• The citric acid cycle begins with the transfer of a two-carbon acetyl group from acetyl-CoA to the four-carbon acceptor compound (oxaloacetate) to form a six-carbon compound (citrate).
• The citrate then goes through a series of chemical transformations, losing two carboxyl groups as CO₂. The carbons lost as CO₂ originate from what was oxaloacetate, not directly from acetyl-CoA. The carbons donated by acetyl-CoA become part of the oxaloacetate carbon backbone after the first turn of the citric acid cycle. Loss of the acetyl-CoA-donated carbons as CO₂ requires several turns of the citric acid cycle. However, because of the role of the citric acid cycle in anabolism, they may not be lost, since many TCA cycle intermediates are also used as precursors for the biosynthesis of other molecules.^[6]
• Most of the energy made available by the oxidative steps of the cycle is transferred as energy-rich electrons to NAD⁺, forming NADH. For each acetyl group that enters the citric acid cycle, three molecules of NADH are produced.
• Electrons are also transferred to the electron acceptor Q, forming QH₂.
• At the end of each cycle, the four-carbon oxaloacetate has been regenerated, and the cycle continues.

Krebs cycle

Krebs cycle or the citric acid cycle or tricarboxylic acid cycle,occurs in mitochondria, is the common pathway to completely oxidize fuel molecules which mostly is acetyl CoA ,the product from the oxidative decarboxylation of pyruvate.It enters the cycle and passes ten steps of reactions that yield energy and CO2
You can browse the ten steps of reactions through three strands: fact sheet gives the name of enzyme, reaction type,mechanism and prosthetic group; reaction shows the structure of substrate and product(s) and animation presents a short movie clip showing the reaction.
Before going through the TCA cycle, you should know about the oxidative decarboxylation of pyruvate. This reaction links between Glycolysis and TCA cycle.

http://highered.mcgrThe Krebs cycle refers to a complex series of chemical reactions in all cells that utilize oxygen as part of their respiration process. This includes those cells of creatures from the higher animal kingdom, such as humans. The Krebs cycle produces carbon dioxide and a compound rich in energy, Adenosine tri-phosphate (ATP). This chemical provides cells with the energy required for the synthesis of proteins from amino acids and the replication of deoxyribonucleic acid (DNA).

The Krebs cycle, also known as the tri-carboxylic acid cycle (TCA), was first recognized in 1937 by the man for whom it is named, German biochemist Hans Adolph Krebs. His highly detailed and extensive research in the field of cellular metabolism and other scientific endeavors gleaned him the Nobel Prize for Physiology or Medicine in 1953. In short, the Krebs cycle constitutes the discovery of the major source of energy in all living organisms.

Within the Krebs cycle, energy in the form of ATP is usually derived from the breakdown of glucose, although fats and proteins can also be utilized as energy sources. Since glucose can pass through cell membranes, it transports energy from one part of the body to another. The Krebs cycle affects all types of life and is, as such, the metabolic pathway within the cells. This pathway chemically converts carbohydrates, fats, and proteins into carbon dioxide, and converts water into serviceable energy.

http://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter25/animation__how_the_krebs_cycle_works__quiz_1_.html

Look at this link for more clarity.

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