The other names for the Krebs cycle are citric acid cycle because the citric acid is both the first product and the final reactant and tricarboxylic acid cycle because of the involvement of the three carboxyl groups. In particular, the Krebs cycle is one of the major metabolic pathways of cellular respiration. It involves a cyclic series of enzymatic reactions through which pyruvate — converted into Acetyl Coenzyme A — is completely oxidized to CO 2.
Along with this, hydrogen ion is removed from the carbon molecules, transferring the hydrogen atoms and electrons to electron-carrier molecules e. The carbon dioxide produced from the complete oxidation of pyruvate is removed from the cell into the blood.
The electron and hydrogen carriers, NADH and FADH 2 , donate these electrons to the electron transport chain to generate ATP via oxidative phosphorylation , the final metabolic pathway of cellular respiration.
In eukaryotes the Krebs Cycle occurs in the matrix of the mitochondrion whereas in prokaryotes , it occurs in the cytoplasm. Word origin: named after Hans Adolf Krebs, first described it in Synonym s :. Plants are responsible for incredible feats of molecular transformation. Plant processes, such as photosynthesis, photophosphorylation, chemiosmosis, carbon fixing reactions, respiration, are presented in this tutorial Read More.
Proteins have a crucial role in various biological activities. Steps 3 and 4. CoA binds the succinyl group to form succinyl CoA. Step 5. A phosphate group is substituted for coenzyme A, and a high- energy bond is formed.
This energy is used in substrate-level phosphorylation during the conversion of the succinyl group to succinate to form either guanine triphosphate GTP or ATP. There are two forms of the enzyme, called isoenzymes, for this step, depending upon the type of animal tissue in which they are found.
One form is found in tissues that use large amounts of ATP, such as heart and skeletal muscle. This form produces ATP. The second form of the enzyme is found in tissues that have a high number of anabolic pathways, such as liver. This form produces GTP. In particular, protein synthesis primarily uses GTP. Step 6. Step six is a dehydration process that converts succinate into fumarate. Unlike NADH, this carrier remains attached to the enzyme and transfers the electrons to the electron transport chain directly.
This process is made possible by the localization of the enzyme catalyzing this step inside the inner membrane of the mitochondrion. Step 7. Water is added to fumarate during step seven, and malate is produced. The last step in the citric acid cycle regenerates oxaloacetate by oxidizing malate. Another molecule of NADH is produced.
Two carbon atoms come into the citric acid cycle from each acetyl group, representing four out of the six carbons of one glucose molecule. Two carbon dioxide molecules are released on each turn of the cycle; however, these do not necessarily contain the most recently-added carbon atoms.
The two acetyl carbon atoms will eventually be released on later turns of the cycle; thus, all six carbon atoms from the original glucose molecule are eventually incorporated into carbon dioxide. These carriers will connect with the last portion of aerobic respiration to produce ATP molecules. Several of the intermediate compounds in the citric acid cycle can be used in synthesizing non-essential amino acids; therefore, the cycle is amphibolic both catabolic and anabolic.
In order for pyruvate, the product of glycolysis, to enter the next pathway, it must undergo several changes to become acetyl Coenzyme A acetyl CoA. Acetyl CoA is a molecule that is further converted to oxaloacetate, which enters the citric acid cycle Krebs cycle.
The conversion of pyruvate to acetyl CoA is a three-step process. Breakdown of Pyruvate : Each pyruvate molecule loses a carboxylic group in the form of carbon dioxide.
A carboxyl group is removed from pyruvate, releasing a molecule of carbon dioxide into the surrounding medium. Note: carbon dioxide is one carbon attached to two oxygen atoms and is one of the major end products of cellular respiration. The result of this step is a two-carbon hydroxyethyl group bound to the enzyme pyruvate dehydrogenase; the lost carbon dioxide is the first of the six carbons from the original glucose molecule to be removed.
This step proceeds twice for every molecule of glucose metabolized remember: there are two pyruvate molecules produced at the end of glycolysis ; thus, two of the six carbons will have been removed at the end of both of these steps. Step 3. The enzyme-bound acetyl group is transferred to CoA, producing a molecule of acetyl CoA. 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.
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