Earrings - DNA

Cellular respiration (overall yield)

This is a subject that usually generates some confusion when I talk about it in my classes. The reason is very simple... many of my students have learned that when a NADH molecule transfers the electrons to the mitochondrial respiratory chain, it is formed 3 ATP, and when it is the FADH2 the donor of the electrons it is produced 2 ATP. When I say in my classes that are in fact 2.5 ATP produced when the electron donor is NADH, and 1.5 when it is the FADH2, there are many students who make a puzzled face. By the way, let me just make a correction to something that I hear very often. It is not correct to say that NADH is converted in 2.5 ATP, instead it should be said that NADH leads to the production of 2.5 ATP, since NADH is not spent on the process and it only gives two electrons. But back to the energy efficiency... another thing that often causes confusion when I talk about the production of 2.5 ATP, is the fact that you are talking about "one half of an ATP". But how do we produce "half ATP"? And what does the chemical point of view of "half ATP"? In reality it is a strange and confusing idea but the justification is very simple. As it is logical, no one produces “half ATP”, what is happening is that the energy released during the transport of electrons along the mitochondrial respiratory chain is sufficient to produce in average ATP 2.5 or 1.5 (depending if the donor of the electrons is NADH or FADH2, respectively). As the process is continuous, the sum of the energy released per a second electron donor is sufficient to ensure one ATP together.

But back to the total amount of ATP, how it gets to the value of 2.5 or 1.5 ATP, and why the 3 and 2 ATP that many learn is wrong? To recap the operation of the mitochondrial respiratory chain, when NADH is the electron donor, it gives two electrons to the complex I, and 4 protons are pumped into the intermembrane space. The electrons pass to the complex II, which pumps more 4 protons into the intermembrane space. Afterwords, the electrons cross the complex IV until they reach the O2, leading to the pumping of 2 more protons into the intermembrane space, which makes a total of 10 protons pumped into the intermembrane space per NADH that transfers the electrons to the respiratory chain. If the electron donor is the FADH2, these are delivered to complex II, which does not pump protons. Then go to complex III, which pumps 4 protons into the intermembrane space, and finally to the compound IV, which pumps more 2 protons, that means, in total are pumped 6 protons. According to the chemiosmotic theory, the protons will return to the matrix in favor of the concentration gradient, releasing energy. It has been shown experimentally that for every 4 protons returning the matrix, it is released sufficient energy to produce an ATP molecule. Thus, when the electron donor is NADH, it is produced 10/4 = 2.5 ATP molecules, and when it is FADH2 it is produced 6/4 = 1.5 ATP!

Scientific achievements in science in 2014

Thank you for the input Vasco! :)
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Video about oxiddation of fatty acids

Tattoo - Evolution (2)

Metabolic map about the role of chaperones in the folding of hemoglobin

(Bio)chemical composition of our body

Thank you for the suggestion Vasco! :)
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Cellular respiration - Chemiosmotic theory

The chemiosmotic theory, postulated in 1961 by Peter Mitchel explains how the transport of electrons along the mitochondrial respiratory chain is related to the synthesis of ATP. In fact, as the electrons go through the respiratory chain complexes, they behave like that are moving down an "energy staircase", always passing gradually to a lower energy level. In other words, there are small amounts of energy that are released, which individually are not useful to the cell. However, part of this energy is used to pump protons into the intermembrane space, that is, part of the energy is stored in the form of an H+ gradient. This gradient allows the accumulation of a large amount of energy, because this is an electrochemical gradient. It is a chemical gradient, because we are talking about an asymmetry of H+ concentrations between the two sides of the inner membrane. But it is also an electrical gradient, as it is also created an asymmetry of charged between both sides of the membrane, because the H+ is pumped into the intermembrane space without sending any counterion. Thus, there is an accumulation of positive charges in the intermembrane space, as compared while the matrix becomes more negative. By now many must be wondering "But what is the use of this process? Why does the cell needs a gradient of H+? "The chemiosmotic theory explains just that!

In addition to the mitochondrial respiratory chain complexes, there is also a membrane enzyme (localized in the inner membrane), called mitochondrial ATP synthase (more about this enzyme here). This enzyme has a catalytic subunit, responsible for the synthesis of ATP, and a subunit that functions as a transmembrane pore for the passage of protons. So, the idea is simple... the protons that accumulate in the intermembrane space, will cross the inner membrane through this pore, and since this transport occurs driven by the electrochemical gradient, it releases energy. This energy is used by ATP synthase to produce ATP.