Name: photosystem ii and water splitting
Uploaded: 2019-03-11T09:21:12.000Z
Duration: 1 min 22 s
Channel: JoVE

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HS-ESS2-6

Photosystem II

في النظام الضوئي الثاني،وهو مركب متعدد البروتينات،يتم امتصاص الفوتونات ويتم تمرير طاقتها من خلال الجزء الحاصد للضوء من قبل العديد من جزيئات الصِباغ الرابطة مثل الكلوروفيل a و b والكاروتينات. هذا الامتصاص النشط يولد الطاقة التي يتم نقلها لزوج من جزيئات الكلوروفيل المعروفة باسم P680 في مركز التفاعل. هنا جزئي الكلوروفيل يتخصصون في الخضوع للأكسدة حيث يتخلون عن إلكترون نشط إلى الجزيء الأساسي المُستقبِل للإلكترون في عملية تسمى photoact.ثم يتم استبدال الإلكترون المفقود عن طريق تقسيم الماء إلى اثنين من أيونات الهيدروجين وذرة أكسجين واحدة،مُطلقة إلكترونين والتي يتم إرسالها واحدًا تلو الآخر إلى مركز التفاعل. الآن الإلكترونات جاهزة للانتقال من خلال سلسلة نقل الإلكترونات إلى النظام الضوئي الأول. ويمكن أن يتحد الأكسجين مع أكسجين آخر من الماء لتشكيل غاز يصعد إلى الهواء الجوي وتراكم أيونات الهيدروجين داخل الثايلاكويد يخلق تدرج تركيزي حيث تلك الموجودة في منطقة تركيز عالية،تتدفق من خلال قناة بروتين شبه دائمة تدعى سينثاز ATP،إلى منطقة ذات تركيز منخفض في السَدَى.تُعرف هذه العملية باسم التَناضُحٌالكِيمْيائِيّوتنتج طاقة،مما يسمح للسينثاز ATP لإرفاق مجموعة فوسفات ثالثة إلى ADP لتشكيل منتج الطاقة ATP.

<ol>
	<li>ساسي ، شينا ، جيلي فينكاتيش ، راويا فتح الله دانيشي ، ومايانك أناند جوروراني. "البروتينات الخارجية للنظام الضوئي الثاني ودورها المفترض في تحمل الإجهاد اللاأحيائي في النباتات العليا." النباتات 7 ، العدد 4 (ديسمبر 2018): 100.</li>
	<li>ياماموتو ، ياسوسي. "مراقبة جودة النظام الضوئي الثاني: ترتبط آليات تجنب وتحمل ضغوط الضوء والحرارة ارتباطا وثيقا بسيولة غشاء الثايلاكويدات." الحدود في علوم النبات 7 (2016).</li>
</ol>

النظام الضوئي ii

<h4>نظره عامه</h4>

النظام الضوئى II هو مركب متعدد البروتينات مضمن داخل غشاء الثايلاكويد حيث يحصد الطاقة الضوئية. تنقل جزيئات الكلوروفيل الطاقة إلى زوج معين من جزيئات الكلوروفيل a في مركز تفاعل النظام الضوئي II. هنا ، تفقد جزيئات الكلوروفيل a إلكتروناً (أكسدة) ، وتنقله إلى متقبل إلكترون أولي. تمر الإلكترونات المتبرع بها عبر سلسلة نقل الإلكترون إلى النظام الضوئي I. يؤدي تقسيم جزيء الماء إلى إطلاق ذرة أكسجين واحدة وبروتونين (H+)وإلكترونين. تحل الإلكترونات محل الإلكترونات المتبرع بها لجزيئي الكلوروفيل a في مركز التفاعل. تتفاعل ذرة الأكسجين على الفور مع ذرة أكسجين أخرى ، مما ينتج O2 يتم إطلاقه في الغلاف الجوي. تتراكم البروتونات وتخلق تدرج تركيز عبر غشاء الثايلاكويد الذي يحرك تخليق أدينوسين ثلاثي الفوسفات في عملية تسمى التناضح الكيميائي.

<h4>حصاد الضوء في النظام الضوئي (II).</h4>

يحصد مركب النظام الضوئي II متعدد البروتينات الفوتونات وينقل الطاقة من خلال أصباغه المرتبطة بالكلوروفيل a و b والكاروتينات. تتمتع الكاروتينات بوظيفة وقائية لأنها تساعد في تبديد الكمية الهائلة من الطاقة التي يمكن أن تلحق الضرر بأنسجة النبات.

تنتقل الطاقة من جزيء كلوروفيل إلى جزيء كلوروفيل حتى تصل إلى زوج من جزيئات الكلوروفيل a المتخصصة في منطقة تسمى مركز التفاعل. يُعرف مركز التفاعل أيضاً باسم P680 لأنه يمتص الضوء بطول موجة ٦٨٠ نانومتر. الطاقة قوية بما يكفي لكسر إلكترون من جزيء الكلوروفيل (الأكسدة). ينتقل الإلكترون الحر إلى جزيء متقبل إلكترون أولي ، في عملية تسمى تأثير ضوئي. يتم استبدال إلكترون الكلوروفيل a في مركز التفاعل بواحد من إلكترونين يتم إطلاقهما في انقسام جزيء الماء.

