Phases of Complete Glucose Breakdown

Cellular respiration involves a metabolic pathway of enzymes assisted by coenzymes.

The two coenzymes involved in cellular respiration, NAD+ and FAD, receive the hydrogen atoms removed from glucose. Glucose has 12 hydrogen atoms that will be pulled off one at a time and picked up by NAD+ or FAD.


7.2 Phases of Complete Glucose Breakdown

The complete oxidation of glucose involves four phases.

1. Glycolysis, the splitting of glucose into two 3-carbon molecules

2. The preparatory reaction, which divides each 3-carbon molecule into a 2-carbon molecule and CO2

3. The citric acid or Krebs cycle, which produces CO2, NADH, FADH2, and ATP

4. The electron transport chain also known as the electron transport system, assists in the production of the largest amount of ATP

7.3  Inside the Mitochondria

Except for glycolysis, the stages of ATP production occur in the mitochondria. The stages that occur in the mitochondrion are known as cellular respiration.

The last step (the electron transport system) require the presence of oxygen. 

The structure of mitochondria is important for them to work properly. The cristae provide extra surface area for the proteins (enzymes) of the ETS.


The Electron Transport Chain (or electron transport system)

The electron transport chain is located in the cristae of the mitochondria.

The members of the electron transport chain accept electrons from the hydrogen atoms carried by NADH and FADH2.

As the electrons are passed down the electron transport chain, energy is released and captured for ATP production.



At the end of the electron transport chain, the electrons are donated to oxygen atoms which combine with the hydrogens from NADH and FADH2 to form water. We breathe in order to have oxygen at the bottom of the ETS. Without it, cellular respiration cannot occur.


The Cristae of a Mitochondrion

The enzymes of the electron transport chain are imbedded in the cristae of the mitochondria in a specific pattern. This allows the high energy electrons to "fall" from one carrier to the next like a ball rolling down a set of stairs.


Energy Yield from Glucose Metabolism

The complete breakdown of one glucose yields 36 ATP molecules in eukaryotic organisms.


 Toggle open/close quiz question

The electron transport system requires oxygen in order to function properly.


Extra Help


An animation of the steps of cellular respiration