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.
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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.
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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:
- Where is glucose phosphorylated in the body?
- 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.
Glucose is phosphorylated in the liver and the reason is so that glucose remains in the cell and does not exit.
ReplyDelete1. In the liver.
ReplyDelete2. To prevent it from leaving the cells due to becoming impermeable.
1. In the liver
ReplyDelete2. To trap the glucose molecules inside the cells (which will be beneficial for giving the body energy), to make ATP and to facilitate enzyme bonding and specificity.
Glucose is phosphorylated inside the liver. This occurs upon entry into the cell to prevent glucose from diffusing to the outside of the cell which allows for the continuation of glycolysis that produces energy (ATP), and the reduction of glucose concentration inside the cell to allow more glucose to be taken up from the bloodstream.
ReplyDelete