2. Lecture 4 Outline (Ch. 10, 11) I.Light reactions A. Photosystems B. Photophosphorylation II.The light independent reactions (“dark” rxn) A. Carbon “fixation” B. Reduction C. Regeneration III.Cell Signaling A. Signal Transduction B. Phosphorylation C. Example signals IV.Preparation for next lecture

3. Light Reaction Review Light H2OH2O Chloroplast Light Reactions NADP + P ADP i + ATP NADPH O2O2 Calvin Cycle CO 2

4. Photosynthesis – light absorption light energy absorbed by pigments, transferred to reaction center - two special chlorophyll a - 1° electron acceptor Pigments held by proteins in thylakoid membranes TWO Photosystems (PS)

5. Photosynthesis – Photosystems PSII: more powerful PS, longer ETC, e- replaced from splitting water PS I: lower energy PS, short ETC  NADPH made, e- replaced from PSII

6. Photosynthesis – Photosystems Photosystem IIPhotosystem I

7. Which photosystem is more powerful? A.PSII – can split water B.PS I – makes NADPH C.PSII – absorbs energy from PSI D.PSI – can make ATP E.Both equal

8. PS___ ? Electron Transport System ____ ____ PS___ ? Electron Transport System ? _____ ? On the Spot Problem Solar energy ___

9. PS II e-e- Electron Transport System ATP ATP PS I e-e- Electron Transport System e-e- NADPH e-e- H2OH2OO2O2 Light Dependent Reactions Solar energy

10. “Dark” reaction (Light-independent Reaction) CO 2 + H 2 O + light energy C 6 H 12 O 6 + O 2 “Dark” reaction: Calvin cycle regenerative anabolic CO 2 in, sugar out during daylight CO 2 NADP + ADP P i + RuBP 3-Phosphoglycerate Calvin Cycle G3P ATP NADPH Starch (storage) Sucrose (export) Chloroplast Light H2OH2O O2O2

11. What happens to CO 2 in the “dark” reaction? A.Oxidized to glucose B. Reduced to glucose C. Oxidized to water D. Reduced to water E. CO2 is not used in the “dark” reaction

12. Carbon fixation 3 stages of Calvin-cycle: CO 2 link to 5-C 5-C: ribulose bisphosphate (RuBP) - enzyme: Rubisco 6-C unstable – split  2(3-C)

13. 3 stages of Calvin-cycle: Reduction reduced 3-C: G3P one leaves, 5 continue 3-C reduced e- from NADPH

14. Requires THREE turns of the whole cycle!!! Regeneration of C-acceptor multiple steps uses ATP every 3 cycles: 1 G3P made 3 RuBP regenerated still 5 G3P  3 RuBP 3 stages of Calvin-cycle:

15. Calvin Cycle

16. _____ “Photo” = ____________ “Synthesis” = ____________ _____ Self-Check

17. light ATP NADPH H2OH2OO2O2 Light-dependent reactions Light-independent reactions (Calvin (C3) Cycle) CO 2 glucose ADP NADP+

18. ? ? ? _____ ______ _____ Calvin (C3) Cycle: Where? energy from light dependent reactions 1 2 3 Self-Check

19. RuBP PGA G3P CO 2 ATP ADP Glucose NADPH NADP+ ATP ADP Calvin (C3) Cycle: In the stroma energy from light dependent reactions 1 2 3 Light Independent Reactions

20. Photosynthesis – summary light reaction: Light energy + H 2 O IN light-independent: CO 2, NADPH, ATP IN O 2, NADPH, ATP OUT Thylakoids G3P (sugar), RuBP OUT Stroma KNOW THIS FIGURE!

23. Cell Signaling = Signal Transduction Signal Transduction – receiving a signal & relaying the response

24. Reception Transduction Response Receptor Relay molecules Signaling molecule Activation of cellular response 1 2 3 Signal Transduction Cell phone rings You listen to your friend You drive somewhere Response variable – examples: mate, organize, divide, die, grow, send another signal, etc…

25. Sending the Signal Four methods of cell signaling:

26. Signal Transduction Signaling-molecule binding site Segment that sends signal inside cell The receptor is a protein that detects the signal Signal called a ligand

27. Signal Transduction for hydrophobic molecules Receptor protein Hormone (testosterone) EXTRACELLULAR FLUID Plasma membrane Hormone- receptor complex DNA Hormone (testosterone) EXTRACELLULAR FLUID Receptor protein Plasma membrane Hormone- receptor complex DNA NUCLEUS CYTOPLASM hydrophobic signals - Receptor moves to DNA

28. Transduction – relay the signal Phosphorylation: adding a phosphate group Used to activate proteins already in the cell

29. Transduction hydrophilic signals – relay the signal Dephosphorylation = removing a phosphate group

30. Signaling molecule Receptor Activated relay molecule Inactive protein kinase 1 Active protein kinase 1 Inactive protein kinase 2 ATP ADP Active protein kinase 2 P P PP Inactive protein kinase 3 ATP ADP Active protein kinase 3 P P PP i ATP ADP P Active protein PP P i Inactive protein Cellular response Phosphorylation cascade i hydrophilic signals Receptor alerts molecules inside the cell = phosphorylation Signal Transduction for hydrophilic molecules

31. First messenger G protein Adenylyl cyclase GTP ATP cAMP Second messenger Protein kinase A G protein-coupled receptor Cellular responses Or use second messengers = small molecules inside cell to relay message example second messengers: GTP, cAMP, ATP, Ca++ Signal Transduction for hydrophilic molecules

32. If glucose were a signal molecule (ligand), how would it work? A.Diffuse through the cell membrane and bind cytoplasmic receptor B.Move through the cell membrane and add phosphates to other molecules C.Bind an extracellular receptor at the plasma membrane

33. Interdigital tissue 1 mm Response – cell does something

34. protein (active) Inhibits activity Mitochondrion Receptor for death- signaling molecule Inactive proteins (a) No death signal Response – ex. No death signal, cell lives

35. (b) Death signal Death- signaling molecule (inactive) Cell forms blebs Active Activation cascade Other proteases Nucleases Response – ex. Death signal, cell undergoes apoptosis

36. Growth factor Receptor Phosphorylation cascade Reception Transduction Active transcription factor Response P Inactive transcription factor CYTOPLASM DNA NUCLEUS mRNA Gene Signal transduction = reception, transduction, response

37. Things To Do After Lecture 4… Reading and Preparation: 1.Re-read today’s lecture, highlight all vocabulary you do not understand, and look up terms. 2.Read chapter 10 & 11, focus on material covered in lecture (terms, concepts, and figures!) 3.Ch. 10 Self-Quiz: # #1, 2, 5, 7; Ch. 11 Self-Quiz: #1,4,6 (correct using the back of the book). 4.Skim next lecture. “HOMEWORK” (basis for potential “POP HOMEWORK”): 1.Write the overall reaction for photosynthesis and indicate which parts constitute the light reaction inputs and outputs. 2.Draw and label a simple chloroplast and diagram where PSI & II are located, and where the Calvin cycle happens. 3.Compare and contrast PSI and PSII. 4.Explain the Calvin Cycle in your own words, emphasizing the three main steps/stages. 5.Describe signal transduction for hydrophilic and hydrophobic molecules.

38. Preparing for Exam I Chapters Covered: Ch. 7 – Cell Membranes Ch. 8 – Metabolism, Energy & Enzymes Ch. 9 – Cell Respiration and Fermentation Ch. 10 – Photosynthesis Ch.11 – Cell Communication Review end-of-chapter problems Go over “homework” questions Practice problems and study aids for exam I on website