What is the Difference Between Ubiquinone and Plastoquinone

The key difference between ubiquinone and plastoquinone is that ubiquinone is present in the inner membrane of mitochondria while plastoquinone is present in the thylakoids of chloroplast.

Ubiquinone and plastoquinone are two important prenylquinones that function as electron transporters in the electron transport chain of oxygenic photosynthesis and aerobic respiration, respectively. Both play an important role in plant growth and development, aiding in plant metabolism and biosynthesis processes.

CONTENTS

1. Overview and Key Difference
2. What is Ubiquinone
3. What is Plastoquinone
4. Similarities – Ubiquinone and Plastoquinone
5. Ubiquinone vs Plastoquinone in Tabular Form
6. Summary – Ubiquinone vs Plastoquinone

What is Ubiquinone?

Ubiquinone is a type of prenylquinone that acts as an electron carrier in the process of oxidative phosphorylation that takes place in the mitochondria. Another term for ubiquinone is coenzyme Q. Ubiquinone is a vital factor in the cellular respiration of plants. It also helps in the protection of biological membranes against free radicals.

The structure of ubiquinone consists of a ring of ubiquinone (through the metabolism of the amino acid phenylalanine) along with a long chain of carbon called polyprenyl. Researchers believe that by using ubiquinone, artificially engineered and bred plants can be made with more stress-resistant properties and have increased nutritional value properties. Ubiquinone is present in the inner membrane of the mitochondria of the plant cell.

What is Plastoquinone?

Plastoquinone is a type of prenylquinone that acts as an electron carrier in the electron transport chain of light-dependent reaction of photosynthesis. Plastoquinone A (PQ-A) or plastoquinone 09 (PQ-9) is the most common type of plastoquinone present in plants. This type is a 2, 3-dimethyl-1,4-benzoquinone molecule with a side chain of nine isoprenyl units. The other types of plastoquinones present in the plant cell consist of shorter side chains such as PQ-3 and its analogs such as PQ-B, PQ-C, and PQ-D. The oxidation states of plastoquinone are plastosemiquinone (unstable) and plastoquinol. Plastoquinol is a reduced form, which acts as an antioxidant by reducing reactive oxygen species.

The main role of plastoquinone is to act as an electron carrier in light-dependent photosynthesis. It is present in the thylakoid membrane of the chloroplast. During the light reaction of photosynthesis, plastoquinone facilitates the transfer of electrons from PS-II to the Cytb6f complex.

What are the Similarities Between Ubiquinone and Plastoquinone?

• Ubiquinone and plastoquinone are prenylquinones.
• They are present in the plant cell.
• Moreover, they are involved in the electron transport chain.
• Both molecules are electron carriers.
• They both contribute to the growth and development of the plant.

What is the Difference Between Ubiquinone and Plastoquinone?

Ubiquinone is present in the inner membrane of the mitochondria, while plastoquinone is present on the thylakoids of chloroplast. Thus, this is the key difference between ubiquinone and plastoquinone. Moreover, ubiquinone acts as an electron carrier in the electron transport chain of oxidative phosphorylation, while plastoquinone acts as an electron carrier in the electron transport chain of light dependant reactions of photosynthesis. In addition, ubiquinone is light-dependent, while plastoquinone is light-independent.

The below infographic presents the differences between ubiquinone and plastoquinone in tabular form for side-by-side comparison.

Summary – Ubiquinone vs Plastoquinone

Ubiquinone and plastoquinone are two important prenylquinones that function as electron transporters in the electron transport chain of oxygenic photosynthesis and aerobic respiration, respectively. Ubiquinone is present in the inner membrane of the mitochondria. Plastoquinone is present on the thylakoids of chloroplast. Both are prenylquinones. Ubiquinone is a vital factor for the cellular respiration of plants. It also assists in the protection of biological membranes against free radicals. During the light reaction of photosynthesis, plastoquinone facilitates the transfer of electrons from PS-II to Cytb6f complex. So, this summarizes the difference between ubiquinone and plastoquinone.

Reference:

1. Liu, Miaomiao, and Shanfa Lu. “Plastoquinone and Ubiquinone in Plants: Biosynthesis, Physiological Function and Metabolic Engineering.” Frontiers.

Image Courtesy:

1. “Ubiquinone ubiquinol conversion” By Triples in LA – Own work (CC BY 3.0) via Commons Wikimedia
2. “Photosystem II – multilingual” By Kaidor – Own work (CC BY-SA 4.0) via Commons Wikimedia