Difference Between Ubiquinones and Cytochromes

The key difference between Ubiquinones and Cytochromes is that the Ubiquinones (CoQ) are not proteins while the Cytochromes are proteins.

Electron transport chain is the final stage of aerobic respiration. Therefore, it occurs in the inner membrane of mitochondria. Moreover, it consists of electron carriers that facilitate the production of a proton gradient across the membrane. Other than NAD and flavoproteins, Ubiquinones and Cytochromes are two types of electron carriers involved in the electron transport chain. Ubiquinones are non-protein lipid soluble, hydrophobic organic molecules whereas cytochromes are iron-containing proteins.

CONTENTS

1. Overview and Key Difference
2. What are Ubiquinones
3. What are Cytochromes
4. Similarities Between Ubiquinones and Cytochromes
5. Side by Side Comparison – Ubiquinones vs Cytochromes in Tabular Form
6. Summary

What are Ubiquinones?

Ubiquinones (Coenzyme Q) are small lipid-soluble organic molecules found in the inner mitochondrial membrane. Howver, they are not protein molecules, and they do not contain heme groups, instead they work as electron carriers in the electron transport chain. Ubiquinone accepts electrons from NADH reductase and passes to cytochrome for further transportation.

Ubiquinones are lipid soluble and hydrophobic. Hence, they can freely diffuse within the membrane and act as efficient electron carriers. When ubiquinone accepts one electron, it becomes semiquinone, and when accepts two electrons it becomes ubiquinol.

What are Cytochromes?

Cytochromes are a protein complex that acts as an electron carrier in electron transport chain. Therefore, they are loosely associated with the inner membrane of the mitochondria. Moreover, they are small heme proteins. Cytochromes serve as extreme important electron carriers since they facilitate the handover of electrons to a final electron acceptor (O₂) to complete respiration.

Moreover, there are three main cytochromes namely cytochrome reductase, cytochrome c and cytochrome oxidase. Cytochrome reductase receives electrons from ubiquinone and transfers to cytochrome c. Thereafter, cytochrome c transfers an electron to cytochrome oxidase. Finally, cytochrome oxidase passes electrons to O₂ (the final electron acceptor). When electrons travel through electron carriers, a proton gradient will create, and it will help for the ATP production.

What are the Similarities Between Ubiquinones and Cytochromes?

• Ubiquinones and Cytochromes are electron carriers.
• Both are associated with the inner membrane of mitochondria.
• They are necessary for ATP synthesis.
• They are able to accept as well as transfer electrons.

What is the Difference Between Ubiquinones and Cytochromes?

Ubiquinones and Cytochromes are two efficient and important electron carriers in the process of respiration. Ubiquinones are lipid soluble, hydrophobic small organic molecules. On the other hand, cytochromes are heme-containing protein molecules. This is the key difference between Ubiquinones and Cytochromes. Furthermore, both can accept and transfer electrons. But, ubiquinones accept an electron from NADH-Q reductase and hand over to cytochrome while cytochromes accept electrons from ubiquinones and transfer to oxygen.

Summary – Ubiquinones vs Cytochromes

Different types of electron carriers involve with electron transport chain or the oxidative phosphorylation process. Among them, ubiquinones and cytochromes are of two types. They are essential components of this process. Ubiquinones are small lipid soluble, hydrophobic molecules. Cytochromes are proteins that contain iron molecules along with them. This is the difference between ubiquinones and cytochromes.

Reference:

1.“Cytochromes.” Egyptian Journal of Medical Human Genetics, Elsevier. Available here 

Image Courtesy:

1.’Coenzymeq’By The original uploader was NicolasGrandjean at French Wikipedia. – Transferred from fr.wikipedia to Commons by Bloody-libu using CommonsHelper., (CC BY-SA 3.0) via Commons Wikimedia  
2.’Cytochrome c’By Klaus Hoffmeier – Own work, (Public Domain) via Commons Wikimedia