What Are Photosystems?

The functional and structural constituents of photosynthetic protein complexes are called photosystems. They collaborate to perform the basic photochemistry of photosynthesis, which includes light absorption, energy transfer, and electron transport Chloroplast membranes are found in plants and algae, while cytoplasmic membranes are found in photosynthetic bacteria.

• The two types of photosystems are PSI and PSII.

PSII and PSI, respectively, absorb red and far-red light. Although photosynthetic activity may be evaluated when photosystems are exposed to either red or far-red light, photosynthetic activity is at its peak when plants are exposed to both wavelengths of light. Studies have revealed that when the two wavelengths are mixed, they have a synergistic rather than additive effect on photosynthetic activity.

Photosystems

Photosystems are functional units in photosynthesis that are defined by pigment organization and association patterns. In the thylakoid membranes, photosystems are physically present. There are two types of photosystems, as shown in the diagram: photosystem I (PSI) and photosystem II (PSII) (PSII). Although PSII is the first protein to act throughout the photosynthetic light transformation process, it was given that name since it was discovered second.

The antenna complex, which is made up of hundreds of pigment molecules that collect photons and send them to the reaction Centre, which is made up of Chl a molecules in a protein matrix, is the first part of each photosystem. When excitation energy reaches chlorophyll at the reaction Centre, an electron transport chain is initiated. PSI is made up of chlorophyll b, chlorophyll an (a-670, a-680, a-695, a-700), and carotenoids, with one chlorophyll a-700 form (named Chl a-P700) serving as the active reaction Centre on the thylakoid membrane’s outer surface. PSII contains chlorophyll b, chlorophyll a (forms a-660, a-670, a-680, a-695, a-700), phycobilins, and xanthophyll; the active reaction Centre is a Chl a-P680 form.

Photosystem Constituents / made up of

Each photosystem is made up of a core complex and a light-harvesting complex. Each of the core complexes reacts Centre that contains photochemically oxidized P700 or P680 pigments, as well as electron donors and acceptors. As a result, the photosystem has been split in half. Antenna Complex: Antenna Complex is a light-harvesting complex made up of proteins and a variety of chlorophyll a, chlorophyll b, and carotenoids molecules. The reaction Centre is made up of one or more chlorophyll molecules, as well as the electron transport system’s major electron acceptor and related electron carriers.

The majority of the pigments in the photosystem are chlorophyll and accessory pigments. Chlorophyll’s main function is to collect light energy in the form of photons to perform photosynthesis, whereas accessory pigments serve as secondary light-absorbing pigments that help chlorophyll perform better overall. A good example of an accessory pigment is carotenoids. The yellow, red, or purple carotenoid pigments absorb light at a wavelength that is not absorbed by chlorophyll. The most important are beta carotene, a red-orange isoprenoid, and yellow carotene lutein. The photosystem’s essential components are photochemical reaction centres and antenna molecules, collectively known as the light-harvesting complex. Photosynthetic reactions take place in a photochemical reaction system, which is found in chlorophyll. Light energy is converted into electrochemical energy by a particular chlorophyll molecule. The light-harvesting complex’s accessory pigments absorb a photon and deliver it to the reaction system. This is referred to as excitant transfer. These systems interact to form a fully functional photosystem.

What are the molecules in Photosystems?

Light-harvesting pigments such as chlorophyll a, chlorophyll b, and carotenoids can be found in chloroplast thylakoid membranes. As previously established, pigments and proteins are organized into complexes called photosystems. In each photosystem, proteins, 300-400 chlorophylls, and other pigments make up light-harvesting complexes. When a pigment absorbs a photon, one of its electrons is boosted to a higher-energy orbital, becoming excited.

In a photosystem, the majority of pigments behave like an energy funnel, funnelling energy inward to a central reaction centre. When one of these pigments is activated by light, it transmits energy to a nearby pigment via direct electromagnetic interactions, a process known as resonance energy transfer. The neighbour pigment can then transfer energy to one of its neighbours, continuing the cycle indefinitely. The donor molecule cannot require more energy for excitation than the receiver molecule, but it may require less (i.e., it may absorb light of a longer wavelength). 

Conclusion

In the chloroplast, pigment molecules grouped into photosystems capture sunlight. Photosystems are pigment clusters with accompanying molecules such as proton (hydrogen ion) pumps, enzymes, coenzymes, and Cytochromes. Each photosystem comprises around 200 molecules of chlorophyll and approximately 50 molecules of a pigment family known as carotenoids. The energy of sunshine is transformed into chemical energy in the photosystem’s reaction centre. The antenna in the centre is sometimes referred to as a light-harvesting antenna.