Photosynthesis: The Light Reactions Part 2 of 4

Original video: https://youtu.be/dYs_TczAsM0

Delivered on: 16 OCTOBER 2023

This video provides a foundational understanding of photosynthesis, focusing on the crucial light-dependent reactions that occur within chloroplasts. 🌿 We'll explore key experiments, the organization of the photosynthetic apparatus, and how light energy is captured and converted into chemical energy.

What you'll learn:

• Key Experiments in Photosynthesis:  We'll examine landmark experiments that revealed the action spectrum of photosynthesis, the role of antenna pigments, and the two-photosystem model (PSI and PSII) in oxygen-evolving organisms.

• Organization of the Photosynthetic Apparatus:  Explore the intricate structure of chloroplasts, including thylakoid membranes, grana, stroma lamellae, and the spatial separation of PSI and PSII.

• Light-Absorbing Antenna Systems:  Understand how antenna complexes capture light energy and funnel it to reaction centers for efficient photochemistry.

• Mechanisms of Electron Transport:  We'll introduce the Z-scheme, a model that illustrates the flow of electrons from water to NADP+ through photosystems and electron carriers.

Video Timestamps for Easy Navigation:

• 3:40 Action spectrum measurement by T.W. Engelmann using Spirogyra

• 6:13 Light absorption by plant pigments

• 10:15 Quantum yield

• 13:53 Light drives the function of NADP+ and the formation of ATP

• 18:28 Organization of the photosynthetic apparatus

• 20:15 Chloroplast structure

• 25:00 Web essay for further learning

• 26:24 Thylakoids contain integral membrane proteins

• 30:34 Photosystems I and II are spatially separated

• 39:16 Schematic diagram of integral membrane

• 44:44 Anoxygenic photosynthetic bacteria

• 47:15 Structures of two bacterial reaction centers

• 48:21 Quiz

• 50:10 Organization of light-absorbing antenna systems

• 53:50 The antenna funnels energy to the reaction center

• 1:00:09 Antenna pigment-protein complexes

• 1:03:17 Mechanisms of electron transport, Z-scheme

9.3 Key Experiments in Understanding Photosynthesis

An action spectrum for photosynthesis shows algal oxygen evolution at certain wavelengths (Figures 9.8, 9.9).

Antenna pigment–protein complexes collect light energy and transfer it to the reaction center complexes (Figures 9.10, 9.16).

Light drives the reduction of NADP+ and the formation of ATP. Oxygen-evolving organisms have two photosystems (PSI and PSII) that operate in series (Figure 9.12).

9.4 Organization of the Photosynthetic Apparatus

Within the chloroplast, thylakoid membranes contain the reaction centers, the light-harvesting antenna complexes, and most of the electron carrier proteins.

PSI and PSII are spatially separated in thylakoids (Figure 9.15).

9.5 Organization of Light-Absorbing Antenna Systems

The antenna system funnels energy to the reaction center (Figure 9.16).

Light-harvesting proteins of both photosystems are structurally similar (Figure 9.17).

LIST OF KEY TERMS

1. absorption spectrum

2. accessory pigments

3. action spectrum

4. antenna complex

5. ATPase

6. ATP synthase

7. bacteriochlorophylls

8. bleached

9. carbon fixation reactions

10. carotenoids

11. CF0–CF1

12. charge-separated state

13. chemical potential

14. chlorophyll a/b antenna proteins

15. chlorophylls

16. cyclic electron flow

17. cytochrome b6f complex

18. cytochrome f

19. endosymbiosis

20. energy conversion efficiency

21. energy transfer

22. envelope

23. ferredoxin (Fd)

24. ferredoxin–NADP+ reductase (FNR)

25. FeSA

26. FeSB

27. Fe–S centers

28. FeSX

29. fluorescence

30. fluorescence resonance energy transfer

31. frequency

32. grana lamellae

33. integral membrane proteins

34. light energy

35. light-harvesting complex II (LHCII)

36. lowest excited state

37. non-Mendelian, or maternal, inheritance

38. Nonphotochemical quenching

39. oxygen-evolving complex (OEC)

40. P680

41. P700

42. P870

43. Pheophytin

44. photochemistry

45. Photoinhibition

46. photons

47. photophosphorylation

48. photoprotection

49. photosystems I and II (PSI and PSII)

50. plastocyanin (PC)

51. plastohydroquinone (PQH2)

52. proton motive force

53. Q cycle

54. quanta

55. quantum yield

56. quenched

57. reaction center complex

58. reactive oxygen species

59. Rieske iron–sulfur protein

60. singlet oxygen

61. stroma

62. stroma lamellae

63. thylakoid reactions

64. thylakoids

65. transit peptide

66. uncoupled

67. wavelength

68. xanthophylls

Location:

Faculty of Agriculture, Universiti Putra Malaysia

Fakulti Pertanian, Universiti Putra Malaysia, 43000 Seri Kembangan, Selangor

https://maps.app.goo.gl/QktwYFWyzdcwow148

XPMM+9J Seri Kembangan, Selangor

2.9845517506267742, 101.73803356324866

Attribution 4.0 International — CC BY 4.0 - Creative Commons