Aerobic Cellular Respiration, by Mikael Häggström

Why Do We Breathe? 
The Steps of Aerobic Cellular Respiration 

CLASS NOTES from Science Prof Online


The reactions of cellular respiration occur as four subpathways, which include:

  •   glycolysis
  •   synthesis of Acetyl-CoA
  •   Krebs cycle

The first step, glycolysis, occurs in cytoplasm of most cells, and the word itself describes the process-'glyco' = sugar and 'lysis' = breaking down. 
Article Summary: Aerobic cellular respiration is the series of reactions that, with the help of oxygen, make ATP (cellular energy) by completely breaking down glucose into inorganic molecules of carbon dioxide and water. 
Metabolism of Turning Food into ATP Energy in Living Cells
Molecular Oxygen (a.k.a. Dioxygen)
Molecular oxygen: 1/2 O2 is the final electron acceptor of the end of the electron transport chain.
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Endomembrane System of a Eukaryotic Cell, Mariana Ruiz
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Portions of this article originally appeared on Suite101 online magazine.​

​Page last updated: 5/2013

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Glycolysis involves the splitting of a six-carbon glucose into two three-carbon molecules of pyruvic acid, and results in a net production of two molecules of ATP.

Synthesis of Acetyl-CoA
Pyruvic acid is then transformed into the molecule acetyl-CoA. This is one of the cellular respiration reactions that produces CO2, the gas that we breathe out when we exhale. In addition to acetyl-CoA and CO2 waste, two molecules of the electron carrier NADH are produced. The energy of electron carriers will be used later, during electron transport.

Kreb's Cycle
Also known as the Citric Acid Cycle, this complex series of reactions transfers much of the energy left in the bonds of acetyl-CoA to more electron carriers (NAD+ and FAD). The reactions of Krebs Cycle occur in the mitochondria of eukaryotes and result in two more molecules of ATP, two molecules of FADH2, six molecules of NADH, and more CO2 waste.

Electron Transport Chain
The most significant production of ATP occurs through a stepwise release of energy from the series of oxidation-reduction reactions in the electron transport chain.

The electron transport chain consists of several membrane-bound carrier molecules that pass electrons from one to another and ultimately to final electron acceptor, oxygen (O2). We need to breathe in oxygen in order to complete electron transport.

Energy from electrons is used to pump protons (H+) across the inner membrane of the mitochondria, establishing a proton gradient, a difference in ion concentration on either side of a membrane. Proton gradients have potential energy available for cellular work.

Protons flow down this gradient, through protein channels that phosphorylate adenosine diphosphate (ADP), adding energy to create adensoine triphosphate ATP.

By the end of aerobic cellular respiration, a total of 38 molecules of ATP are formed from one molecule of glucose.

  • Bauman, R. (2005) Microbiology. Pearson Benjamin Cummings.
  • Park Talaro, K. (2008) Foundations in Microbiology. 

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