Name: photosystem i and nadph formation
Uploaded: 2019-03-11T09:21:12.000Z
Duration: 1 min 27 s
Channel: JoVE

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Photosystem I

בדומה לפוטוסיסטם 2, בפוטוסיסטם 1, פוטונים גם כן נבלעים על-ידי מולקולות פיגמנט בתצמיד איסוף האור, כדי להעביר אנרגיה למרכז התגובה, ובעקבות החמצון, אלקטרון בעל אנרגיה גבוהה עובר אל קולט האלקטרונים הראשי. עם זאת, הפעם, אלקטרונים החסרים מזוג ה‫כלורופילים a מוחלפים באלקטרונים שהועברו מפוטוסיסטם 2 דרך שרשרת מעבר האלקטרונים, מן המולקולה הנשאית פלסטוקינון אל תצמיד הציטוכרום הדו-חלבוני, ואל חלבון אחר, פלסטוציאנין. האנרגיה המשוחררת על-ידי תהליך זה, משמשת להזרמת פרוטונים לתוך חלל התילקואידי דרך תצמיד הציטוכרום, היוצר מפל פרוטונים שמפיק ATP באמצעות כמיאוסמוזה.ברגע שהאלקטרון עובר דרך מרכז תגובה זה, הוא נכנס לשרשרת מעבר האלקטרונים השנייה, החל בתצמיד חלבונים פרדוקסין. מכאן, האלקטרון היחיד נקלט על-ידי NADP רדוקטאז, יחד עם עוד אלקטרון ופרוטון, כדי ליצור לבסוף את תוצר האנרגיה NADPH.

<ol>
	<li>Cardona, T., Shao, S., Nixon, P.J. שיפור פוטוסינתזה בצמחים: תגובות האור. מאמרים בביוכימיה. 62 (1), 85-94 (2018).</li>
</ol>

מערכות אור i

<div style="direction:rtl">למרות שמבחינה מבנית דומה למערכת אור II (PSII), למערכת אור I (PSI) יש ספק אלקטרוני ומקבל אלקטרונים שונה. שתי מערכות האור הללו פועלות במקביל. אלקטרון מעורר מ-PSII מועבר ל-PSI באמצעות שרשרת הובלה של אלקטרונים בקרום התילקואיד של הכלורופלסט, המורכב ממולקולת הנשא פלסטוקינון, קומפלקס ציטוכרום כפול חלבון ופלסטוציאנין. כשהאלקטרונים נעים בין PSII ל-PSI, הם מאבדים אנרגיה וחייבים להפעיל אותם מחדש על ידי PSI. כתוצאה מכך, פוטון נוסף נספג בפיגמנטים של קומפלקס אנטנת PSI ומועבר למרכז התגובה PSI הנקרא P700. P700 מחומצן ושולח אלקטרון בעל אנרגיה גבוהה ל-+^NADP כדי ליצור NADPH. בדיוק כפי ש-PSII לוכד את האנרגיה כדי ליצור גרדיאנטי פרוטונים כדי ליצור ATP, PSI לוכד את האנרגיה כדי להפחית את +^NADP לתוך NADPH. לאחר שהאנרגיה מהשמש הופכת לאנרגיה כימית בצורה של מולקולות ATP ו-NADPH, לתא יש את הדלק הדרוש לבניית מולקולות פחמימות לאגירת אנרגיה לטווח ארוך בפיונית של הכלורופלסט.</div>

מערכות אור I

למרות שהמבנה דומה לפוטוסיסטם II (PSII), לפוטוסיסטם I (PSI) יש ספק אלקטרונים שונה ומקבל אלקטרונים שונה.
שני אלה ...

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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 re-energized by photosystem I.

To do this, the pigments in the photosystem I antenna complex absorb another photon. The energy is passed to the reaction center called P700. P700 then sends a high-energy electron to NADP+ and forms NADPH.

Photosystem II uses light energy to build a proton gradient and make ATP. Photosystem I captures light energy to reduce NADP+ into NADPH. After ATP and NADPH are made, the cell has the energy it needs to build carbohydrate molecules for long-term storage in the stroma of the chloroplast.

Photosystem I and NADPH Formation

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 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...

photosystem i

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 I re-energizes electrons, reduces NADP+ to NADPH, and works with photosystem II to help build sugars in chloroplasts.

Photosystem I and NADPH Formation | JoVE K12

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Photosystem I and NADPH Formation

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