March 28, 2023 8:49 pm

Is Krebs Cycle Aerobic Or Anaerobic? Why & How

As long as breathing gives your lungs the oxygen they need, you can continue an aerobic exercise routine. But once you start working out, your body can’t get enough oxygen to the intricate processes of aerobic metabolism quickly enough. As a result, the first few minutes are spent on anaerobic respiration.

The aerobic system predominately takes over as your body gets used to steady-state exercise. When the body generates energy from chemical reactions using oxygen, the process is called aerobic respiration, which literally means “with oxygen.” Aerobic metabolism includes the Krebs cycle.

A very difficult question is whether the Krebs cycle is aerobic or anaerobic. Since the Krebs cycle itself does not require oxygen, the process will stop if it is not provided. Therefore, we will find out whether the Krebs cycle is aerobic or anaerobic in this section.

No oxygen molecule itself is needed for the Krebs cycle process. But after ending when the reductant molecule undergoes an electron transport chain, O2 serves as the last electron acceptor. In absence of O2 the whole process along with a clogged Krebs cycle. That’s why though the Krebs cycle doesn’t require O2 itself, it is an aerobic respiration process.

Famous German biologist, and biochemists Sir Hans Adolf Krebs, and William Arthur Johnson first identified the process in 1937. According to Sir H. A. Krebs, the Krebs cycle is the name of the process. Because acetyl-CoA and oxaloacetate react at the start of this process to produce citric acid, the cycle is also known as the “citrus acid cycle.”

The six-carbon molecule of citric acid contains three carboxylic groups (-COOH). Because of this, the cycle is also known as the tricarboxylic acid cycle (TCA cycle). There are 8 enzyme-mediated reactions in the Krebs cycle. The enzymes involved in the Krebs cycle are Citrate synthase, aconitase, isocitrate dehydrogenase, α-ketoglutarate, succinyl-CoA synthetase, succinate dehydrogenase, fumarase, malate dehydrogenase, etc. are examples of these enzymes.

Krebs cycle also creates reductants, which later take part in the oxidative phosphorylation process, in addition to small amounts of energy. After completing one cycle 3 molecules of NADH, 1 molecule FADH2, 1 molecule GTP (or ATP), 2 molecules of CO2 are produced.

Does Krebs Cycle Occur in Anaerobic Respiration?

Despite not requiring oxygen, the Krebs cycle is only an aerobic respiration method.

Glycolysis is the first step in the anaerobic respiration process, just like aerobic respiration. In the glycolysis process, the sugar molecule splits into the 3-carbon pyruvate (C3H4O3) molecule and yields some energy (2 ATP). The reductant NADH then fails to undergo oxidative phosphorylation in anaerobic processes as a result of the lack of oxygen, and the Krebs cycle process is also impeded. Because of this, the Krebs cycle does not function in anaerobic mode.

The molecules go through lactic acid production or alcohol fermentation after the glycolysis process in anaerobic mode instead of the Krebs cycle, which releases little ATP (2 ATP).

The sugar molecule first goes through glycolysis to become pyruvate (C3H4O3), a three-carbon molecule, and then it breaks down again to produce lactic acid and energy.

C6H12O6 → C3H6O3 + energy (2ATP)

In the alcohol fermentation process the sugar molecule undergoes glycolysis and converts into three carbon molecule pyruvate (C3H4O3), after that it breaks and converts into alcohol (Ethanol) and produces energy and carbon dioxide (CO2).

C6H12O6 → C2H5OH + CO2 + energy (2ATP)

Krebs Cycle Steps

The pyruvate that is produced during glycolysis enters the mitochondrial matrix and is oxidized thereafter glycolysis, which is the first stage of respiration. It transforms into acetyl-CoA after releasing a carboxyl group as carbon dioxide. The only molecule that starts the Krebs cycle process is acetyl-CoA. Following a number of steps, the Krebs cycle continues.

  • Condensation between acetyl-CoA and oxaloacetate
  • Isomerization of citric acid
  • Decarboxylation of ispcitrate
  • Oxidative decarboxylation of α-ketoglutarate
  • succinyl-CoA to succinate
  • Dehydration of succinate
  • Hydration of fumarate
  • Dehydrogenation of L-malate

Is Krebs cycle aerobic or anaerobic from Wikimedia Commons

Condensation Between Acetyl-CoA and Oxaloacetate

Oxaloacetate (OAA) was initially linked to the acetyl-CoA that was produced by the oxidation of pyruvate. Citrate synthase participates in this irreversible reaction, which results in the formation of citrate and coA.

