Why tca cycle is dependent on oxygen

Respiratory electron transport is a current of electrons that passes through proteins in the inner mitochondrial membrane. This is similar in many ways to the electric current of photosynthetic electron transport in chloroplasts.

Ultimately, they are passed to oxygen O 2. O 2 becomes two molecules of water H 2 O after receiving four electrons. This is how oxygen is used by cell respiration. It is a safe endpoint for the electric current that drives the synthesis of ATP. The electron transport between proteins of the inner mitochondrial membrane makes ATP adenosine tri phosphate from ADP adenosine di phosphate by adding the third phosphate. It does not do this directly, however.

It can be used to drive a tiny turbine. Recall also that solutes move so as to create even distribution and electrical neutrality. It can only do so through the appropriate transport protein, however. The resulting compound is called acetyl CoA. Figure 1. Acetyl CoA can be used in a variety of ways by the cell, but its major function is to deliver the acetyl group derived from pyruvate to the next pathway in glucose catabolism.

Like the conversion of pyruvate to acetyl CoA, the citric acid cycle in eukaryotic cells takes place in the matrix of the mitochondria. Unlike glycolysis, the citric acid cycle is a closed loop: The last part of the pathway regenerates the compound used in the first step. The eight steps of the cycle are a series of chemical reactions that produces the following from each molecule of pyruvate remember that there are 2 molecules of pyruvate produced per molecule of glucose that originally went into glycolysis :.

Part of this is considered an aerobic pathway oxygen-requiring because the NADH and FADH 2 produced must transfer their electrons to the next pathway in the system, which will use oxygen.

This molecule of acetyl CoA is then further converted to be used in the next pathway of metabolism, the citric acid cycle. The citric acid cycle is a key component of the metabolic pathway by which all aerobic organisms generate energy. The citric acid cycle, shown in —also known as the tricarboxylic acid cycle TCA cycle or the Krebs cycle—is a series of chemical reactions used by all aerobic organisms to generate energy through the oxidation of acetate—derived from carbohydrates, fats, and proteins—into carbon dioxide.

The cycle provides precursors including certain amino acids as well as the reducing agent NADH that is used in numerous biochemical reactions.

Its central importance to many biochemical pathways suggests that it was one of the earliest established components of cellular metabolism; it may have originated abiogenically. The Citric Acid Cycle : The citric acid cycle, or Krebs cycle, is a series of chemical reactions used by all aerobic organisms to generate energy through the oxidization of acetate—derived from carbohydrates, fats, and proteins—into carbon dioxide. In addition, the cycle provides precursors including certain amino acids as well as the reducing agent NADH that is used in numerous biochemical reactions.

The name of this metabolic pathway is derived from citric acid, a type of tricarboxylic acid that is first consumed and then regenerated by this sequence of reactions to complete the cycle. The net result of these two closely linked pathways is the oxidation of nutrients to produce usable energy in the form of ATP. Components of the TCA cycle were derived from anaerobic bacteria, and the TCA cycle itself may have evolved more than once.

Theoretically there are several alternatives to the TCA cycle, however the TCA cycle appears to be the most efficient. If several alternatives independently evolved, they all rapidly converged to the TCA cycle. Through the catabolism of sugars, fats, and proteins, a two carbon organic product acetate in the form of acetyl-CoA is produced. One of the primary sources of acetyl-CoA is sugars that are broken down by glycolysis to produce pyruvate that, in turn, is decarboxylated by the enzyme pyruvate dehydrogenase.

This generates acetyl-CoA according to the following reaction scheme:. Privacy Policy. Skip to main content. Microbial Metabolism. Search for:. The Citric Acid Krebs Cycle. Learning Objectives List the steps of the Krebs or citric acid cycle. If there were no oxygen present in the mitochondrion, the electrons could not be removed from the system, and the entire electron transport chain would back up and stop.

The mitochondria would be unable to generate new ATP in this way, and the cell would ultimately die from lack of energy. This is the reason we must breathe to draw in new oxygen. In the electron transport chain, the free energy from the series of reactions just described is used to pump hydrogen ions across the membrane. Hydrogen ions diffuse through the inner membrane through an integral membrane protein called ATP synthase Figure 4.

This complex protein acts as a tiny generator, turned by the force of the hydrogen ions diffusing through it, down their electrochemical gradient from the intermembrane space, where there are many mutually repelling hydrogen ions to the matrix, where there are few. This flow of hydrogen ions across the membrane through ATP synthase is called chemiosmosis. Chemiosmosis Figure 4. The result of the reactions is the production of ATP from the energy of the electrons removed from hydrogen atoms.

These atoms were originally part of a glucose molecule. At the end of the electron transport system, the electrons are used to reduce an oxygen molecule to oxygen ions.

The extra electrons on the oxygen ions attract hydrogen ions protons from the surrounding medium, and water is formed. The electron transport chain and the production of ATP through chemiosmosis are collectively called oxidative phosphorylation.

The number of ATP molecules generated from the catabolism of glucose varies. For example, the number of hydrogen ions that the electron transport chain complexes can pump through the membrane varies between species. Another source of variance stems from the shuttle of electrons across the mitochondrial membrane. The NADH generated from glycolysis cannot easily enter mitochondria. Another factor that affects the yield of ATP molecules generated from glucose is that intermediate compounds in these pathways are used for other purposes.

Glucose catabolism connects with the pathways that build or break down all other biochemical compounds in cells, and the result is somewhat messier than the ideal situations described thus far.