FOTOSINTESIS Fotosintesis Tempat fotosintesis berlangsung Fotosintesis terjadi di

FOTOSINTESIS

Fotosintesis

Tempat fotosintesis berlangsung ? • Fotosintesis terjadi di kloroplas • Dalam kloroplas terdapat pigmen disebut klorofil. Klorofil berperan penting dalam mengubah energi cahaya menjadi energi kimia Leaf cross section Vein Mesophyll Stomata CO 2 Di bagian daun terdapat bagian yang disebut mesofil. Dalam mesofil terdapat jaringan palisade yang kaya akan kloroplas. Jaringan berklorofil misal daun pada tanaman merupakan tempat utama terjadinya fotosintesis.

Daun – struktur kloroplas

Struktur kloroplas Mesophyll • Tilakoid adalah sistem membran dalam kloroplas (tempat terjadinya reaksi terang). Memisahkan kloroplas menjadi ruang tilakoid dan stroma • Grana kumpulan tilakoid dalam kloroplas • Stroma: daerah cair antara tilakoid dan membran dalam tempat terjadi siklus Calvin Chloroplast 5 µm Outer membrane Thylakoid Stroma Granum Intermembrane space Thylakoid space Inner membrane 1 µm

Persamaan Fotosintesis

Fotosintesis terdiri dari dua proses yaitu -Reaksi terang -Reaksi reduksi karbon (Siklus Calvin) Reduksi CO 2 menjadi karbohidrat melalui oksidasi carrier energi (ATP, NADPH) Reaksi terang memberi energi pada carrier Reaksi reduksi karbon (siklus Calvin) menghasilkan PGAL (phosphoglyceraldehyde)

Fotosintesis ns • Siklus Calvin: reduksi CO 2 menjadi CH 2 O ro • Reaksi terang: mengubah energi cahaya menjadi energi selular Light reactions ct • Melibatkan 2 lintasan metabolik Chloroplast NADP +P Ru. BP Calvin cycle 3 -PGA Ele • Proses dimana organisme yang memiliki kloroplas mengubah energi cahaya menjadi energi kimia Light G 3 P Cellular respiration Cellulosse Starch Other organic compounds

Reaksi Terang • Energi cahaya akan diubah menjadi energi kimia dengan menghasilkan oksigen sebagai produk samping. • Terjadi di dalam membran tilakoid. • Energi cahaya yang diserap klorofil dalam membran tilakoid akan digunakan untuk membentuk ATP dari ADP dan fosfat. • Pada fase ini terjadi fotolisis air yang menghasilkan oksigen.

Cahaya Photosynthetically active radiation (PAR).

The role of light Light provides the energy to: • transfer electrons from water to nicotinamide adenine dinucleotide phosphate NADP+) forming NADPH; • Generate ATP

Pigmen -Substansi yang menyerap cahaya tampak -Menyerap kebanyakan panjang gelombang tetapi paling sedikit menyerap panjang gelombang hijau Pigmen Klorofil a Klorofil b Karotenoid Karotene Xantofil

Klorofil a • Klorofil a adalah pigmen yang secara langsung berpartisipasi dalam reaksi terang • Pigmen lain menambahkan energi ke klorofil a • Penyerapan cahaya meningkatkan elektron ke orbital energi yang lebih tinggi

Fotosistem • Fotosistem merupakan unit pengumpul cahaya dari membran tilakoid. • Setiap fotosistem berupa kompleks dari protein dan jenis molekul lainnya, termasuk antena yang terdiri dari beberapa ratus molekul pigmen. • Pada pusat reaksi energi ini menggerakkan reaksi reduksi-oksidasi. • Elektron tereksitasi dari klorofil pusat reaksi dan ditangkap oleh molekul khusus yang disebut akseptor elektron primer.