Isomerization of Citric Acid

The enzyme aconitase dehydrates citrate in a two-step reversible reaction, turning it into cis-aconitase. After the step, cis-aconitase goes through rehydration and creates isocitrate.

Decarboxylation of Isocitrate

It also involves two steps. At first, the isocitrate dehydrogenase enzyme converts isocitrate to oxalosuccinate and NAD+ into NADH.

Oxalosuccinate is transformed into α-ketoglutarate and one molecule of CO2 is released, which facilitates decarboxylation in the second step.

Oxidative Decarboxylation of α-ketoglutarate

It’s another oxidation-reduction reaction, like the one in the previous step. The conversion of α-ketoglutarate to succinyl-CoA by α-ketoglutarate dehydrogenase is an irreversible reaction that releases a carboxyl group or one molecule of CO2. One NADH molecule is created in this reaction.

Succinyl-CoA to Succinate

It is the only process in which guanosine diphosphate is phosphorylated to create GTP molecules. The enzyme succinyl-CoA synthase, which turns succinyl-CoA into succinate and generates GTP, makes this step easier.

Dehydration of Succinate

In this step succinate dehydrogenase, dehydrogenated succinate into the

FAD acts as an electron acceptor in this reaction, converting to FADH2. At the end, it generates two molecules of ATP after going through the electron transport chain.

Hydration of Fumarate

The reaction is reversible. L-malate is produced when fumarate is hydrated by the enzyme fumarase.

Dehydrogenation of L-malate

L-malate dehydrogenase plays a role in the oxidation-reduction reaction as well. The L-malate dehydrogenase turns L-malate into oxaloacetate and changes NAD+ into NADH reductant. It is the final stage of the cycle, after which the NADH contributes to the mechanism of the electron transport chain and generates energy. Oxaloacetate, in conjunction with acetyl-CoA, enables the cycle to be repeated once more.

At the final stage of aerobic respiration, the entire mechanism goes through oxidative phosphorylation and releases energy by dissolving bonds. The oxygen molecule functions as the final electron acceptor molecule in this process, which transforms NADH into NAD.

The oxidative phosphorylation process is not the Krebs cycle, and the two are not equivalent. At the conclusion of the Krebs cycle, oxidative phosphorylation takes place. Where the Krebs cycle produces Carbon Dioxide or CO2, Adenosine triphosphate (ATP) or Nicotinamide adenine dinucleotide (NADH), and flavin adenine dinucleotide (FAD) reductant. By converting NADH into NAD during the oxidative phosphorylation process, energy molecules or ATP are produced.

Krebs Cycle

Is Krebs Cycle Catabolic Or Anabolic?

Catabolic reactions are metabolic processes that result in the breakdown and conversion of complex molecules into smaller molecules and the release of energy. A metabolic process is an energy-intensive reaction in which simpler molecules are used to build larger, more complex molecules.

In the Krebs cycle, it is evident that the catabolic reaction results from the oxidation of acetyl-CoA, GTP, NADH, FADH2, etc. On the other hand, the reaction’s intermediates (citrate, alpha-ketoglutarate, and succinate) are employed in various mechanisms for the synthesis of complex molecules, such as anabolic reactions. It indicates that the Krebs cycle has both catabolic and anabolic properties, which is why it is known as an amphibolic reaction. Amphibolic reactions are those in which there are both anabolic and catabolic processes involved.

Is the Krebs Cycle Part of Photosynthesis?

The Krebs cycle is not involved in the photosynthesis process. The Krebs cycle takes place in the mitochondrial matrix of the cell as part of the cellular respiration process.

The Calvin Cycle, also known as the C3 cycle, takes place in the plant’s chloroplast during the photosynthesis process. This process converts CO2 or carbon dioxide into sugar or (C6H12O6) Glucose molecules

Overall, we can say that the Krebs cycle is one of the most significant amphibolic reactions in the aerobic respiration process.