Link Reaction Between Glycolysis And Krebs Cycle: Diagrams, Equation & Steps

What Is Glycolysis And Kreb Cycle?

Glycolysis and the Krebs cycle are two dependent ways in cellular metabolic processes, relevant to cell respiration. The two processes are above all pathways in which the conversion of glucose occurs to generate usable energy in the form of ATP. Besides, glycolysis occurs in the cytoplasm, and the Krebs cycle occurs in the mitochondria. Elucidating how these two pathways relate to one another is key to understanding how it is that cells generate energy.

Overview Of Glycolysis

Glycolysis is a metabolic pathway that oxidizes glucose, a six-carbon sugar, into two molecules of pyruvate, a three-carbon compound, in the presence of an inorganic phosphate, a coenzyme of the B_vitamin niacin. In addition, this ten-step process takes place in the cytoplasm since it does not involve any oxygen molecules; hence, it is considered anaerobic. Glycolysis includes ten enzymatic reactions that eventually convert glucose into pyruvate and build a net gain of two ATP and two NADH molecules.

Steps

Energy Investment Phase:

This is where two molecules of ATP get used up in phosphorylating glucose and its derivatives to get them ready for a complete breakdown.

Energy Payoff Phase:

In this phase, four ATP molecules are produced when the glucose is converted into two molecules of pyruvate. In the overall accounting, the net gain from glycolysis is two ATP molecules because two were used in the investment phase.

Fate Of Pyruvate

After glycolysis has occurred, the direction that the pyruvate takes is determined by the conditions to which it is exposed:

Aerobic Conditions:

In the presence of oxygen, the pyruvate diffuses into the mitochondria where it is then oxidatively decarboxylated to acetyl-CoA. This process is catalyzed by the pyruvate dehydrogenase complex. Concomitantly, the coenzyme NAD+ to NADH is reduced and carbon dioxide is released.

Anaerobic Conditions:

In the absence of oxygen, the pyruvate is often converted to either lactic acid by fermentation in animal muscles or to ethanol and carbon dioxide in yeast fermentation processes.

The Krebs Cycle

The Krebs cycle involves a series of enzymatic reactions in the mitochondrial matrix, in which the reaction starts with condensation of acetyl-CoA with oxaloacetate into citrate. It involves several oxidations And decarboxylations of the compounds, which in the end lead to the reformation of oxaloacetate to start the cycle all over again.

Krebs Cycle Steps

The Krebs cycle can be summarized in the following steps:

1. Formation of Citrate: Acetyl-CoA combines with the oxaloacetate to produce citrate.

2. Isomerisation: Migration of the citrate mould to give isocitrate

3. Oxidative Decarboxylation: Loss of carbon from isocitrate to give alpha-ketoglutarate, with the generation of NADH (and carbon dioxide)

4. Further Decarboxylation: Conversion of alpha-ketoglutarate to succinyl-CoA, with the generation of another NADH (and carbon dioxide)

5. Substrate-level phosphorylation: Conversion of succinyl-CoA to succinate, with the creation of GTP (or ATP)

Linking Glycolysis And The Krebs Cycle

The link between glycolysis and the Krebs cycle is established through pyruvate-to-acetyl-CoA conversion. Therefore, this reaction links the two pathways, now allowing the products from glycolysis to move into the Krebs cycle for further energy extraction.

1. Glycolysis Produces Pyruvate: It converts glucose into pyruvate, which is the key intermediate linking the two pathways.

2. Conversion to Acetyl-CoA: In an aerobic environment, pyruvate first converts into acetyl-CoA that is located within the mitochondria and eventually goes into the Krebs cycle.

3. Energy Production: The responsibility of the Krebs cycle is that it will take the figure of acetyl-CoA to generate both NADH and FADH2 that are needed for the electron transport chain and ATP synthesis, respectively.

Regulation Of The Pathways

To maintain homeostasis in cell energy, both the glycolytic pathway and the Krebs cycle are highly regulated. The key regulation of these two pathways is shown below:

1. Hexokinase and phosphofructokinase during glycolysis, are influenced by ATP, ADP, and other metabolites; II.

2. Pyruvate dehydrogenase linking glycolysis to the Krebs cycle, controlled by the availability of substrates and products; III.

3. Isocitrate dehydrogenase and α-ketoglutarate dehydrogenases in the Krebs cycle, which respond to energy levels within the cell.

Glycolysis And Krebs Cycle: Their Significance

The role of both glycolysis and the Krebs cycle in cellular respiration is one of collaboration. The pathways, aside from their ATP generation, also provide intermediates for many biosynthetic pathways. Any failures in these pathways will surely lead to disturbances in metabolic activity and hence affect overall cell function.

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