Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings PowerPoint ® Lecture Presentations for Biology Eighth Edition Neil Campbell and Jane Reece Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp Chapter 10 Photosynthesis

Essential Knowledge: d. The light-dependent reactions of photosynthesis in eukaryotes involve a series of coordinated reaction pathways that capture free energy present in light to yield ATP and NADPH, which power the production of organic molecules. Evidence of student learning is a demonstrated understanding of each of the following: 1. During photosynthesis, chlorophylls absorb free energy from light, boosting electrons to a higher energy level in Photosystems I and II. 2. Photosystems I and II are embedded in the internal membranes of chloroplasts (thylakoids) and are connected by the transfer of higher free energy electrons through an electron transport chain (ETC). [See also 4.A.2] 3. When electrons are transferred between molecules in a sequence of reactions as they pass through the ETC, an electrochemical gradient of hydrogen ions (protons) across the thykaloid membrane is established. 4. The formation of the proton gradient is a separate process, but it is linked to the synthesis of ATP from ADP and inorganic phosphate via ATP synthase. 5. The energy captured in the light reactions as ATP and NADPH powers the production of carbohydrates from carbon dioxide in the Calvin cycle, which occurs in the stroma of the chloroplast. ✘✘ Memorization of the steps in the Calvin cycle, the structure of the molecules and the names of enzymes (with the exception of ATP synthase) are beyond the scope of the course and the AP Exam. e. Photosynthesis first evolved in prokaryotic organisms; scientific evidence supports that prokaryotic (bacterial) photosynthesis was responsible for the production of an oxygenated atmosphere; prokaryotic photosynthetic pathways were the foundation of eukaryotic photosynthesis.

Fig (a) Plants (c) Unicellular protist 10 µm 1.5 µm 40 µm (d) Cyanobacteria (e) Purple sulfur bacteria (b) Multicellular alga Photosynthetic Organisms:

Concept 10.1: Photosynthesis converts light energy to the chemical energy of food Chloroplasts are structurally similar to and likely evolved from photosynthetic bacteria The structural organization of these cells allows for the chemical reactions of photosynthesis 1 µm Chloroplast Cyanobacteria

Chloroplasts: The Sites of Photosynthesis in Plants Green structures on plants are the locations of photosynthesis Chlorophyll, the green pigment within chloroplasts captures energy from light Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 6 CO H 2 O + Light energy  C 6 H 12 O O H 2 O

Fig. 10-3a 5 µm Mesophyll cell Stomata CO 2 O2O2 Chloroplast Mesophyll Vein Leaf cross section Mesophyll: the interior tissue of the leaf Each Mesophyll cell contains on average chloroplasts

Fig. 10-3b 1 µm Thylakoid space Chloroplast Granum Intermembrane space Inner membrane Outer membrane Stroma Thylakoid Chloroplast Structure Large internal S.A. made by Thylakoid membrane. Thylakoid Space (lumen) inside the Thylakoid. Chlorophyll is imbedded in the Thylakoid Membrane. Stroma: a dense fluid surrounding the thylakoids.

The Two Stages of Photosynthesis: A Preview The light reactions (the photo part) and Calvin cycle (the synthesis part) Light reactions = in the Thylakoids – Light + H 2 O  O 2 + ATP and NADPH (e-carrier) Calvin cycle = in the stroma (carbon fixation) – CO 2 + ATP + NADPH  sugar Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 6 CO H 2 O + Light  C 6 H 12 O O H 2 O

Light Fig H2OH2O Chloroplast Light Reactions NADP + P ADP i +

Light Fig H2OH2O Chloroplast Light Reactions NADP + P ADP i + ATP NADPH O2O2

Light Fig H2OH2O Chloroplast Light Reactions NADP + P ADP i + ATP NADPH O2O2 Calvin Cycle CO 2

Light Fig H2OH2O Chloroplast Light Reactions NADP + P ADP i + ATP NADPH O2O2 Calvin Cycle CO 2 [CH 2 O] (sugar)

Fig THYLAKOID SPACE (INTERIOR OF THYLAKOID) STROMA e–e– Pigment molecules Photon Transfer of energy Special pair of chlorophyll a molecules Thylakoid membrane Photosystem Primary electron acceptor Reaction-center complex Light-harvesting complexes

Cyanobacteria Photosystem II Massive complex that includes protein, coenzymes, cofactors, and pigment molecules such as chlorophyll a, chlorophyll b, beta- carotene, and the primary electron acceptor pheophytin.