Fotosistem • Kumpulan pigmen dan protein yang berasosiasi dengan membran tilakoid yang memanen energi dari elektron yang tereksitasi • Energi yang ditangkap ditransfer antara molekul fotosistem sampai mencapai molekul klorofil pada pusat reaksi

• Pada pusat reaksi terdapat 2 molekul – Klorofil a – Akseptor elektron primer • Pusat reaksi klorofil dioksidasi dengan hilangnya elektron melalui reduksi akseptor elektron primer • Membran tilakoid Terdapat fotosistem I dan II

Klorofil tereksitasi oleh cahaya Saat pigmen menyerap cahaya – Klorofil tereksitasi dan menjadi tidak stabil Primary acceptor Energy of election e– Excited state Heat Photon (fluorescence) Photon Chlorophyll molecule Ground state

Fotofosforilasi Nonsiklik § Reaksi fotofosforilasi nonsiklik adalah reaksi dua tahap yang melibatkan dua yaitu fotosistem I dan II. § Menghasilkan NADPH, ATP, dan oksigen

Non-cyclic photophosphorilation 1. Light energy is absorbed by antenna pigments of PS II. Energy then transferred to the reaction centre of pigment P 680 in PS II. 2. The P 680 becomes photoactivated and high energy (“exited”) electron is released to the primary electron acceptor 3. The electron released is replaced by splitting water into its component. This process is called photolysis

4. The electron is then transferred through plastoquinone, cytochrome complex, plastocyanin & PS I. As electron passed along ETC, they lose energy. The energy released is used to produced ATP 5. High energy electron in P 700 (PS I) is ejected, passes onto electron acceptor then to ferredoxin & NADP+ reductase 6. NADP+ reductase donates the electron to a molecule of NADP+ and stabilizes it by adding a proton to form NADPH is then released into the stroma.

Non cyclic photophosporylation Light energy is absorbed by antenna pigments of PS II. Energy then transferred to the reaction centre of pigment P 680 in PS II.

The P 680 becomes photoactivated and high energy (“exited”) electron is released to the primary electron acceptor The electron released is replaced by splitting water into its component. This process is called photolysis

Water photolysis Photolysis is a process of splitting water molecules using light energy with the release of electrons and photons and oxygen. The photon (H+) are used to reduced NADP+. Oxygen is given off or used in respiration. 2 H 2 O 4 H+ + O 2 + 4 e- The important of photolysis = To replace electron in photosystem II (non-cyclic photophosphorylation) H+ ions reduce NADP+ to NADPH, which is an electron carrier

The electron is then transferred through plastoquinone, cytochrome complex, plastocyanin & PS I. As electron passed along ETC, they lose energy. The energy released is used to produced ATP

High energy electron in P 700 (PS I) is ejected, passes onto electron acceptor then to ferredoxin & NADP+ reductase

NADP+ reductase donates the electron to a molecule of NADP+ and stabilizes it by adding a proton to form NADPH is then released into the stroma.

Aliran elektron siklik – Hanya fotosistem I yang digunakan – Pergerakan elektron dimulai dari fotosistem I dan berakhir di fotosistem I. – Hanya ATP yang dihasilkan Diah Rachmawati-2011

Aliran elektron Terdapat dua rute jalur elektron yang tersimpan pada akseptor elektron primer Dimulai dengan penangkapan energi foton Menggunakan rantai transport elektron dengan sitokrom untuk kemiosmosis Aliran elektron nonsiklik Menggunakan fotosistem II dan I Elektron dari fotosistem II dihilangkan diganti oleh elektron yang didonasikan oleh air Mensintesis ATP dan NADPH Donasi elektron mengkonversi air → O 2 dan 2 H+ Aliran elektron siklik Hanya menggunakan fotosistem I Elektron dari fotosistem I di-recycle Mensintesis ATP

Non cyclic photophosporylation Photosystem I & photosystem II are involved. Cyclic photophosporylation Only Photosystem I is involved Electron flow is non-cyclic Electron flow is cyclic Water is the first electron donor Electron come from photosystem I (P 700) Last electron acceptor is NADP+ Last electron acceptor is photosystem I Products are ATP, NADPH and O 2 ATP is produced 30

Reaksi terang dan kemiosmosis: H 2 O CO 2 LIGHT NADP+ ADP LIGHT REACTOR CALVIN CYCLE ATP NADPH STROMA (Low H+ concentration) O 2 [CH 2 O] (sugar) Cytochrome complex Photosystem II Photosystem I NADP+ reductase Light 2 H+ Fd 3 NADPH Pq + H+ Pc 2 H 2 O THYLAKOID SPACE (High H+ concentration) NADP+ + 2 H+ 1⁄ 1 2 O 2 +2 H+ To Calvin cycle STROMA (Low H+ concentration) Thylakoid membrane ATP synthase ADP P ATP H+ Kemiosmosis adalah difusi ion yang melewati suatu membran. Proses ini berhubungan dengan pembentukan ATP karena pergerakan ion hidrogen yang melewati membran.

