What is the definition of cellular respiration

The Cellular respiration or internal breathing describes the metabolic processes that the Energy generation serve the cells.

Cells need energy to survive. This energy has to be in the form of so-called ATP (Adenosine triphosphate) are present. This is, so to speak, the body's universal "energy currency". ATP can be produced in the cytoplasm of the cell with the help of grape sugar (glucose). The yield of ATP is very low, however, since the glucose is only incompletely broken down into lactic acid (lactate) during this process. This reaction is called anaerobic glycolysis, d. H. it can take place completely without oxygen.

Higher organisms, so-called eukaryotes (animals, plants and fungi) can also completely break down the glucose. For this purpose, eukaryotic cells have special cell organelles: The mitochondria. So that these completely break down the sugar into carbon dioxide (CO2) and thereby use approx. 15 times more ATP per glucose, they also need oxygen (O2). This is why one speaks here of aerobic glycolysis. So the reason people need to breathe is because the aerobic glycolysis must be maintained in order to provide enough energy to survive.

Exact process:
In the mitochondria, the starting products of glucose are broken down into CO2 in the so-called citrate cycle. This process is called oxidation. In the process, high-energy bonds in the sugar molecule are opened and the energy is released in the form of electrons. However, these electrons are not simply released, but are taken up in a kind of temporary store, (among other things) the so-called NADH.

The NADH now transports the electrons to the respiratory chain, which is located on the mitochondrial wall. Here the electrons and protons are transferred to said oxygen, which reacts to form water (biological oxyhydrogen reaction). During this reaction, a lot of energy is released again, with the help of which ATP can be regenerated in large quantities.

So again: Glucose is broken down into CO2 in the citrate cycle and in the process indirectly transfers electrons to the respiratory chain. There, oxygen is metabolized into water (H2O) and finally ATP is formed.
It is interesting that the inhaled oxygen does not become exhaled carbon dioxide. The former becomes water, while the latter is made from glucose. In other words, what you eat as part of your diet every day.

Cell respiration is divided into three sub-steps (Fig. 2):
  • the Glycolysis
  • the Citric acid cycle
  • and the end oxidation in the Respiratory chain