1. PACKET #31 CHAPTER #10 The Light Reactions Non-cyclic Electron Flow

2. Introduction I The goal of the light reactions is to produce ATP and NADPH via the movement of electrons  Solar energy is converted into chemical energy.  The ATP, and NADPH, produced is used in the Calvin Cycle.  The movement of electrons is similar to that of oxidative phosphorylation  Cellular respiration.

3. Another View

4. Introduction II Non-cyclic flow requires the use of  Photosystems  Photosystem II  Photosystem I  Mobile electron acceptors  Plastoquinone  Plastocyanin  Ferrodoxin  Stationary electron acceptor  Cytochrome B6F  Enzymes  Ferrodoxin-NADP+ reductase  ATP synthase

5. Introduction III 10/20/2015 5 To effectively understand the non-cyclic electron flow, one must remember the “key.”  Electrons are moved and ultimately stored in NADPH.

6. The Photosystems

7. Photosystems—Part I The light reactions involve the use of photosystems. The photosystems, absorb different wavelengths of light within their chlorophyll molecules. This absorption allows for the excitation and movement of electrons.

8. Photosystems—Part II Photosystem II  Absorbs light with wavelengths of 680 nM  Yellow-green light Photosystem I  Absorbs light with wavelengths of 700 nM  Red light

9. THE PROCESS Non-Cyclic Electron Flow

10. Non-cyclic Electron Flow Step by Step I Photon, of 680nm, hits ONE of the many chlorophyll molecules found in photosystem II. This causes an electron to become excited.

11. Non-cyclic Electron Flow Step by Step II The excited electron moves along multiple chlorophyll molecules until it reaches the reaction center.

12. Non-cyclic Electron Flow Step by Step III The excited electron arrives and waits at the primary electron acceptor until it is picked up by the mobile electron carrier plastoquinone.

13. Non-cyclic Electron Flow Step by Step IV Plastoquinone has the ability to carry two electrons and waits until a second electron becomes available.

14. Non-cyclic Electron Flow Step by Step V The second electron originates from H 2 O.  Once an electron leaves photosystem II, it has to be replaced. Water is broken into  H +  The hydrogen ion is used to help establish the hydrogen gradient inside the thylakoid space.  O 2  Eventually leaves the leaf through the stomata.  An electron  This electron fills in the gap made by the electron that has boarded plastoquinone.

15. Non-cyclic Electron Flow Step by Step VI The second electron, now residing in a chlorophyll molecule of photosystem II, becomes excited by a another photon of 680nm.

16. Non-cyclic Electron Flow Step by Step VII The second electron eventually boards plastoquinone to join the electron that previously boarded. The gap produced again by a missing electron is replaced when another molecule of water is broken.

17. Non-cyclic Electron Flow Step by Step VIII The two electrons, and two hydrogen ions, in plastoquinone are transported to the stationary electron acceptor cytochrome B6F.

18. Non-cyclic Electron Flow Step by Step IX The two electrons and two hydrogen ions enter the stationary electron acceptor cytochrome B6F.

19. Non-cyclic Electron Flow Step by Step X Once both the electrons and the two H + are inside cytochrome B6F, the cytochrome opens it’s H + channel gate and allows the H + to leave, through the channel, freely into the thylakoid space.  The H +, once in the thylakoid space, helps strengthen the hydrogen gradient.  Chemiosmosis

20. Non-cyclic Electron Flow Step by Step XI Meanwhile, as the H + ions enter into the thylakoid space, the two electrons board the second mobile electron acceptor called plastocyanin.

21. Non-cyclic Electron Flow Step by Step XII Plastocyanin takes the two electrons to photosystem I.

22. Non-cyclic Electron Flow Step by Step XIII The electrons, once in photosystem I, are re- excited with a photon of wavelength 700nm.  Experience similar process as seen in photosystem II.

23. Non-cyclic Electron Flow Step by Step XIV The two electrons leave photosystem I and board the third mobile electron acceptor ferredoxin.

24. Non-cyclic Electron Flow Step by Step XV Ferredoxin transports the two electrons to the enzyme ferrodoxin- NADP + reductase. The enzyme transfers the electrons to the electron acceptor NADP + for transport to the Calvin Cycle.  NADP + is changed into NADPH.

25. Non-cyclic Electron Flow Step by Step XVI But wait…there is more… The hydrogen ions, that were used to produce the hydrogen gradient in the thylakoid space, are pumped into the stroma via ATP synthase.  Each hydrogen ion that passes through ATP synthase produces 1 ATP.  The ATP is then used in the Calvin Cycle.

26. Overall Review

27. “Overall” Inputs & Outputs Non-Cyclic Electron Flow 10/20/2015 27 Inputs  Light  NADP+  ADP  P  H 2 O Outputs  ATP  NADPH  O 2