The Z-scheme or non-cyclic photosynthetic processes explain the electron transport system from photosystem-I to photosystem II via the electron shuttles.
In the Z-scheme or non-cyclic photosynthetic processes, the electron transport system describes the movement of electrons from photosystem I (PSI) to photosystem II (PSII) through a series of electron shuttles.
Initially, in PSII, light energy is absorbed by chlorophyll pigments, exciting electrons within the reaction center. These energized electrons are then captured by the primary electron acceptor molecule of PSII, leaving the reaction center positively charged. To replenish the lost electrons, water molecules are split, releasing oxygen gas, protons (H+ ions), and new electrons.
The energized electrons are passed down a series of electron carriers or shuttles, including plastoquinone and plastocyanin, to reach PSI. Plastoquinone accepts the electrons from PSII and transports them to the cytochrome b6f complex. Along this electron transport chain, protons are pumped across the thylakoid membrane and create a proton gradient, which is crucial for ATP synthesis later on.
After reaching the cytochrome b6f complex, the electrons are transferred to plastocyanin, which carries them to PSI. At PSI, another reaction center absorbs light energy, exciting electrons and generating new electron vacancies. The electrons from plastocyanin are then transferred to the primary electron acceptor of PSI.
To complete the non-cyclic process and maintain electron flow, the electrons from PSI are replenished by the oxidation of electron carriers, such as ferredoxin and NADPH. The electrons are eventually used to reduce NADP+ to NADPH, which is an electron carrier that plays a crucial role in the Calvin cycle, where carbon fixation occurs.
Overall, the Z-scheme or non-cyclic photosynthetic processes describe the flow of electrons from water to NADPH, driven by light energy, through a series of electron shuttles. This process generates ATP and NADPH, essential for the production of carbohydrates during the Calvin cycle.
The Z-scheme, also known as the non-cyclic photosynthetic process, describes the movement of electrons in the electron transport system (ETS) during photosynthesis. Specifically, it explains how electrons are transferred from photosystem II (PSII) to photosystem I (PSI) through electron shuttles.
Here's a step-by-step explanation of the Z-scheme:
1. Light energy is absorbed by the pigments within the chloroplasts, primarily in PSII. This energy excites electrons in PSII's reaction center chlorophyll, resulting in electron transfer within PSII.
2. The excited electrons are then passed through a series of electron carriers, including plastoquinone (PQ) and cytochrome b6f complex (Cyt b6f). These carriers are embedded within the thylakoid membrane of the chloroplast.
3. As the electrons are transferred from one carrier to another, energy is released and used to pump protons (H+) across the thylakoid membrane from the stroma to the thylakoid lumen. This creates an electrochemical gradient.
4. The excited electrons eventually reach PSI, where they replace the electrons that were lost from its reaction center chlorophyll. PSI's electrons were initially transferred to an electron acceptor called Ferredoxin (Fd).
5. The electrons transferred to PSI reduce NADP+ (Nicotinamide adenine dinucleotide phosphate) to NADPH, which is an energy-rich molecule used in subsequent stages of photosynthesis.
6. The electrons lost by PSII are replenished by a process called photolysis or water splitting. Water molecules are split into oxygen (O2), protons (H+), and electrons. The electrons are then used to replace those lost by PSII.
Overall, the Z-scheme explains how the excitation of electrons by light energy in PSII leads to the generation of a transmembrane proton gradient and the production of NADPH in PSI. This process is crucial for the synthesis of ATP, the generation of reducing power, and the production of oxygen during photosynthesis.