Didik Pudji Restanto UPN Sby Agronomi 1988 IPB Bogor Fisiologi Tumbuhan 1991James Cook University Australia Fisiologi Molekuler 2003 Staf AgronomiLaboratorium Biologi Molekuler Unej

MATERI KULIAH Fotosinthesis (2) Perbedaan Tanaman C3, C4 dan CAM (1) Respirasi (1) Fotorespirasi (1) Ensim Carbonic anhydrase (CA) (1) Diskusi Jurnal (3) Format :* Buatlah artikel sederhana 4 halaman yang berisi tentang data penelitian orang lain dan saudara bahas.* Artikel dikumpulkan saat kuliah CA

PENILAIAN :Scor 80 %(Nilai Kuis I + kuis II + Jurnal + UAS) 4Skor 20%Praktikum

PhotosinthesisBy Didik Pudji Restanto

Summary Photosynthesis Reaction6 CO2 + 6 H2O C6H12O6 + 6 O2

LightBright sunlight = 2000 mol m-2 s-1 (approximately 10,000 fc)

C3 plants can use up to (~ 700 mol m-2 s-1)C4 plants can use up to (~ 2000 mol m-2 s-1 )

Photosynthesis: overall reactionWhat we need to make glucose:CarbonOxygenHydrogenEnergy

The Two Phases of PhotosynthesisLight Reactions (aka: Z Scheme)Photolysis (H2O 2H+ + 1/2O2)Photophosphorylation (ADP + P ATP)NADP Reduction (NADP + H+ NADPH)Dark Reactions (aka: C3 or Calvin-Benson Cycle)Carbon Dioxide Fixation (CO2 C6H12O6)

Chemiosmotic formation of ATP

Z-SCHEME DIAGRAM

Mechanism of CO2 Absorption and TransportCO2CO2 + H2O H2CO3 (carbonic acid)H2CO3 + Na+ NaHCO3 (K+ also works)NaHCO3 Na+ + HCO3-

Light-independent reactions (Calvin-Benson cycle)RuBisCOSubstrates:

Products:

C4 Type

C3 Photosynthesis not as Efficient as C4No CO2 pump (PEP carboxylase more efficient than Rubisco)PhotorespirationUp to 50% of fixed CO2 (RuBP) entering Rubisco can be converted back to PGA and phosphoglycolate (which goes to CO2)Occurs only in lightRuBP Carboxylase acts as an Oxygenase

Illustration of the four major protein complexes on the thylakoid membrane and the Calvin-Benson cycle in the stroma

CO2 combines with phosphoenol pyruvate (PEP) in mesophyll cells, forming a four-carbon compound that is converted to malate. Malate goes to the bundle sheath cell, where it is decarboxylated. The CO2 thus released in the bundle sheath cell is used to make sugar by way of the Calvin cycle. Because the C4 system consumes some energy, ultimately made available only by photosynthesis, this system is important to the plant only at high light intensities. Under these conditions, it can fix more carbon than the C3 system can fix by itself.

Figure: 07.5

Title:Oxygen is a by-product of photosynthesis

Caption:The bubbles released by the leaves of this aquatic plant (Elodea) are composed of oxygen, a by-product of photosynthesis.Figure: 07.4

Title:Thylakoid structure and the light-dependent reactions of photosynthesis

Caption:A summary of the light-dependent reactions. 1) Light is absorbed by the light-harvesting complex of photosystem II, and the energy is passed to the reaction-center chlorophyll molecule. 2) This energy ejects electrons out of the reaction center. 3) The electrons pass to the adjacent electron transport system. 4) The transport system passes the energetic electrons along, and some of their energy is used to pump hydrogen ions into the thylakoid interior. The hydrogen ion gradient thus generated can drive ATP synthesis. 5) Light strikes photosystem I, causing it to emit electrons. 6) The electrons are captured by the photosystem I electron transport system. The electrons lost from the reaction center of photosystem I are replaced by those from the transport system of photosystem II. 7) The energetic electrons from photosystem I are captured in molecules of NADPH. 8) The electrons lost from the reaction center of photosystem II are replaced by electrons obtained from splitting water. This reaction also releases oxygen. Figure: 07.Un02

Title:Light-dependent and light independent reactions

Caption:Light-dependent and light independent reactions of photosynthesis.Figure: 07.1

Title:Interconnections between photosynthesis and cellular respiration

Caption:Chloroplasts in green plants use the energy of sunlight to synthesize high-energy carbon compounds such as glucose from low-energy molecules of water and carbon dioxide. Plants themselves, and other organisms that eat plants or one another, extract energy from these organic molecules by cellular respiration, yielding water and carbon dioxide once again. This energy in turn drives all the reactions of life. Figure: 07.UN05b

Title:Chemiosmosis: synthesizing ATP

Caption:Chemiosmosis: synthesizing ATPFigure: 07.UN05a

Title:Chemiosmosis: developing a proton gradient

Caption:Chemiosmosis: developing a proton gradient.Figure: 07.UN03

Title:Light-dependent reactions of photosynthesis

Caption:Light-dependent reactions of photosynthesis.Figure: 07.2

Title:An overview of photosynthetic structures

Caption:Photosynthesis occurs in chloroplasts, which are located primarily in the leaves of land plants (a). A section of a leaf is shown (b) with a single chloroplast isolated and enlarged (c). Figure: 07.7

Title:A summary diagram of photosynthesis

Caption:The light-dependent reactions in the thylakoids convert the energy of sunlight into the chemical energy of ATP and NADPH. Part of the sunlight energy is also used to split H2O, forming O2 . In the stroma, the light-independent reactions (C3 cycle) use the energy of ATP and NADPH to convert CO2 and H2O to glucose. The depleted carriers, ADP and NADP+ , return to the thylakoids to be recharged by the light-dependent reactions.Figure: 07.8a

Title:Comparison of C3 and C4 plants: C3 plants

Caption:In C3 plants, only the mesophyll cells carry out photosynthesis. All carbon fixation occurs by the C3 pathway. With low CO2 and high O2 levels, photorespiration dominates in C3 plants, because the enzyme that should catalyze the RuBP CO2 reaction catalyzes the RuBP O2 reaction instead. Figure: 07.8b

Title:Comparison of C3 and C4 plants: C4 plants

Caption: In C4 plants, both the mesophyll cells and bundle-sheath cells contain chloroplasts and participate in photosynthesis. The initial carbon-fixation step in the mesophyll cells is a reaction between phosphoenolpyruvic acid (PEP) and CO2 , with which O2 does not compete. A four-carbon molecule of oxaloacetate is produced and releases CO2 in the bundle-sheath cells, thus maintaining a high CO2 concentration in their chloroplasts. Higher CO2 levels allow efficient carbon fixation in the C3 pathway of the bundle-sheath cells with little photorespiration. Notice that the regeneration of PEP requires energy: Two phosphates are removed from ATP to produce AMP (adenosine monophosphate).