UV Fig Visible light Infrared Micro- waves Radio waves X-rays Gamma rays 10 3 m 1 m (10 9 nm) 10 6 nm 10 3 nm 1 nm 10 –3 nm 10 –5 nm nm Longer wavelength Lower energyHigher energy Shorter wavelength

Photosynthetic Pigments: The Light Receptors Pigments are substances that absorb visible light. Plants have two main pigments for absorbing light: – Chlorophyll a – Chlorophyll b Beta carotene is an accessory pigment that helps protect the plant from sun burn. Photosynthesis Lab: What color of light would power photosynthesis the most? Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Absorbance Wavelength of light (nm)

The Light Reactions: Photosystems II and I Photosystem II 1.Electrons are excited by light (wavelength of 680nm) 2.Splits H 2 O 3.Release O 2 4.Electrons (H + + 2e-) from H 2 O go through an electron transport chain to generate ATP (photophosphorylation) 5.Electrons are passed to Photosystem I Photosystem I 1.Electrons are excited by light (wavelength of 700nm) 2.Electrons passed down another ETC 3.Energized electrons are used to reduce NADP + to NADPH Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Pigment molecules Light P680 e–e– Primary acceptor 2 1 e–e– e–e– 2 H + O2O2 + 3 H2OH2O 1/21/2 4 Pq Pc Cytochrome complex Electron transport chain 5 ATP Photosystem I (PS I) Light Primary acceptor e–e– P700 6 Fd Electron transport chain NADP + reductase NADP + + H + NADPH 8 7 e–e– e–e– 6 Fig Photosystem II (PS II) Linear Flow of Electrons in The light reaction generates NADPH

Pigment molecules Light P680 e–e– 2 1 Fig Photosystem II (PS II) Primary acceptor A photon hits a pigment and its energy is passed among pigment molecules until it excites P680 An excited electron from P680 is transferred to the primary electron acceptor (Pheophytin)

Pigment molecules Light P680 e–e– Primary acceptor 2 1 e–e– e–e– 2 H + O2O2 + 3 H2OH2O 1/21/2 Fig Photosystem II (PS II) P680 + (P680 that is missing an electron) is a very strong oxidizing agent H 2 O is split by enzymes, and the electrons are transferred to P680 +, reducing it to P680. O 2 is released as a by- product of this reaction

Pigment molecules Light P680 e–e– Primary acceptor 2 1 e–e– e–e– 2 H + O2O2 + 3 H2OH2O 1/21/2 4 Pq Pc Cytochrome complex Electron transport chain 5 ATP Fig Photosystem II (PS II) The electrons are passed through an electron transport chain (Cytochrome complex). ETC uses electrons to pump H+ into thylakoid Chemiosmosis of H + out of thylakoid space through ATP Synthase drives ATP synthesis. This is photophosphorylation PSII ETC PSI H+ H+ H+ ATP

Fig Pigment molecules Light P680 e–e– Primary acceptor 2 1 e–e– e–e– 2 H + O2O2 + 3 H2OH2O 1/21/2 4 Pq Pc Cytochrome complex Electron transport chain 5 ATP Photosystem I (PS I) Light Primary acceptor e–e– P700 6 Photosystem II (PS II) Light excites P700, which loses an electron to an electron acceptor (becoming P700+) P700 + accepts an electron passed down from Pc.