chemiosmosis 1. Inside thylakoid lumen, hydrogen ions (H+) accumulate from water splitting and from a coupling of the electron flow with an inward transfer of H+ from the stroma. The H+ being positively charged, this also makes the lumen more electropositive and the stroma more electronegative. 2. The combined concentration gradient and electric potential gradient make a free energy gradient for the H+, favouring their outward movement from the lumen into the stroma. 3. The thylakoid membrane is highly impermeable to H+. But it contains ATPsynthase enzyme complexes, with a proton channel through which the H+ move to the stroma, and this movement, down their free energy gradient, is coupled with ATP synthesis.

Reaksi Gelap atau Siklus Calvin • Senyawa gula dibentuk dari CO 2 (karbondioksida). • Fase ini tidak terlibat langsung dalam pemanfaatan cahaya. • Terjadi dalam stroma dari kloroplas.

Carbon Fixation • All plants carry on photosynthesis by adding carbon dioxide (CO 2) to a phosphorylated 5 -carbon sugar called ribulose bisphosphate. • This reaction is catalyzed by the enzyme ribulose bisphosphate carboxylase oxygenase (RUBISCO). • The resulting 6 -carbon compound breaks down into two molecules of 3 -phosphoglyceric acid (PGA). • These 3 -carbon molecules serve as the starting material for the synthesis of glucose and other food molecules. • The process is called the Calvin cycle and the pathway is called the C 3 pathway.

Siklus Calvin menggunakan ATP dan NADPH untuk mengkonversi CO 2 menjadi gula • Siklus calvin terjadi di stroma • Siklus Calvin memiliki 3 tahap – Fiksasi karbon – Reduksi – Regenerasi akseptor CO 2 (Ru. BP)

1 Sebuah molekul CO 2 dikonversi dari bentuk inorganiknya menjadi molekul organik (fixation) melalui pengikatan ke gula 5 C (ribulose bisphosphate atau Ru. BP). – Dikatalisasi oleh enzim Ru. BP carboxylase oxygenase (Rubisco). – Bentuk gula 6 C pecah menjadi 3 -phosphoglycerate 2 Tiap molekul 3 -phosphoglycerate menerima tambahan grup fosfat membentuk 1, 3 -Bisphoglycerate (fosforilasi ATP) NADPH dioksidasi dan elektron yang ditransfer ke 1, 3 Bisphoglycerate memecah molekul dengan tereduksi menjadi Glyceraldehyde 3 -phosphate 3 Tahap terakhir dari siklus ini adalah regenerasi Ru. BP Glyceraldehyde 3 -phosphate dikonversi menjadi Ru. BP melalui sebuah seri reaksi yang melibatkan fosforilasi molekul oleh ATP

Siklus Calvin Light H 2 O Input 3 (Entering one CO 2 at a time) CO 2 NADP+ ADP CALVIN CYCLE LIGHT REACTION ATP Phase 1: Carbon fixation NADPH O 2 Rubisco [CH 2 O] (sugar) 3 P P Short-lived intermediate 3 P P 6 P Ribulose bisphosphate (Ru. BP) 3 -Phosphoglycerate 6 ATP 6 ADP CALVIN CYCLE 3 ADP 3 ATP Phase 3: Regeneration of the CO 2 acceptor (Ru. BP) 6 P P 1, 3 -Bisphoglycerate 6 NADPH+ 6 P P 5 (G 3 P) 6 P Glyceraldehyde-3 -phosphate (G 3 P) P 1 G 3 P (a sugar) Output Glucose and other organic compounds Phase 2: Reduction

Siklus Calvin • Dimulai dari CO 2 dan menghasilkan 3 phosphoglycerate • Tiga bagian siklus Calvin menghasilkan 1 produk molekul • Tiga tahap – Fiksasi karbon – Reduksi CO 2 – Regenerasi Ru. BP

