How does photosystem work

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Crystal structure of oxygen-evolving photosystem II from Thermosynechococcus vulcanus at 3. Photosystem II Photosystem II captures the energy from sunlight and uses it to extract electrons from water molecules Photosystem II from cyanobacteria.

The membrane is shown schematically in gray. Three billion years ago, our world changed completely. Before then, life on Earth relied on the limited natural resources found in the local environment, such as the organic molecules made by lightning, hot springs, and other geochemical sources.

However, these resources were rapidly being used up. Everything changed when these tiny cells discovered a way to capture light and use it to power their internal processes. The discovery of photosynthesis opened up vast new possibilities for growth and expansion, and life on the earth boomed. With this new discovery, cells could take carbon dioxide out of the air and combine it with water to create the raw materials and energy needed for growth.

Today, photosynthesis is the foundation of life on Earth, providing with a few exotic exceptions the food and energy that keeps every organism alive. Modern cells capture light using photosystem proteins, such as the one pictured here from PDB entry 1s5l. These photosystems use a collection of highly-colored molecules to capture light. These light-absorbing molecules include green chlorophylls, which are composed of a flat organic molecule surrounding a magnesium ion, and orange carotenoids, which have a long string of carbon-carbon double bonds.

These molecules absorb light and use it to energize electrons. The high-energy electrons are then harnessed to power the cell. Photosystem II is the first link in the chain of photosynthesis. It captures photons and uses the energy to extract electrons from water molecules.

These electrons are used in several ways. First, when the electrons are removed, the water molecule is broken into oxygen gas, which bubbles away, and hydrogen ions, which are used to power ATP synthesis.

David Chandler has been a freelance writer since whose work has appeared in various print and online publications. A former reconnaissance Marine, he is an active hiker, diver, kayaker, sailor and angler. He has traveled extensively and holds a bachelor's degree from the University of South Florida where he was educated in international studies and microbiology.

What Happens in the Light Reaction of Photosynthesis? Two Stages of Photosynthesis. What Are Light Independent Reactions? When studying a photosynthetic organism, scientists can determine the types of pigments present by using a spectrophotometer.

These instruments can differentiate which wavelengths of light a substance can absorb. Spectrophotometers measure transmitted light and compute its absorption. By extracting pigments from leaves and placing these samples into a spectrophotometer, scientists can identify which wavelengths of light an organism can absorb. The overall function of light-dependent reactions, the first stage of photosynthesis, is to convert solar energy into chemical energy in the form of NADPH and ATP, which are used in light-independent reactions and fuel the assembly of sugar molecules.

Light energy is converted into chemical energy in a multiprotein complex called a photosystem. Each photosystem consists of multiple antenna proteins that contain a mixture of — chlorophyll a and b molecules, as well as other pigments like carotenoids.

Pigments in the light-harvesting complex pass light energy to two special chlorophyll a molecules in the reaction center. The light excites an electron from the chlorophyll a pair, which passes to the primary electron acceptor. The excited electron must then be replaced. In a photosystem II, the electron comes from the splitting of water, which releases oxygen as a waste product. In b photosystem I, the electron comes from the chloroplast electron transport chain.

The two photosystems absorb light energy through proteins containing pigments, such as chlorophyll. The light-dependent reactions begin in photosystem II. In PSII, energy from sunlight is used to split water, which releases two electrons, two hydrogen atoms, and one oxygen atom.

When a chlorophyll a molecule within the reaction center of PSII absorbs a photon, the electron in this molecule attains a higher energy level. Because this state of an electron is very unstable, the electron is transferred to another molecule creating a chain of redox reactions called an electron transport chain ETC. Therefore, another photon is absorbed by the PSI antenna.

That energy is transmitted to the PSI reaction center. This process illustrates oxygenic photosynthesis, wherein the first electron donor is water and oxygen is created as a waste product.

The electron transport chain moves protons across the thylakoid membrane into the lumen. At the same time, splitting of water adds protons to the lumen while reduction of NADPH removes protons from the stroma.

The net result is a low pH in the thylakoid lumen and a high pH in the stroma. This process, called photophosphorylation, occurs in two different ways.