acid (TCA) Cycle or the Citric Acid Cycle. 

The pyruvate molecules synthesized by the first Horcrux of cellular respiration underwent decarboxylation and oxidation to produce the acetyl coenzyme A (acetyl CoA) required for the cycle of Krebs. This process serves as an irreversible link between glycolysis and the cycle of Krebs.

Pyruvate + CoA + NAD+ ---------> Acetyl CoA + NADH + CO2 + H+

The enzyme that catalyzes this conversion is the pyruvate dehydrogenase complex. 

The acetyl CoA, which is a 2-carbon molecule, enters the citric acid cycle and condenses with a 4-carbon molecule to give rise to a 6-carbon molecule. The 4-carbon molecule is oxaloacetate while the 6-carbon molecule is citrate.

Acetyl CoA (2C) + Oxaloacetate (4C) -------> Citrate (6C)

This reaction is catalyzed by the enzyme citrate synthetase. 

Citrate is then converted to other intermediates via a group of enzymes as seen in the figure below.

Figure 1: Diagram outlining the different metabolic intermediates and enzymes of the citric acid cycle.

Some important factors to know about the Cycle of Krebs.

1. This cycle uses acetyl CoA to extract the maximum number of electrons from it as it is carbon fuel. These extracted electrons are sent to the electron transport chain, the third and final Horcrux of cellular respiration. The electron carriers are NADH and flavin adenine dinucleotide (FADH).  
2. ATP is generated from the GTP synthesized upon the conversion of Succinyl CoA to Succinate. This is another example of substrate-level phosphorylation. The generation of ATP is due to the large energy reserve in the thioester of the succinyl CoA

Note: 1 FADH2, 3 NADH and 1 ATP were generated in one cycle of the citric acid cycle from one molecule of acetyl CoA.

For more on the second Horcrux of cellular respiration, feel free to watch the video below.

Source: MEDSimplified. (2020). Krebs Cylcle Trick How to remember krebs cycle FOREVER!! [YouTube Video]. In YouTube. https://www.youtube.com/watch?v=RnL71vnCMCY

Until the third and final Horcrux - Electron Transport Chain!

Do you know:

1. The name of the enzyme in the Krebs Cycle that catalyzes Fumerate into Malate?
2. Where in the cell the Krebs Cycle takes place?

Feel free to share your response.

References:

Abali, E. E., Cline, S. D., Franklin, D. S., & Viselli, S. M. (2021). Lippincott Illustrated Reviews: Biochemistry. Wolters Kluwer Health.

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

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

Horcruxes of Cellular Respiration - Part 1

 

Have you ever heard of the Bubble Head Charm incantation from the Harry Potter movies? It is an incredible spell that permits one to breathe in areas they cannot, for example, the ocean. A bubble forms around the caster's head, providing them with a continuous oxygen supply. Breathing underwater is an incredible feat, however, it only allows for gaseous exchange via inhalation and exhalation. 

"What is the connection between the Bubble Head Charm and cellular respiration?" you may ask.

Well, the link is oxygen gas. Aren't you curious to know what the body does to the oxygen for you to respire?

Cellular Respiration

If I ask you, 'what is cellular respiration?', terms such as glucose, oxygen and energy would be a part of your response. You may even state the formula equation to validate your point. Figure 1 below demonstrates a simplified version of how the molecular oxygen inhaled is utilized in the mitochondria of the cells alongside glucose obtained from food to produce energy. 

Figure 1: Schematic diagram outlining the cellular respiration process in the human body.

Cellular respiration is a set of metabolic reactions that converts biomolecules into energy-storing molecules, adenosine triphosphate (ATP). To arrive at ATP, glucose must first enter the cells and be converted into a usable form in the first set of reactions, glycolysis.

The First Horcrux: GLY-COL-Y-SIS

This cycle converts glucose into a 3-carbon compound termed pyruvate via a ten-step series of catalytic reactions. The ten steps are further classified into the preparatory and the payoff phases. These events take place in the cytoplasm of cells. 

Preparatory Phase:

The preparatory phase aims to convert glucose into two 3-carbon molecules via the first four steps. Two ATPs are used for phosphorylation. 

When glucose enters the cell through transmembrane proteins, it is immediately phosphorylated by the enzyme hexokinase in the presence of an ATP. Hexokinase adds a phosphate group to six-carbon sugars. Therefore, glucose is converted into a molecule called glucose-6-phosphate. 

Glucose-6-phosphate is further catalyzed by enzymes until two 3-carbon molecules, glyceraldehyde-3-phosphate and dihydroxyacetone phosphate. The latter molecule is converted to its isomer by the enzyme triose phosphate isomerase. Thus, at the end of the preparation phase, there are two glyceraldehyde-3-phosphate. 

Figure 2: Summary of the preparatory phase of glycolysis. 

[Adapted from Biochemistry by Berg et al. (2015)]

Payoff Phase:

The second stage ends with the production of two pyruvate molecules from two molecules of 1,3-bisphosphoglycerate. 

Glyceraldehyde-3-phosphate first undergoes oxidative conversion to 1,3-bisphosphoglycerate. Two molecules of the coenzyme, nicotinamide adenine dinucleotide and hydrogen (NADH), are utilised to facilitate the conversion. 

From that point onward, four ATPs are synthesized. The synthesis of adenine triphosphates (ATP) via glycolysis is referred to as Substrate-level phosphorylation. This is one way ATP can be generated in cells. 

Figure 3: Summary of the preparatory phase of glycolysis. 

[Adapted from Biochemistry by Berg et al. (2015)]

At the end of the glycolytic process, there is a net production of two ATP molecules. 

Why?

Answer: In the preparation phase, 2 ATPs were used, while in the payoff phase, 4 ATPs were synthesized. Therefore, 4 ATPs - 2 ATPs = 2 ATPs.

Until the next Horcrux - Cycle of Krebs!

Do you know:

1. Where is glucose phosphorylated in the body?
2. Why is glucose phosphorylated upon entry into the cells?

Feel free to share your responses. 

References:

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

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

Tarantino, C. (2020). Cellular Respiration - What Is It, Its Purpose, and More (A. Haag, E. Miao, & A. Hernández, Eds.). Osmosis. https://www.osmosis.org/answers/cellular-respiration

Tymoczko, J. L., Berg, J. M., J, G., & Lubert Stryer. (2019). Biochemistry : a short course (4th ed.). W.H. Freeman And Company.

Welcome to Wizardry!

Biochemistry is one of the fundamental aspects of learning about various chemical processes in all living organisms. 

To understand it, one must dive into the cauldron known as the body and analyse the different ingredients, which include cells, tissues and organs. The body is a remarkable structure filled with magical components that are misunderstood and underappreciated.

Source: Gregorio, F. (2013, December 30). Introduction to Biochemistry HD. Www.youtube.com; YouTube. https://www.youtube.com/watch?v=tpBAmzQ_pUE

Wizards of Biochemistry explores the wonders of various biochemical processes in the human body. It aims to spread an appreciation of these processes that each cell performs to make humans a functioning whole. 

Come with me on this journey as we cast spells and observe different processes come to life. 

Before we begin, tell me:

1. What are some biochemical processes in the body that you know about? 
2. Which do you enjoy learning about the most?