Photosynthetic reaction centre

A complex of proteins and pigments that performs the primary energy conversion reactions of photosynthesis

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Photosynthetic Reaction Center Drawing

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The photosynthetic reaction centre is a complex of several proteins, pigments, and other co-factors that together execute the primary energy conversion reactions of photosynthesis. These reactions are crucial for the conversion of light energy into chemical energy, which is then used by plants, algae, and some bacteria to fuel their metabolic processes.

Structure

The photosynthetic reaction centre is embedded in the thylakoid membrane of chloroplasts in plants and algae, and in the plasma membrane of photosynthetic bacteria. It consists of several key components:

• Proteins: These form the structural framework of the reaction centre and help in the proper positioning of pigments and other cofactors.
• Pigments: These include chlorophylls and carotenoids, which are responsible for capturing light energy.
• Cofactors: These include quinones, iron-sulfur clusters, and other molecules that participate in electron transfer.

Function

The primary function of the photosynthetic reaction centre is to convert light energy into a stable chemical form. This process involves several steps:

1. Light Absorption: Pigments in the reaction centre absorb photons of light, exciting electrons to a higher energy state. 2. Electron Transfer: The excited electrons are transferred through a series of cofactors, creating a charge separation across the membrane. 3. Energy Conversion: The energy from the charge separation is used to drive the synthesis of adenosine triphosphate (ATP) and nicotinamide adenine dinucleotide phosphate (NADPH), which are essential for the Calvin cycle.

Types of Photosynthetic Reaction Centres

There are two main types of photosynthetic reaction centres, classified based on their electron donor and acceptor molecules:

• Type I Reaction Centres: Found in green sulfur bacteria and heliobacteria, these use iron-sulfur clusters as terminal electron acceptors.
• Type II Reaction Centres: Found in purple bacteria and cyanobacteria, these use quinones as terminal electron acceptors.

Evolution

The evolution of photosynthetic reaction centres is a key event in the history of life on Earth. It is believed that the earliest photosynthetic organisms were anoxygenic, meaning they did not produce oxygen as a byproduct. The development of oxygenic photosynthesis, which uses water as an electron donor and produces oxygen, was a major evolutionary advancement that led to the rise of aerobic life forms.

Applications

Understanding the structure and function of photosynthetic reaction centres has important implications for bioengineering and renewable energy. Researchers are exploring ways to mimic these natural processes to develop efficient solar energy conversion systems.

Gallery

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  First stage sbep2

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  Photosystem II 2AXT

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  PSII new design

Related pages

• Photosynthesis
• Chlorophyll
• Thylakoid
• Electron transport chain
• Calvin cycle