All living things derive the energy needed for their activities by a process called cellular respiration, which takes place in each of their cells.
Cellular respiration is formed by a series of reactions that occur inside the cell and that allow you to extract energy from food. In animals, food, through digestion, is reduced to simple substances: the polysaccharides are reduced to glucose, amino acids, proteins, triglycerides to glycerol and fatty acids. All of these simple substances in the blood and then come through it can reach all the cells. In plants, however, through photosynthesis, glucose is produced directly from cells of the green parts, then pour it into the lymph processed through it reaches all parts of the plant itself.
Elementary substances within cells are "burned", that is combined with oxygen coming to the air breathing animals, for plants from the openings of the leaves, roots and trunk. The combustion takes place through a very large number of chemical reactions, each catalyzed by a specific enzyme that allows cells to get energy without reaching the high temperatures reached by burning "flame" the same substances. In fact, the cells could not tolerate such high temperatures. In addition, cell respiration food energy is converted into heat, as happens in the combustion flame, but in ATP, the energy currency used by cells to all their activities.
cellularePer breathing easy now only tackle the energy metabolism of glucose, the set of chemical reactions by which glucose produces energy, making only some reference to energy metabolism of other simple substances (amino acids, glycerol and fatty acids).
The first part of the combustion of glucose occurs in the cytoplasm, is known as glycolysis and occurs in virtually all cells, from the simplest prokaryotes to the eukaryotic cells of our body. Glycolysis, is formed by a series of reactions during which, from the skeleton of glucose, are taken from hydrogen atoms, which are temporarily given to a compound called NADH. During this phase are also generated two molecules of ATP for every molecule entering the cycle, while the oxygen is not used. In addition to glucose, and the polysaccharides that are formed from it (glycogen and starch), other monosaccharides and some disaccharides can be used in glycolysis.
What remains to be demolished glucose enters the second stage of combustion, called the Krebs cycle, which takes place within the mitochondrial matrix or the solution that is contained within the inner membrane of mitochondria and folded. In this cycle can also participate in amino acids and fatty acids, that reach it by ways other than glycolysis, taking place in the cytoplasm and at which are also suitably treated and processed. During the Krebs cycle is finished to remove hydrogen atoms from the molecule of glucose, to give them to other molecules of NADH and FADH 2 molecules to some, another compound that temporarily holds the hydrogen atoms. At the end of the cycle, which does not require oxygen and is produced during which even some other molecule of ATP, all that remains of the original glucose molecule are six molecules of CO2.
The third and final phase of cellular respiration occurs in mitochondria, more specifically by the dual status of the inner membrane phospholipid, and is called oxidative phosphorylation. During this phase we are carrying out a series of reaction, by means of which all the hydrogen, which in previous stages had been transferred from the glucose molecules of NADH and FADH 2, this now changes from oxygen, which finally comes into play . The combination of hydrogen and oxygen form six molecules of H 2 O for each molecule of glucose is the initial and produce many molecules of ATP.
In the end the whole process of cellular respiration can be summarized in the following reaction:
C6H12O6 + 6 O2 → 6 CO2 + 6 H2O
When it is 38 ATP molecules are produced, which translated into energy terms, corresponding to approximately 40% of the calories that would be obtained by burning a glucose molecule in the air. The energy efficiency of cellular respiration is therefore 40%, about twice that of the more efficient machines invented by man.
In summary we can say that cellular respiration occurs in three phases:
Occurs in the cytoplasm
No need for oxygen
Few molecules of ATP are produced
Escape glucose hydrogen atoms to donate to NADH
Occurs in the mitochondrial matrix
No need for oxygen
Few molecules of ATP are produced
It ends to remove hydrogen from glucose to NADH and FADH 2 to give it away, until all that remains of glucose carbon dioxide.
Occurs in the double state of inner mitochondrial membrane
And 'necessary oxygen
We produce many molecules of ATP
The hydrogen of NADH and FADH 2 is combined with oxygen, producing water.
The 'NAD +, the starting compound that binds a hydrogen atom to form NADH, called nicotinamide dinucleotide adeinin and, as the name suggests, consists of two nucleotides containing adenine.
The FAD, the starting compound to which they bind two atoms of hydrogen to form FADH 2, flavin adenine dinucleotide is called and has a structure similar to that dell'NAD +.