Botany 251Y Part II Powerpoint Animations for the Photosynthesis lectures Directions: Play the Powerpoint show, and click enter to move to the next step in the animation, or the next slide.

LIGHT ABSORBTION AND TRANSFER TO THE REACTION CENTERS

NADP reductase 2H 2 O O 2 + 4H + 2H + + 2NADP NADPH 4 e - 4 photons 2 H + CYT B 6 f PC PSI PSII Fd The Path of Electron and Proton Flow in Photosynthetic Electron Transport PQ

NADP reductase 2 H + 4 H + CYT B 6 f PC PSI PSII PQ Fd CYCLIC PHOTOPHOSPHORYLATION Under conditions where NADP + regeneration is slow, or ATP demand is high, the leaf can cycle electrons between plastoquinone and PSI, and in doin so pump protons across the membrane. This is termed cyclic photophosphrylation.

PHOTOSYSTEM I H+ H+ H + H+ H+ H + H+ H+ H + H+ H+ H + H+ H+ H + H+ H+ H + H+ H+ H + H+ H+ H + H+ H+ H + H+ H+ H + H+ H+ H + H+ H+ H + H+ H+ H + H+ H+ H + H+ H+ H + H+ H+ H + H+ H+ H + H+ H+ H + H+ H+ H + H+ H+ H + H+ H+ H + H+ H+ H + H+ H+ H + H+ H+ H + H+ H+ H + H+ H+ H + H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ ADP + P i ATP 3 H + Thylakoid Lumen – compartment of low pH Chloroplast stroma – region of high pH PHOTOPHOSPHORYLATION ATP Synthase (F-type ATPase)

Phase 1: Carboxylation RuBP (5 carbon) + CO2 2 PGA (3 carbon) RUBISCO Note: The oxygen in CO 2 is incorporated into one of the PGA molecules. It is not released as O 2.

Properties of Rubisco (Ribulose-1,5-bisphosphate carboxylase/oxygenase) In primitive photosynthetic bacteria, Rubisco exists as a dimer of two subunits In the evolution of the blue- green algae, the primitive, two-subunit form of Rubisco was modified by the combination of 4 dimers to give a complex of 8 subunits in four pairs of dimers.

RuBP Oxygenation RuBP (5 carbon) + O 2 RUBISCO PGA + PG