FADH2 & NADH: Definition & Overview

FADH2 & NADH: Definition & Overview
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  • 0:01 Overview of Cellular…
  • 0:40 What Are FADH & NADH?
  • 1:16 Functions
  • 2:56 Lesson Summary
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Lesson Transcript
Instructor: Jeremy Battista
In this lesson, we take a closer look at some of the materials and mechanisms used in cellular respiration. As this is a very complex process, we will specifically focus on FADH2 and NADH.

Overview of Cellular Respiration

Cellular respiration is the process of utilizing oxygen and food molecules to create energy, carbon dioxide, water, and waste products. Basically, respiration is how we convert food into energy using water and oxygen. Respiration consists of three separate metabolic phases: glycolysis, the Krebs cycle, and the electron transport chain. We will not be going into any great detail on these three phases here. Instead, we'll be focusing on two compounds, FADH2 and NADH, and how they are incorporated into respiration.

What Are FADH2 and NADH?

Flavin adenine dinucleotide, or FADH2, is a redox cofactor that is created during the Krebs cycle and utilized during the last part of respiration, the electron transport chain. Nicotinamide adenine dinucleotide, or NADH, is a similar compound used more actively in the electron transport chain as well. In fact, more NADH is produced and used than FADH2 in the process of creating energy. There are actually six NADH produced and only two FADH2 molecules.


FADH2 and NADH are created from FAD and NAD+ through reduction-oxidation reactions in the Krebs cycle during respiration as seen below:

This cycle gives off small amounts of energy in the form of adenosine triphosphate, or ATP, and produces these compounds, FADH2 and NADH. The Krebs cycle is like a wheel. Every time it makes one full rotation, energy is created and released. As you can see from the diagram, the NAD+ and FAD are brought in at key points throughout the cycle and are attached to other electrons resulting in the formation of NADH and FADH2.

This energy is then shuttled off to be used by the cell, mostly for the continuation of cellular respiration.

As they are shuttled away, these two compounds are used to move electrons into the electron transport chain, the final stage of respiration. It is in this stage that most of the energy is created and released from the mitochondria (powerhouse of the cell).

Basically, the NADH and FADH2 molecules are affixed with electrons and are transferred to the inner membrane of the mitochondria. They travel down the electron transport chain, releasing the electrons that they once had. The end result is loads of energy, approximately 34 ATP (energy molecule).

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