#photosystem

[tenth-sentence]

The reaction centres are called photosystem I (PS I) and photosystem II (PS II) (figure 12.3).

"Chemistry" 2e - Blackman, A., Bottle, S., Schmid, S., Mocerino, M., Wille, U.

[whats-in-a-sentence]

These properties of the two photosystems are shown schematically in Figure 7.13. The scheme of photosynthesis depicted in Figure 7.13, called the Z (for zigzag) scheme, has become the basis for understanding O2-evolving (oxygenic) photosynthetic organisms.

"Plant Physiology and Development" int'l 6e - Taiz, L., Zeiger, E., Møller, I.M., Murphy, A.

[tenth-sentence]

The PSI reaction center and it's associated antenna pigments and electron transfer proteins, as well as the ATP synthase enzyme that catalyzes the formation of ATP, are found almost exclusively in the stroma lamellae and at the edges of the grana lamellae.

"Plant Physiology and Development" int'l 6e - Taiz, L., Zeiger, E., Møller, I.M., Murphy, A.

[a-circle-is-round]

[freehealthteacher]

Photosystem II, poised for O2 formation Summary The vast majority of oxygen in Earth's atmosphere is generated by photosynthetic light reactions. This process also plays an integral role in producing energy for Earth's biosphere.

[under-your-ribs]

one, two, my heart { 1/2 }

“Our babies,” Sehun sighs and he feels like he can’t breathe. He wants them, he wants this with Jongin. He wants tomorrow with Jongin, the next day, the next year, the next ten years, for as long as they’re both alive. 

EXO

Pairing: Sehun/Kai

Links: Part  1 | 2 

Author: photosystem

Rating: R

Genre: Romance

Chaptered

Themes & Warnings: Surrogacy, brief mention of miscarriage (half a sentence long), homophobia, kids, marriage. future fic, canon divergence. 

Summary: Future canon. From simplicity to complexity, from Sehun and Jongin, to Sehun and Jongin, from the seconds of nothing to the years of everything, this is how Sehun’s life will play out from now on. (Baby fic)

[themightymitochondria]

Light Dependent Reactions of Photosynthesis

So, first of all a photon of light hits a chlorophyll that is embedded within Photosystem II in the Thylakoid Membrane of a Chloroplast

(Please excuse my awful drawings, I try)

This excites electrons in a chlorophyll to a higher energy level. The photosystem is oxidized (Remember OILRIG: Oxidation is loss, reduction is gain...of electrons).The charge separation between the electrons and PSII also drives the photolysis of water over at the Oxygen Evolving Complex, but as water is a very stable molecule it takes 4 photons to split it! The word equation for this reaction looks like this...

                                              (photolysis)                                    2(H2O)          ---->       O2 + 4H+ + 4e-

What happens to the products of photolysis? Well, Oxygen at this stage is a biproduct as we don't need it and so it simply out of the chloroplast, out of the cell (if not used for respiration) and eventually out of the plant completely and into the air. The protons (H+) however, build up in the Thylakoid Lumen and contributes to a proton gradient. Whereas the electrons are used to reduce the chlorophyll and replace the excited electrons so that the photosystem is ready for another photon to oxidize it again and so the cycles continues.

An electron acceptor is reduced as it accepts the excited electron from Photosystem II

The Electron Acceptor is re-oxidized as it enters The Electron Transport Chain (a chain of proteins in the Thylakoid Membrane ...shock horror) and a series of REDOX reactions occurs. As the electrons move down the ETC energy is released which is used to pump protons from the stroma and into the lumen (protons from the photolysis of water remain in the lumen) creating a high concentration of protons in the Thylakoid Lumen.

  Photophosphorylation The high concentration of protons in the Thylakoid Lumen causes the H+ to move down a concentration gradient through the Thylakoid Membrane via ATPsynthase. This provides the energy for the photophosphorylation of ADP into ATP. The yield of ATP is not as high as Oxidative Phosphorylation during Respiration.

Note: Pi = Inorganic Phosphate.

Anyway! Back to the electrons

Once the electrons have completed the series of REDOX reactions they replace an electron (that has been excited to a higher energy level by a photon) in Photosystem I. The rest is alot similar to what went on in Photosystem II

The excited electron then reduces another Electron Acceptor

The electron acceptor is then oxidized as the electrons are passed onto another Electron Transport Chain

This time, instead of being passed onto another Photosystem, the electrons recombine with protons in the stroma to reduce NADP to form NADPH - the reducing power for the Light Independent Reactions

The whole point of the Light Dependent Reactions is to produce NADPH which are the reducing agents for The Calvin Cycle

[themightymitochondria]

Photosystems in Photosynthesis

Before we kick off this whole Photosynthesis thing we just need to clarify what exactly this mess is

This bad boy isn't as complicated as he looks, he's a Photosystem (Photsystem II to be exact) and basically it's just a collection or pigments and proteins arranged in a certain way. The green stringy things you see in this diagram are chlorophyll.

In the Light Dependent reactions of Photosynthesis there are two of these photosystemy things involved - Photosystem II and Photosystem I (imaginative names), both of which are located in the Thylakoid Membrane of a chloroplast

.

Photosystem II also contains what is known as the Oxygen Evolving Complex which does just what it says on the tin - produces Oxygen, Protons & and Electrons from the photolysis of water molecules.