Fig Pigment molecules Light P680 e–e– Primary acceptor 2 1 e–e– e–e– 2 H + O2O2 + 3 H2OH2O 1/21/2 4 Pq Pc Cytochrome complex Electron transport chain 5 ATP Photosystem I (PS I) Light Primary acceptor e–e– P700 6 Fd Electron transport chain NADP + reductase NADP + + H + NADPH 8 7 e–e– e–e– 6 Photosystem II (PS II) Electrons pass through another ETC to NADP+, reducing it to NADPH. The electrons of NADPH are available for the reactions of the Calvin cycle

Fig Mill makes ATP e–e– NADPH Photon e–e– e–e– e–e– e–e– e–e– ATP Photosystem IIPhotosystem I e–e–

Fig ATP Photosystem II Photosystem I Primary acceptor Pq Cytochrome complex Fd Pc Primary acceptor Fd NADP + reductase NADPH NADP + + H + Uses only Photosystem I and produces ATP, but not NADPH Generates surplus ATP, satisfying the higher demand in the Calvin cycle Cyclic Electron Flow

Fig Light Fd Cytochrome complex ADP + i H+H+ ATP P synthase To Calvin Cycle STROMA (low H + concentration) Thylakoid membrane THYLAKOID SPACE (high H + concentration) STROMA (low H + concentration) Photosystem II Photosystem I 4 H + Pq Pc Light NADP + reductase NADP + + H + NADPH +2 H + H2OH2O O2O2 e–e– e–e– 1/21/

Light H2OH2O Chloroplast Light Reactions NADP + P ADP i + ATP NADPH O2O2 Calvin Cycle CO 2 [CH 2 O] (sugar) Concept 10.3: The Calvin cycle uses ATP and NADPH to convert CO 2 to sugar The Calvin cycle: Occurs in the Stroma 3CO 2 + ATP + NADPH  1G3P (a 3 Carbon sugar: C 3 H 7 O 6 P)

The Calvin Cycle 3 Phases of the Calvin Cycle – 1) Carbon Fixation CO 2 is attached to a 5C precursor by the enzyme Rubisco – 2) Reduction H + + e - from NADPH are attached to the 3 C sugar G3P (3C sugar) leaves the cycle to form sugar/ organic compounds – 3) Regeneration of 5 carbon precursor Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig Ribulose bisphosphate (RuBP) 3-Phosphoglycerate Short-lived intermediate Phase 1: Carbon fixation (Entering one at a time) Rubisco Input CO 2 P P P P P

Fig Ribulose bisphosphate (RuBP) 3-Phosphoglycerate Short-lived intermediate Phase 1: Carbon fixation (Entering one at a time) Rubisco Input CO 2 P P P P P ATP 6 6 ADP P P 6 1,3-Bisphosphoglycerate 6 P P NADP + NADPH i Phase 2: Reduction Glyceraldehyde-3-phosphate (G3P) 1 P Output G3P (a sugar) Glucose and other organic compounds Calvin Cycle

Fig Ribulose bisphosphate (RuBP) 3-Phosphoglycerate Short-lived intermediate Phase 1: Carbon fixation (Entering one at a time) Rubisco Input CO 2 P P P P P ATP 6 6 ADP P P 6 1,3-Bisphosphoglycerate 6 P P NADP + NADPH i Phase 2: Reduction Glyceraldehyde-3-phosphate (G3P) 1 P Output G3P (a sugar) Glucose and other organic compounds Calvin Cycle 3 3 ADP ATP 5 P Phase 3: Regeneration of the CO 2 acceptor (RuBP) G3P

Photosynthesis Summary Light Reactions (In the thylakoid/ across the thylakoid memebrane) Photosystem II 1.P680 reaction center Electrons are excited by light (wavelength of 680nm) 2.Splits H 2 O 3.Release O 2 4.Electrons (H + + 2e-) from H 2 O go through an electron transport chain Protons are pumped into the lumen of the Thylakoid (Thylakoid space) Protons exit through ATP Synthase to generate ATP (photophosphorylation) 5.Electrons are passed to Photosystem I Photosystem I (P700) 1.Electrons are excited by light (wavelength of 700nm) 2.Electrons passed down another ETC 3.Energized electrons are used to reduce NADP + to NADPH The Calvin Cycle (Stroma of the Chloroplast) 1.Carbon Fixation CO 2 is attached to a 5C precursor by the enzyme Rubisco 2.Reduction of Carbon H + + e - from NADPH are attached to the 3 C sugar G3P (3C sugar) leaves the cycle to form sugar or other organic compounds 3.Regeneration of 5 carbon precursor