What is the Difference Between Antenna Complex and Reaction Center

The key difference between antenna complex and reaction center is that antenna complex is an array of proteins and chlorophyll b molecules that transfers light energy to the reaction center of a photosystem, while the reaction center is a complex of several proteins, pigments, and co-factors that executes the primary energy conversion reaction of the photosynthesis process.

Photosynthesis is the process in which plants use sunlight, water, and carbon dioxide to produce oxygen and energy in the form of glucose. The antenna complex and reaction center are two complexes helping the photosynthesis reaction in plants and cyanobacteria. The reaction center is the core complex of the photosystem, and the antenna complex is present around it. Therefore, the antenna complex and reaction center are the two main parts of the photosystem that regulate photosynthesis.

CONTENTS

1. Overview and Key Difference
2. What is Antenna Complex  
3. What is Reaction Center
4. Similarities – Antenna Complex and Reaction Center
5. Antenna Complex vs Reaction Center in Tabular Form
6. Summary – Antenna Complex vs Reaction Center

What is Antenna Complex?

The antenna complex is an array of proteins and chlorophyll b molecules located in the thylakoid membrane of plants, algae, and cyanobacteria, which transfers light energy to the reaction center of a photosystem. Also, the antenna complex mainly consists of chlorophyll b, xanthophylls, and carotenes. Carotenoids have another important function. As they are antioxidants, they prevent photo-oxidative damage of chlorophyll molecules. Each antenna complex normally has between 250 and 400 pigment molecules. The energy these pigments absorb is shuttled by resonance energy transfer to a chlorophyll protein complex called the reaction center of each photosystem. Later, the reaction center initiates a complex series of biochemical reactions.

There are two antenna complexes (LH1 and LH2). Antenna complex I is permanently bound to photosystem I via the plant-specific subunit PSaG. The antenna complex II is normally bound to photosystem II. However, it can undock and bind photosystem II instead of depending on light conditions.

What is Reaction Center?

The reaction center is a complex of several proteins, pigments, and co-factors that executes the primary energy conversion reaction of photosynthesis. The molecular excitation that originates directly either from the sunlight or transferred excitation energy through the antenna complex gives rise to electron transfer reactions along the path of a series of protein-coupled co-factors in the reaction center. These co-factors are normally light-absorbing molecules like chlorophyll, pheophytin, and quinines. A series of biochemical reactions take place in the reaction center.

Firstly, the energy of the photons is used by a pigment to excite its electron. Secondly, the free energy created is then used (via a chain of nearby electron acceptors) to transfer hydrogen atoms from water or H₂S towards CO₂ in order to produce glucose. Ultimately, these electron transfer steps result in the conversion of the energy of photons to stored chemical energy in glucose.

What are the Similarities Between Antenna Complex and Reaction Center?

• The antenna complex and reaction center are the two main parts of a photosystem.
• Both complexes are present in the thylakoid membrane.
• Both complexes can be identified in plants, algae, and cyanobacteria.
• The antenna complex is bound to the reaction center through a specific subunit.
• Both complexes are very important in regulating photosynthesis.

What is the Difference Between Antenna Complex and Reaction Center?

Antenna complex is an array of proteins and chlorophyll b molecules that transfers light energy to the reaction center of a photosystem, while the reaction center is a complex of several proteins, pigments, and co-factors that execute the primary energy conversion reaction of photosynthesis. Thus, this is the key difference between antenna complex and reaction center. Furthermore, the antenna complex has chlorophyll b molecules while the reaction center has chlorophyll a molecules.

The below infographic presents the differences between antenna complex and reaction center in tabular form for side-by-side comparison.

Summary – Antenna Complex vs Reaction Center

The antenna complex and reaction center are the two main parts of the photosystem that regulate the photosynthesis process. Antenna complex is an array of proteins and chlorophyll b molecules. It transfers light energy to the reaction center. The reaction center is a complex of several proteins, pigments, and co-factors. It executes the primary energy conversion reaction of photosynthesis. So, this is the summary of the difference between antenna complex and reaction center.

Reference:

1. “Antenna Pigment.” An Overview | ScienceDirect Topics.
2. “Photosynthetic Reaction Centre.” An Overview | ScienceDirect Topics.

Image Courtesy:

1. “FMO Complex Simple Diagram” By OMM93 – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Thylakoid membrane 3” By Somepics – Own work (CC BY-SA 4.0) via Commons Wikimedia