Krebs Cycle

Krebs Cycle

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In respiration, which can happen with or without oxygen, the first step is glycolysis. This is where glucose is broken down into two 3-carbon molecules called pyruvate. In anaerobic respiration, pyruvate turns into ATP through fermentation. In aerobic respiration, which produces a lot more ATP, pyruvate needs further reactions to release all of that energy. Two of these reactions are called the link reaction and the Krebs cycle.

The link reaction is a process that converts pyruvate into acetyl-coenzyme A (acetyl CoA). This happens right after glycolysis. The Krebs cycle then uses acetyl CoA to extract ATP through a series of reactions. The cycle is regenerative and produces important biomolecules for cells.

The Krebs cycle is also known as the TCA cycle or citric acid cycle and was named after the British biochemist Hans Krebs who discovered the sequence. To summarise, the Krebs cycle is a vital part of the respiration process that extracts energy from pyruvate to create ATP, and is made up of the link reaction and the Krebs cycle itself.

Where do the link reaction and Krebs cycle take place?

The link reaction and the Krebs cycle occur in a cell's mitochondria. As you will see in figure 2 below, the mitochondria contain a structure of folds within their inner membrane. This is called the mitochondrial matrix and has a range of compounds such as the mitochondria's DNA, ribosomes, and soluble enzymes. After glycolysis, which occurs before the link reaction, pyruvate molecules are transported into the mitochondrial matrix via active transport (active loading of pyruvate requiring ATP). These pyruvate molecules undergo the link reaction and the Krebs cycle within this matrix structure.

What are the different steps of the link reaction?

Pyruvate is transported from the cell's cytoplasm to the mitochondria via active transport. The link reaction then takes place, which consists of three steps: oxidation, dehydrogenation, and formation of acetyl CoA. Oxidation involves the decarboxylation of pyruvate, which results in the removal of a carbon dioxide molecule and the formation of a 2-carbon molecule called acetate. Dehydrogenation involves the loss of a hydrogen molecule accepted by NAD+ to produce NADH. Finally, acetate combines with coenzyme A to produce acetyl Co for the link reaction is: Pyruvate + Coenzyme A → Acetyl CoA + Carbon Dioxide + NADH + H+ .

What does the link reaction produce?

During aerobic respiration, for every glucose molecule broken down, the link reaction produces two molecules of carbon dioxide, two acetyl CoA molecules, and two NADH molecules, which stay in the mitochondrial matrix for the Krebs cycle. It is important to note that no ATP is produced during the link reaction, instead ATP is produced during the Krebs cycle.

The Krebs cycle occurs in the mitochondrial matrix and involves acetyl Co a into a 4bon molecule, which then combines with another molecule of acetyl CoA, forming a cycle. This cycle produces carbon dioxide, NADH, ATP, and reduced FAD as by-products.

The steps of the Krebs cycle are as follows:

  1. Formation of a 6-carbon molecule: Acetyl CoA, a 2-carbon molecule, combines with oxaloacetate, a 4-carbon molecule, forming citrate, a 6-carbon molecule. Coenzyme A is lost and exits the reaction as a by-product when citrate is formed.
  2. Formation of a 5-carbon molecule: Citrate is converted into a 5-carbon molecule called alpha-ketoglutarate. NAD+ is reduced to NADH, and carbon dioxide is formed as a by-product and exits the reaction.
  3. Formation of a 4-carbon molecule: Alpha-ketoglutarate is converted back into the 4-carbon molecule oxaloacetate through a series of different reactions. It loses another carbon, which exits the reaction as carbon dioxide. During these different reactions, two more molecules of NAD+ are reduced to NADH, one molecule of FAD is converted to reduced FAD, and one molecule of ATP is formed from ADP and inorganic phosphate.
  4. Regeneration: Oxaloacetate, which has been regenerated, combines Co, and

Overall, the Krebs cycle is an part res, producing NADH, ATP, and reduced FAD, which are used to generate energy for the cell.

What does the Krebs cycle produce?

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Overall, for every molecule of acetyl CoA, the Krebs cycle produces three molecules of NADH, one molecule of reduced FAD, one molecule of ATP, and two molecules of carbon dioxide. These by-products are important for the electron transport chain during oxidative phosphorylation and for fueling vital biochemical processes in the cell.

The link reaction is a process that oxidizes pyruvate to produce a compound called acetyl-coenzyme A (acetylA). occurs straight glyysis and produces two molecules of carbon dioxide, two acetyl CoA molecules, and two NADH molecules.

The Krebs cycle is a process that primarily exists to extract ATP from acetyl CoA through a series of oxidation-reduction reactions. Like the Calvin cycle in photosynthesis, the Krebs cycle is regenerative and provides a range of intermediate compounds used by cells to create a range of important biomolecules. Overall, every Krebs cycle produces one molecule of ATP, two molecules of carbon dioxide, one molecule of FAD, and three molecules of NADH.

Krebs Cycle

Where does the Krebs cycle take place?

The Krebs cycle takes place in the cell’s mitochondrial matrix. The mitochondrial matrix is found in the inner membrane of the mitochondria. 

How many ATP molecules are made in the Krebs cycle?

For every molecule of acetyl CoA produced during the link reaction, one molecule of ATP is produced during the Krebs cycle.

How many NADH molecules are produced in the Krebs cycle?

For every molecule of acetyl CoA produced during the link reaction, three molecules of NADH are produced during the Krebs cycle. 

What is the primary purpose of the Krebs cycle?

The main purpose of the krebs cycle is to produce energy, which is formed as ATP. ATP is a vital source of chemical energy which is used to fuel a range of biochemical reactions in the cell. 

What are the different steps of the Krebs cycle?

Step 1: Condensation of acetyl CoA with oxaloacetateStep 2: Isomerisation of citrate into isocitrateStep 3: Oxidative decarboxylations of isocitrateStep 4: Oxidative decarboxylation of α-ketoglutarateStep 5: Conversion of succinyl-CoA into succinateStep 6: Dehydration of succinate to fumarateStep 7: Hydration of fumarate to malateStep 8: Dehydrogenation of L-malate to oxaloacetate

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