The Calvin cycle proceeds in three stages: 1. Carboxylation of the CO 2 acceptor ribulose-1, 5 -bisphosphate, forming two molecules of 3 -phosphoglycerate, the first stable intermediate of the Calvin cycle 2. Reduction of 3 -phosphoglycerate, forming gyceraldehyde- 3 phosphate, a carbohydrate 3. Regeneration of the CO 2 acceptor ribulose-1, 5 -bisphosphate from glyceraldehyde-3 -phosphate

C 4 Plants Help fight transpiration by keeping their stomata partially closed during the day and partially closed at night. Fix carbon dioxide into a temporary storage molecule that has four carbons It is called a C 4 pathway because the first stable compound that carbon dioxide is fixed into is a four carbon compound. The four carbon compound is transported to specialized cells where Calvin Cycle is taking place The four carbon compound releases carbon dioxide to run Calvin Cycle.

Tumbuhan C 4 • Senyawa yang terbentuk pertama kali setelah berikatan dengan CO 2 adalah senyawa berkarbon empat (oksaloasetat). • Tempat terjadinya fotosintesis terjadi di dua tempat yaitu sel mesofil (siklus C 3) dan seludang pembuluh (siklus C 4). • Tumbuhannya seperti sorgum, amaranthus, jagung. • Tumbuhan C 4 → kemampuan melaksanakan fotosintesis lebih tinggi dan lebih tahan terhadap kekeringan.

Tumbuhan C 4 • Tumbuhan C 4 meminimalkan keperluan fotorespirasi – dengan cara menggabungkan CO 2 ke dalam senyawa empat karbon di sel mesofil • Senyawa empat karbon tersebut – Dieksport ke seludang berkas pengangkut (cell bundle sheath), dimana CO 2 dilepaskan yang digunakan dalam siklus Calvin

C 4 Plants Corn, sugar cane and crab grass

C 4 Photosynthesis: The first fixation is a 4 -carbon compound

The basic C 4 cycle consists of four stages: 1. Fixation of CO 2 by the carboxylation of phosphoenolpyruvate in the mesophyll cells to form a C 4 acid (malate and/or aspartate) 2. Transport of the C 4 acids to the bundle sheath cells 3. Decarboxylation of the C 4 acids within the bundle sheath cells and generation of CO 2, which is then reduced to carbohydrate via the Calvin cycle 4. Transport of the C 3 acid (pyruvate or alanine) that is formed by the decarboxylation step back to the mesophyll cell and regeneration of the CO 2 acceptor phosphoenolpyruvate

The C 4 photosynthetic pathway

CAM Plants • Keep stomata CLOSED during the day and OPEN at night. • Store carbon dioxide as an organic acid. • The organic acid then releases carbon dioxide directly to the Calvin Cycle. • CAM plants grow very slowly, but they require less water than C 3 or C 4 plants.

Crassulacean acid metabolism (CAM) Temporal separation of CO 2 uptake from photosynthetic reactions: CO 2 uptake and fixation take place at night, and decarboxylation and refixation of the internally released CO 2 occur during the day. The adaptive advantage of CAM is the reduction of water loss by transpiration, achieved by the stomatal opening during the night. In both C 4 and CAM plants, PEP carboxylase is inhibited by malate and activated by glucose-6 -phosphate

Comparison C 3 Plants C 4 Plants CAM Plants Stomata Open during Day and Closed at Night Partially closed during day and partially closed at night Closed during day and Open at night Carbon fixation Carbon dioxide is “fixed” into a three carbon compound that is stable Carbon dioxide is spatially stored as a 4 carbon stable compound Carbon dioxide is temporarily stored as an organic acid. Water Loss Has trouble with water loss due to transpiration. Trouble with photorespiration Less water loss than C 3 plants. Photorespiration is not a problem Grow very slowly and no problems with photorespiration

SYNTHESIS OF STARCH AND SUCROSE

SYNTHESIS OF STARCH AND SUCROSE • Both starch and sucrose are synthesized from the triose phosphate that is generated by the Calvin cycle • Starch is synthesized in the chloroplast and starch in the cytosol • The relative concentrations of orthophosphate and triose phosphate are major factors that control whether photosynthetically fixed carbon is partitioned as starch in the chloroplast or as sucrose in the cytosol.

