Glucose(C3H4O6) is the most important fuel for the human body. To extract energy from glucose, a whole process must first be completed: dissimilation. Glucose is broken down into carbon dioxide and water, releasing energy: C6H 12O6 + 6O2 → 6CO2 + 6H2O + Σ. This process can be divided into 3 important steps: glycolysis, the citric acid cycle and oxidative phosphorylation. ATP and carbohydrates also play an important role.
Glycolysis
Glycolysis is a 10-step process in which glucose is converted into pyruvic acid. This releases energy for the formation of ATP (C10H16N5O13P3, adenosine triphosphate) (see below), an important energy carrier in the body. High-energy electrons and hydrogen are also bound to NAD+ (C21H28N7O14P2, Nicotinamide Adenine Dinucleotide) according to the following equation: 2NAD+ + 4e- + 2H+ –> 2NADH. Initially, ATP is converted into ADP (adenosine diphosphate) to obtain chemical energy to carry out the reaction. Phosphate attaches to the glucose. Each step shows in blue which enzyme helps with the reaction. After the splitting of Fructose 1,6-disphosphate everything counts double. Ultimately, the pyruvic acid is converted into lactic acid, or goes to the mitochondria to participate in the citric acid cycle .
The citric acid cycle
For the citric acid cycle, a carbon dioxide molecule is first split off from the pyruvic acid. This is called decarboxylation. The remainder is bound to coenzyme A (C21H36N7O16P3S): Acetyl coenzyme A is formed. (A coenzyme is a component that helps an enzyme to fulfill its function) Coenzyme A consists of, among other things, the previously obtained ADP. The acetyl coenzyme A now participates in the citric acid cycle. The formation of NADH from, among others, NAD+, GTP (C10H16N5O14P3, guanosine triphosphate) from, among others, GDP and FADH from, among others, FAD+ (Flavin Adenine Dinucleotide, an electron acceptor just like NAD) creates energy-rich compounds that can be used for everything. NADH and FADH2 can donate their energy through oxidative phosphorylation .
Oxidative phosphorylation
During oxidative phosphorylation, the electrons released by NADG and FADH2 are passed on to other electron acceptors in a chain of reactions. This process is called the electron transport chain. Here the electrons always fall into an orbit closer to the atomic nucleus. The energy released is used to transport ions through the interior of the mitochondrial membrane. The concentration difference that this creates on either side of this membrane is used as an energy source for the synthesis of ATP. In the final step, the electrons, together with hydrogen and oxygen, form water again.
ATP
ATP (C10H16N5O13P3, adenosine triphosphate) is an important energy supply in the body. The phosphate (P3) stores energy that is transported throughout the body in ATP.The energy transported in the phosphate bonds can be used for many purposes, including muscle contraction. On the right you can see the splitting of ATP into ADP and phosphate. ATP can be made from ADP, which also produces AMP (adenosine monophosphate): 2 ADP → ATP + AMP. Energy can also be extracted from ADP according to the reaction: ADP → AMP + Pi. Another way to get energy from ATP is splitting it into AMP and PPi (pyrophosphate): ATP → AMP + PPi. PPi can then be converted into Pi by reacting with water: PPi + H2O → 2 Pi. AMP can be regenerated into ATP by 2 reactions: AMP + ATP → 2 ADP and then 2 ADP + 2 Pi → 2 ATP.ATP can also be formed using the GTP obtained in the citric acid cycle: ADP + GTP ATP + GDP.
Carbohydrates
Carbohydrates serve as an energy source. The main effect of carbohydrates is to maintain blood glucose levels. The carbohydrates are converted into glycogen, a polymer of glucose, with the glucose units on either side linked together. Glycogen is used as an easily accessible energy supply. With a surplus of glucose, glycogen is built up, with a shortage it is broken down. It is important for an athlete to have a sufficient supply of glycogen available. Otherwise he can quickly tire and become injured. (see: Overtraining in sports) During recovery, carbohydrates are also very important: the lost energy must be replenished.