Name: light-harvesting antennas in reaction centers
Uploaded: 2023-04-30T09:17:03.000Z
Duration: 1 min 29 s
Channel: JoVE

K12 Standards

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NC K-12 Science Standard Course of Study

9-12

Biology

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From Molecules to Organisms- Structures and Processes

LS.Bio.3.2

The Photochemical Reaction Center

A photochemical reaction center is a pigment-protein complex located at the core of each photosystem.
The reaction centers are grouped into two categories depending on their terminal electron acceptors.
Type I reaction center has a ferredoxin and type II has a plastoquinone molecule as the terminal electron acceptor.
Each reaction center also has a special pair of chlorophyll a molecules that absorb specific wavelengths of light.
The PSI reaction center absorbs photons with a wavelength of 700 nanometers and is, therefore, called P700.
In contrast, the PSII reaction center absorbs a wavelength of 680 nanometers and is called P680.
Despite their differences, both PSI and PSII work on a very similar principle.
When the chlorophyll pair in a reaction center absorbs a photon, one of its ground state electrons attains an excited energy level.
Consequently, the chlorophyll molecule becomes excited and must lose the excess energy it possesses for stability. Thus, it emits the energized electron to a nearby electron acceptor.
The positively charged chlorophyll ion pair then withdraws electrons from a donor, like a water molecule, to return to its original state.

the photochemical reaction center

Reaction centers are pigment-protein complexes that initiate energy conversion from photons to chemical entities. Therefore, photochemical reaction center is a more appropriate term that describes these complexes. The Nobel laureates Robert Emerson and William Arnold provided the first experimental evidence of photochemical reaction centers by demonstrating the participation of nearly 2,500 chlorophyll molecules for the release of just one molecule of oxygen. Despite thousands of photosynthetic pigments present within a photosynthetic unit, only a few have photochemical activity. The reaction centers contain fewer pigment molecules that cannot lead to efficient photosynthesis. Therefore, an antenna complex, having a large number and variety of pigments, accumulates significant quantities of photons and transmits their energy to the reaction center. The photochemically active pigments of the reaction center then convert light energy into high-energy electrons that are utilized for downstream chemical reactions.
In oxygen liberating organisms such as cyanobacteria, green and red algae, and higher plants, the reaction center is found inside both photosystems I and II. It is also present in bacteria with a single photosystem. The reaction center of the bacterium- Rhodopseudomonas viridis is the first integral membrane-bound protein to be isolated and studied. The molecular architecture of the R. viridis reaction center resembles the PSII reaction center but lacks an oxygen-evolving complex and, therefore, the ability to produce oxygen. It comprises four protein subunits, called H, L, M, cytochrome, and 14 cofactors that include bacterial chlorophyll and carotenoids. The L and M subunits harbor two bacterial chlorophyll molecules that absorb a photon of 870nm wavelength, thus the name P870 reaction center. The R. viridis reaction center also comprises a bacterial pheophytin that acts as the primary electron acceptor, a mobile quinone as the terminal electron acceptor, a membrane-bound cytochromes bc1, and a periplasmic cytochrome bc2. Together, these form an integral component of the light-driven electron transfer cycle in R. viridis.

Reaction centers are pigment-protein complexes that initiate energy conversion from photons to chemical entities. Therefore, photochemical reaction center ...

Education

JoVE Core

Cell Biology

Unit 1

Chloroplasts and Photosynthesis

KEY TERMS AND CONCEPTS

light-harvesting antennas in reaction centers

Light-harvesting antennas and reaction centers work together in photosynthesis. A reaction center is a pigment-protein complex that starts the conversion of light energy into chemical energy. The term photochemical reaction center is more precise because these complexes carry out the first light-driven chemical step.

Robert Emerson and William Arnold gave the first experimental evidence for these centers. They showed that nearly 2,500 chlorophyll molecules were involved in the release of just one oxygen molecule. That result showed that only a few pigments in a photosynthetic unit are actually photochemically active.

Most pigments in a photosynthetic unit belong to the antenna complex. This complex contains many different pigments and collects large amounts of photons. It then transfers that energy to the reaction center, where the active pigments turn light energy into high-energy electrons for later chemical reactions.

In oxygen-releasing organisms, such as cyanobacteria, green and red algae, and higher plants, reaction centers are found in both photosystems I and II. They also occur in bacteria that have only one photosystem. A well-known example is the reaction center of Rhodopseudomonas viridis, the first integral membrane-bound protein to be isolated and studied.

The R. viridis reaction center has a structure that resembles the PSII reaction center, but it does not have an oxygen-evolving complex. As a result, it cannot produce oxygen. It contains four protein subunits, called H, L, M, and cytochrome, along with 14 cofactors that include bacterial chlorophyll and carotenoids.

The L and M subunits hold two bacterial chlorophyll molecules that absorb light at 870 nm, so this complex is called the P870 reaction center. It also includes bacterial pheophytin, which acts as the primary electron acceptor, and a mobile quinone, which serves as the terminal electron acceptor. A membrane-bound cytochrome bc1 and a periplasmic cytochrome bc2 help complete the light-driven electron transfer cycle in R. viridis.