<h4>تدرج البروتون و توليد أدينوسين ثلاثي الفوسفات</h4>

يولد انقسام الماء في النظام الضوئي II أيضا ذرة أكسجين تتحد مع ذرة أكسجين ثانية. و O2 الناتج يهرب الى الغلاف الجوي. كما أن التفاعل ينتج اثنين من البروتونات (H+) يتراكمان ويخلقان تدرج تركيز لتشغيل قناة بروتينية متخصصة شبه منفذة تسمى سينثيز أدينوسين ثلاثي الفوسفات. تسمى عملية انتقال البروتونات من تركيز عالٍ في الثايلاكويد ، عبر القناة إلى منطقة تركيز أقل في السدى ، بالتناضح الكيميائي. يخلق التناضح الكيميائي طاقة تسمح لـ سينثيز أدينوسين ثلاثي الفوسفات بربط مجموعة فوسفات ثالثة بأدينوسين ثنائي الفوسفات لتشكيل جزيء الطاقة أدينوسين ثلاثي الفوسفات.

النظام الضوئي II

يحصد النظام الضوئي المركب متعدد البروتينات II (PS II) الفوتونات وينقل طاقتها من خلال أصباغه المرتبطة إلى مركز تفاعله ، و ...

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photosystem ii and water splitting

Photosystem II is a multi-protein complex that captures light energy and begins the flow of electrons in photosynthesis. It uses bound pigments to harvest photons and send that energy to its reaction center. From there, the energy continues through the electron transport chain and on to photosystem I.

The pigments in photosystem II include chlorophyll a, chlorophyll b, and carotenoids. They are arranged in two parts of the photosystem: the antenna complex and the reaction center. The antenna complex absorbs light and funnels that energy to the special chlorophyll pair in the reaction center.

Carotenoids also have a protective role. They help dissipate excess absorbed energy and reduce damage to plant tissue. In the reaction center, also called P680, a photon excites an electron in chlorophyll. The high-energy electron is released and passed to the primary electron acceptor.

P680 then replaces the lost electron by taking low-energy electrons from water splitting. Splitting one H2O molecule releases two electrons, two hydrogen atoms, and one oxygen atom. Two oxygen atoms from two H2O molecules join to form oxygen gas, which is released into the environment. The hydrogen ions also help build the proton gradient across the thylakoid membrane. That gradient is essential for ATP synthesis in the chloroplast.

Photosystem II and Water Splitting

what is photosynthesis?

Photosynthesis in Chloroplasts and Leaves

Photosynthesis happens in plants and in some bacteria. It is the process that captures carbon dioxide and solar energy to make glucose. Glucose stores chemical energy as carbohydrates. The overall biochemical equation is 6 CO2 + 6 H2O + light energy → C6H12O6 + 6 O2. Photosynthesis also releases oxygen into the atmosphere and helps maintain Earth’s atmospheric oxygen content. Photosynthetic reactions take place in chloroplasts, which are specialized membrane-enclosed parts of the plant cell.

light as energy

How Plant Pigments Capture Light

Photosynthesis uses light energy from the sun, which is a form of electromagnetic radiation. The full range of possible wavelengths is called the electromagnetic spectrum. Light is made of photons, which are small packets of energy. Photons act like waves and are described by frequency, wavelength, and amplitude. Waves with higher frequencies carry more energy and have shorter wavelengths. Waves with lower frequencies carry less energy and have longer wavelengths. For most organisms,...

anatomy of chloroplasts

Chloroplasts and Photosynthesis in Plant Cells

Chloroplasts are the organelles where photosynthesis takes place in green algae and plants. They are also found in green stems and unripe fruit. In plants, mesophyll cells in the leaf contain the highest density of chloroplasts. Each chloroplast has a double membrane. The outer membrane faces the plant cell cytoplasm on one side and the chloroplast intermembrane space on the other. The inner membrane separates that narrow space from the stroma, which is the watery interior of the chloroplast.

photosystem ii

Photosystem II is a multi-protein complex that captures light energy and begins the flow of electrons in photosynthesis. It uses bound pigments to harvest photons and send that energy to its reaction center. From there, the energy continues through the electron transport chain and on to photosystem I. The pigments in photosystem II include chlorophyll a, chlorophyll b, and carotenoids. They are arranged in two parts of the photosystem: the antenna complex and the reaction center. The antenna...

photosystem i

Photosystem I and NADPH Formation

Photosystem I helps convert light energy into NADPH during photosynthesis. It works with photosystem II in the thylakoid membrane of the chloroplast, but it uses a different electron supplier and a different electron acceptor. Electrons excited in photosystem II move to photosystem I through an electron transport chain. That chain includes plastoquinone, the dual-protein cytochrome complex, and plastocyanin. As the electrons travel between the two photosystems, they lose energy and must be...

the calvin cycle

Carbon Fixation in Photosynthesis

Photosynthesis uses light energy to turn carbon dioxide into carbohydrates. It also releases oxygen as a by-product. These products help support most food webs and make aerobic life possible. Photosynthesis has two main stages, and they happen in different parts of the chloroplast. The light-dependent reactions take place in the thylakoid membranes. Chlorophyll absorbs light energy there and helps split water molecules. This releases O2 and makes ATP and NADPH. The light-independent reactions...

c4 pathway and cam

Plant Carbon Fixation in Hot Climates

Plant carbon fixation in hot climates can follow the C4 pathway or the CAM pathway. These alternative pathways help some plants reduce energy loss from photorespiration. Photorespiration happens when oxygen levels are high and rubisco, the enzyme in the Calvin cycle, binds O2 instead of CO2. When that happens, photosynthesis slows and energy is used up. The C4 pathway is used by plants such as corn and sugarcane. In mesophyll cells, CO2 first joins with PEP, or phosphoenolpyruvate, through the...

key terms and concepts

Learn how photosystem II captures light, excites P680, splits water, releases oxygen, and helps build the proton gradient needed for ATP synthesis.

Photosystem II and Water Splitting | JoVE K12

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Photosystem II and Water Splitting

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