What is the Krebs Cycle?

Answer 1

In the presence of oxygen, pyruvic acid produced in glycolysis is passed to the second stage of cellular respiration, The Krebs Cycle. During the Krebs Cycle, pyruvic acid is broken into carbon dioxide in a series of energy extracting reactions.
You mean the Krebs Cycle. It is a series of chemical reactions in a cell, arranged like a circular bucket brigade in which pyruvate is degraded in steps and the energy at each step transferred to ATP.

Answer 2

The Kreb Cycle is a series of chemical reactions carried out in the living cell identified by Hans Adolf Kreb.

The citric acid cycle - also known as the tricarboxylic acid cycle (TCA cycle), the Krebs cycle, or more rarely, the Szent-Györgyi-Krebs cycle, is a series of enzyme-catalysed chemical reactions, which is of central importance in all living cells that use oxygen as part of cellular respiration. In cells with nuclei (eukaryotes), the citric acid cycle occurs in the matrix of the mitochondrion. The components and reactions of the citric acid cycle were established by seminal work from Albert Szent-Györgyi and Hans Krebs.

In aerobic organisms, the citric acid cycle is part of a metabolic pathway involved in the chemical conversion of carbohydrates, fats and proteins into carbon dioxide and water to generate a form of usable energy. Other relevant reactions in the pathway include those in glycolysis and pyruvate oxidation before the citric acid cycle, and oxidative phosphorylation after it. In addition, it provides precursors for many compounds including some amino acids and is therefore functional even in cells performing fermentation.

· The citric acid cycle begins with acetyl-CoA transferring its two-carbon acetyl group 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.

· 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

The total number of ATP obtained after complete oxidation of one glucose in glycolysis, citric acid cycle, and oxidative phosphorylation is estimated to be between 30 and 38. A recent assessment of the total ATP yield with the updated proton-to-ATP ratios provides an estimate of 29.85 ATP per glucose molecule.

Answer 3

The Kreb's cycle (aka. citric acid cycle, tricarboxylic acid cycle) is part of the cellular respiration of a cell. The end result of this pathway are 4xNADH, 1xFADH2, and 1 ATP. NADH and FADH2 are used later in the electric transport chains to further produce ATP. ATP is the energy currency of all cells.

Some textbooks label different amount of reactions but the cycle is all the same.

X. substrate -- (enzyme) --> product

1. Acetyl CoA --(citrate synthase)--> Citrate

2. Citrate --(aconitase)--> Cis-aconitate

3. Cis-aconitate --(aconitase)--> Isocitrate

4. Isocitrate --(isocitrate dehydrogenase)--> Oxalosuccinate

5. Oxalosuccinate --(isocitrate dehydrogenase)--> alpha-Ketoglutarate

6. alpha-Ketoglutrate --(alpha-ketoglutrate dehydrogenase)--> Succinyl-CoA

7. Succinyl-CoA --(succinate thiokinase)--> Succinate

8. Succinate --(succinate dehydrogenase)--> Fumarate

9. Fumarate --(fumarase)--> L-Malate

10. L-Malate --(malate dehydrogenase)--> Oxoacetate

It is called a cycle because oxoacetate is recycled back into citrate. There are a few level of regulation within this cycle. One is at citrate synthase. ADP will increase this enzyme activity and (NADH, succinyl CoA, ATP, Citrate) will act as inhibitors. Also for isocitrate dehydrogenase, ATP will decrease this enzyme activity and calcium/ADP will inhibit. Lastly, calcium will increase succinyl-CoA activity while succinyl-CoA and NADH will act inhibitory