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Overview of the citric acid cycle. The citric acid cycle—also known as the Krebs cycle, Szent–Györgyi–Krebs cycle, or TCA cycle (tricarboxylic acid cycle) [1] [2] —is a series of biochemical reactions to release the energy stored in nutrients through the oxidation of acetyl-CoA derived from carbohydrates, fats, proteins, and alcohol.
Malate, in the mitochondrial matrix, can be used to make pyruvate (catalyzed by malic enzyme) or oxaloacetic acid, both of which can enter the citric acid cycle. Glutamine can also be used to produce oxaloacetate during anaplerotic reactions in various cell types through "glutaminolysis", which is also seen in many c-Myc transformed cells. [3]
Two low-energy waste products, H 2 O and CO 2, are created during this cycle. [9] [10] The citric acid cycle is an 8-step process involving 18 different enzymes and co-enzymes. During the cycle, acetyl-CoA (2 carbons) + oxaloacetate (4 carbons) yields citrate (6 carbons), which is rearranged to a more reactive form called isocitrate (6 carbons).
Amphibolic properties of the citric acid cycle. An amphibolic pathway is one that can be either catabolic or anabolic based on the availability of or the need for energy. [10]: 570 The currency of energy in a biological cell is adenosine triphosphate (ATP), which stores its energy in the phosphoanhydride bonds. The energy is utilized to conduct ...
The citric acid cycle is a series of enzymatic reactions carried out inside the inner membranes of the cell's mitochondria. The process begins when the two-carbon acetyl CoA enters the cycle and joins the four-carbon oxaloacetate to produce the six-carbon citrate.
Oxidative phosphorylation contributes the majority of the ATP produced, compared to glycolysis and the Krebs cycle. While the ATP count is glycolysis and the Krebs cycle is two ATP molecules, the electron transport chain contributes, at most, twenty-eight ATP molecules. A contributing factor is due to the energy potentials of NADH and FADH 2.
Examples of catabolic processes include glycolysis, the citric acid cycle, the breakdown of muscle protein in order to use amino acids as substrates for gluconeogenesis, the breakdown of fat in adipose tissue to fatty acids, and oxidative deamination of neurotransmitters by monoamine oxidase.
Citric acid is an organic compound with the formula H O C(CO 2 H)(CH 2 CO 2 H) 2. [10] It is a colorless weak organic acid. [10] It occurs naturally in citrus fruits. In biochemistry, it is an intermediate in the citric acid cycle, which occurs in the metabolism of all aerobic organisms. [10] More than two million tons of citric acid are ...