An Explanation of The Process of Cellular Respiration

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2 pages /

1021 words

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1021 words

Downloads: 37

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Table of contents

  1. Cellular Respiration (Aerobic Respiration)
  2. Glycolysis
  3. Transformation of pyruvate
  4. Krebs cycle (The citric acid cycle)
  5. Steps of the Krebs cycle
  6. Conclusion

Respiration is the chemical process by which organic compounds release energy. The compounds change into different ones by exergonic reactions. There are two types of respiration:

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  • Aerobic, needs oxygen and releases a lot of energy;
  • Anaerobic, which does not require oxygen but releases much less energy per mole of starting material.

Cellular Respiration (Aerobic Respiration)

Cellular respiration is the process by which individual cells break down food molecules, such as glucose and release energy. This is because cellular respiration slowly releases the energy of glucose in a few small steps. It uses the energy released to form ATP molecules, which are the energy-carrying molecules that cells use to power biochemical processes. Cellular respiration involves many chemical reactions and it is an aerobic process because oxygen is required for cellular respiration.

Cellular respiration reactions can be divided into three main stages and intermediate stages:

  • Glycolysis
  • Transformation of pyruvate
  • Krebs cycle ( The citric acid cycle)
  • Oxidative phosphorylation


Glycolysis occurs in the cytoplasm of a cell where a 6 carbon glucose molecule is broken down by enzymes into a 3 carbon pyruvic acid. The execution of this process requires 2 ATP and produces a net gain of 2 ATP. The enzyme that binds removes hydrogen from glucose (oxidation), where it carries the hydrogen atoms to the cytochrome system. In anaerobic respiration, this is where the process ends; glucose is split into 2 molecules of pyruvic acid. When oxygen is present, pyruvic is broken down into other carbon compounds in the Kreb’s Cycle. When it is not present, the pyruvic acid is broken down into lactic acid High-energy electrons are also transferred to energy-carrying molecules called electron carriers through the process known as reduction. The electron carrier of glycolysis is NAD (nicotinamide adenine diphosphate). Electrons are transferred to 2 NAD to produce two molecules of NADH.

Transformation of pyruvate

Pyruvate is a pivotal metabolite in cellular respiration. Each pyruvate from glycolysis goes into the mitochondrial matrix the innermost compartment of mitochondria. There, it’s converted into a two-carbon molecule bound to Coenzyme A, known as acetyl CoA. Carbon dioxide is released and NADH is generated.

Krebs cycle (The citric acid cycle)

Mitochondria have an inner and outer membrane. The space between the inner and outer membrane is called the intermembrane space. The space around the inner membrane is called the matrix. The Krebs cycle, the second stage of cellular respiration, occurs in the matrix. The third stage, electron transport, takes place on the inner membrane. Glycolysis produces two molecules of pyruvate. These molecules enter the mitochondrial matrix, where the Krebs cycle begins.

Steps of the Krebs cycle

The Krebs cycle (which is also known as the TCA cycle, or citric acid, cycle) plays a central role in the breakdown of organic fuel molecules. The cycle is made up of eight steps catalyzed by eight different enzymes that produce energy at several different stages. Most of the energy obtained from the Krebs cycle, however, is captured by the compounds NAD and FAD and converted later to ATP. The products of a single turn of the Krebs cycle consist of three NAD molecules, which are reduced to the same number of NADH molecules, and one FAD molecule, which is similarly reduced to a single FADH2 molecule. These molecules go on to fuel the third stage of cellular respiration, whereas carbon dioxide, which is also produced by the Krebs cycle, is released as a waste product.

After the second turn through the Krebs cycle, the original glucose molecule has been broken down completely. All six of its carbon atoms have combined with oxygen to form carbon dioxide. The energy from its chemical bonds has been stored in a total of 16 energy-carrier molecules.

Oxidative phosphorylation is the final stage of atmospheric cell respiration. Oxidative phosphorylation has two substrates, the Electron transport chain and the Chemiosmosis. In these cases, energy from NADH and FADH2, a by-product of the earlier stages of cellular respiration, is used to form ATP.

In this case, the high-energy electrons are released from NADH and FADH2 and travel along the electron-transport chains in the mitochondrial endothelium. An electron-transport chain is a series of molecules that transfer electrons from molecule to molecule by chemical reactions. These molecules are found making up the three complexes of the electron transport chain and an accessory complex. As electrons flow through these molecules, some of the energy from the electrons is used to pump H ions across the inner membrane, from the matrix into the intermembrane space. This ion transfer creates an electrochemical gradient that drives the synthesis of ATP.

The pumping of hydrogen ions across the inner membrane creates a greater concentration of these ions in the intermembrane space than in the matrix – producing an electrochemical gradient. This gradient causes the ions to flow back across the membrane into the matrix, where their concentration is lower. The flow of these ions occurs through a protein complex, known as the ATP synthase complex. The ATP synthase acts as a channel protein, helping the hydrogen ions across the membrane. It also acts as an enzyme, forming ATP from ADP and inorganic phosphate. It is the flow of hydrogen ions through ATP synthase that gives the energy for ATP synthesis. After passing through the electron-transport chain, the low-energy electrons combine with oxygen to form water.

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Respiration involves the participation of different processes responsible for the oxidation of glucose molecules for energy and C structures, either in the aerobic or anaerobic of oxygen. In the latter case, the most affected organ is the root, inducing partial oxidation strategies of substrates in order to continue to generate energy without oxygen. These strategies are called fermentation, which differentiate themselves by their end products: ethanol, lactic acid and alanine. In the presence of O2, substrates are completely oxidized to CO2 and H2O. This is done through three metabolic processes: glycolysis, the TCA cycle and the OXPHOS. To these is added a fourth process; transport of the products of respiration. This corresponds to the movement of substrates and cofactors to facilitate the release of products throughout the cell. The operation of these processes is the most efficient way to obtain energy from complete oxidation of hydrocarbon substrates, both in plants and animals.

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An Explanation of the Process of Cellular Respiration. (2022, May 24). GradesFixer. Retrieved September 21, 2023, from
“An Explanation of the Process of Cellular Respiration.” GradesFixer, 24 May 2022,
An Explanation of the Process of Cellular Respiration. [online]. Available at: <> [Accessed 21 Sept. 2023].
An Explanation of the Process of Cellular Respiration [Internet]. GradesFixer. 2022 May 24 [cited 2023 Sept 21]. Available from:
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