FOTORESPIRASI

RUBISCO Rubisco (D-ribulose-1, 5 -bisphosphate carboxylase/oxygenase) catalyzes the addition of carbon dioxide to D-ribulose-1, 5 bisphosphate to form two molecules of 3 -phospho-Dglycerate, the initial step in the C 3 photosynthetic carbon reduction cycle, and is the world’s most abundant enzyme. Rubisco has very strict specificity for the carbohydrate substrate, but it also catalyzes an oxygenase reaction in which O 2 replaces CO 2

• Rubisco has ability to catalyze both the carboxylation and the oxygenation of Ru. BP. • Photoinhibition is a complex set of molecular processes, defined as the inhibition of photosynthesis by excess light.

Photorespiration Higher plants, which fix carbon via the C 3 pathway, exhibit the process of photorespiration Rubisco catalyzes the fixation of both C 02 and O 2 Photorespiratory pathway involves the activities of at least three different cellular organelles (chloroplast, peroxisome, and mitochondrion

C 3 Photosynthesis : C 3 plants • Called C 3 because the CO 2 is first incorporated into a 3 carbon compound. • Stomata are open during the day. • RUBISCO, the enzyme involved in photosynthesis, is also the enzyme involved in the uptake of CO 2. • Photosynthesis takes place throughout the leaf. • Adaptive Value: more efficient than C 4 and CAM plants under cool and moist conditions and under normal light because requires less machinery (fewer enzymes and no specialized anatomy). • Most plants are C 3.

Anatomi daun C 4 dan jalur C 4 Photosynthetic cells of C 4 plant leaf Mesophyll cell Bundlesheath cell COCO 2 2 PEP carboxylase PEP (3 C) Oxaloacetate (4 C) ADP Vein (vascular tissue) Malate (4 C) ATP C 4 leaf anatomy Bundle. Sheath cell Pyruate (3 C) CO 2 Stoma CALVIN CYCLE Sugar Vascular tissue Pada tumbuhan C 4, seludang pembuluh – siklus Calvin proses fotosintesis

Tanaman CAM (Crassulacean Acid Metabolism) – Membuka stomatanya pada malam hari, menggabungkan CO 2 ke dalam asam organik – Selama siang hari, stomata tertutup CO 2 dilepaskan dari asam organik untuk digunakan dalam siklus Calvin Contoh tanaman C 4: kaktus, pineapple (bromeliads)

At night, • CAM plants take in CO 2 through their open stomata (they tend to have reduced numbers of them). • The CO 2 joins with PEP to form the 4 -carbon oxaloacetic acid. • This is converted to 4 -carbon malic acid that accumulates during the night in the central vacuole of the cells. In the morning, • the stomata close (thus conserving moisture as well as reducing the inward diffusion of oxygen). • The accumulated malic acid leaves the vacuole and is broken down to release CO 2. • The CO 2 is taken up into the Calvin (C 3) cycle. These adaptations also enable their owners to thrive in conditions of • high daytime temperatures • intense sunlight • low soil moisture.

Jalur CAM mirip dengan jalur C 4 Pineapple Sugarcane C 4 Mesophyll Cell Organic acid Bundlesheath cell (a) Spatial separation of steps. In C 4 plants, carbon fixation and the Calvin cycle occur in different types of cells. CALVIN CYCLE Sugar CAM CO 2 1 CO 2 incorporated into four-carbon organic acids (carbon fixation) 2 Organic acids release CO 2 to Calvin cycle CO 2 Organic acid Night Day CALVIN CYCLE Sugar (b) Temporal separation of steps. In CAM plants, carbon fixation and the Calvin cycle occur in the same cells at different times.

Sumber Pustaka Neil A. Campbell, Jane B. Reece. 8 th. 2008. Biology. Pearson Education, Inc. Öpik, H. & S. Rolfe 2005. The Physiology of Flowering Plants Fourth Edition. Cambridge University Press, Cambridge. UK Taiz, L. & E. Zeiger. 2002. Plant Physiology Third Edition. Sinauer Associates, Inc. Massachusetts.