Light-Harvesting Antennas in Reaction Centers

light-harvesting-antennas-in-reaction-centers

what is photosynthesis?

Photosynthesis Powers the Food Chain

Photosynthesis powers the food chain by turning sunlight into usable chemical energy. It is the only biological process that can capture energy from sunlight and convert it into chemical energy that organisms use to support metabolism. Photosynthesis also provides the oxygen needed by many living things. Organisms are often grouped by how they get food. Autotrophs are organisms that make their own food. Plants, algae, and cyanobacteria are autotrophs, and because they use light to make...

the anatomy of chloroplasts

How Chloroplasts Power Photosynthesis

Chloroplasts are the organelles that power photosynthesis in green algae and plants. They are found in green stems and unripe fruit as well as in leaves. Inside chloroplasts, the two stages of photosynthesis work together to turn sunlight, carbon dioxide, and water into chemical energy. The light-dependent reactions capture sunlight and release oxygen. They also make ATP and NADPH, which are energy-rich molecules. The light-independent reactions then use ATP and NADPH to capture CO2 and build...

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Photorespiration, C4, and CAM Pathways

Photorespiration and the C4 and CAM pathways change how plants handle carbon dioxide during photosynthesis. These processes matter because RuBisCo, the enzyme that starts carbon dioxide fixation, works very slowly. A typical enzyme can process about a thousand molecules per second, but RuBisCo fixes only around three carbon dioxides per second. To make up for this slow rate, photosynthetic cells produce very large amounts of RuBisCo. That is why it is the most abundant single enzyme on Earth. <br...

Light-harvesting antennas and reaction centers work together in photosynthesis. A reaction center is a pigment-protein complex that starts the conversion of light energy into chemical energy. The term photochemical reaction center is more precise because these complexes carry out the first light-driven chemical step. Robert Emerson and William Arnold gave the first experimental evidence for these centers. They showed that nearly 2,500 chlorophyll molecules were involved in the release of just...

the antenna complex

Light-Harvesting in Photosynthesis

Light-harvesting in photosynthesis depends on the antenna complex, also called the light-harvesting complex (LHC). Plants and other photosynthetic organisms use this system to collect direct sunlight with pigments in both the reaction center and the antenna complex. The reaction center is the main site of photochemical reactions. Under average light conditions, the reaction center pigments absorb light more slowly than the electron transport chain can use it. The reaction center alone cannot...

photosystems

Photosystems in Light Reactions

Photosystems are pigment-rich protein complexes that help drive the light reactions of photosynthesis in plants, algae, and cyanobacteria. They are embedded in the thylakoid membrane inside the chloroplast. Their job is to capture light energy and pass it along for chemical use. Each photosystem contains many pigment molecules, including chlorophylls and carotenoids. These pigments are arranged in two parts: the antenna complex and the reaction center. The antenna complex absorbs photons and...

the z-scheme of electron transport in photosynthesis

the-z-scheme-of-electron-transport-in-photosynthesis

How Electron Flow Powers the Z-Scheme

The Z-scheme explains how electrons move through the light reactions of photosynthesis. In this process, light energy drives electrons from water to NADP+, and oxygen is released when water splits. Because water is hard to oxidize, the reaction needs a strong oxidizing agent. That role is filled by oxidized P680, also called P680+. It is the first product of the light reactions and is known as the most powerful oxidizing agent in biology. After it gains an electron from water-splitting, P680+...

key terms and concepts

Learn how antenna complexes deliver light to reaction centers and how the R. viridis P870 system passes electrons through photosynthesis-related pathways.

Light-Harvesting Antennas in Reaction Centers | JoVE K12

cell biology

JoVE Core Cell Biology illustrates complex cellular processes in easy-to-understand yet comprehensive animated video lessons. This collection focuses on the essential components and functions of cells, including organelles and membranes, cellular transport, and cell energetics. It is complemented by scientist-in-action videos that demonstrate the application of cell biology in real-world research experiments.

Pennsylvania State Academic Standards

Life Science

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Matter and Energy in Organisms and Ecosystems

3.1.9-12.E

3.1.9-12.J

3.1.9-12.K

Louisiana Student Standards for Science

High School

Life Sciences

From Molecules To Organisms: Structures And Processes

HS-LS1-5

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Ecosystems: Interactions, Energy And Dynamics

HS-LS2-1

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Ohio’s Learning Standards and Model Curriculum

Cells

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BIO.2

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Minnesota Academic Standards in Science

3.1.1 9L.3.1.1.2

3.2.1 9L.3.2.1.3

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New Jersey Student Learning Standards for Science

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HS.L2U1.21

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HS+B.L2U1.8

Alabama Course of Study Science

9-12.B.1.5.b

Florida Department of Education

SC.912.L.18

SC.912.L.18.7

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South Carolina College and Career Ready Science Standards

B-LS1-5

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Botany

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Photosynthesis

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Light-Harvesting Antennas in Reaction Centers

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