Photosynthesis – the Light and Dark Reactions

Outer membrane Inner membrane Stroma Thylakoids Granum Light-dependent reactions take place in the thylakoid membrane The light reactions change the electromagnetic energy from light into chemical energy in the form of ATP and NADPH Photosynthesis takes place in chloroplasts Overview Movie – Click Me

THE EM Spectrum

PS Pigments

Photosynthesis is a two-step process n ATP and NADPH are used in the stroma (cytoplasm of the chloroplast) to fuel the Dark Reaction They provide chemical energy for the reactions Light ReactionDark Reaction ( Calvin Cycle)

Ribose Adenine Phosphate groups Ribose Adenine ATP consists of adenine, ribose, and three phosphate groups. High energy bonds

ATP + Energy ADP Water PPPP P PiPi Inorganic phosphate + H2OH2O ++ Figure 6.1b Energy is released when ATP is ripped apart

Reduction Oxidation NADPH (electron carrier Or charged battery) NAD+ (empty battery) NAD+ Is an energy carrying molecule in plants that must be recharged in the Light Reaction

Photosynthesis takes place in Chloroplasts Chlorophyll and accessory (helper) pigments capture electromagnetic energy by absorbing photons of light MOVIE CLICK ME

The Light Reactions Lead to the Formation of ATP and NADPH n ATP is the primary product of Photosystem II n NADPH is formed after electron excitation in Photosystem I

Photon Chlorophyll molecules Reaction center Photon Light Reaction – Step 1 Chlorophyll molecules transmit energy from excited electrons to a reaction center.

Higher Lower Energy of electron Chlorophyll Photon e–e– Carrier #1 #2 Electron transport chain Carrier #3 In photosystem II, excited electrons feed an electron transport chain. Energy put to work

PQ H+H+ 2e – H+H+ NAD  NADPH

Oxidation of H 2 O provides electrons 2 H 2 O --> 4 H e - + O 2 n Photosystem II is the only known protein complex that can rip apart (oxidize) water n All of the earth’s oxygen originates this way!!!!!!!!!!!

The energy from light is captured and converted in chloroplasts This energy is passed through an electron transport chain in chloroplasts that convert that energy to a more usable chemical form = ATP and NADPH

PHOTOSYSTEM II -- a Funky 3D Visualization

Photo- system II Cytochrome complex Photo- system I H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ Stroma Granum Found in membrane facing inside of grana ATP synthase Found in membrane facing stroma Equally common in both types of membrane Hey Bleecker! Where’s the ATP come From?? Well – the secret lies in these little ATPase Enzymes also found in the membrane

H+H+ H+H+ H+H+ H+H+ H+H+ THE STRUCTURE Of Enzyme ATP SYNTHASE Inside Thylakoid Chloroplast Stroma H+H+ ADP + P i ATP Rod F 1 unit F O unit H 2 O torn apart donates loads of Hydrogen which is useful to make ATP +

Here’s a little movie summarizing ATP synthesis H shown as (+) moves through the enzyme, creating a whirling, which is energy to crunch ADP+P  ATP

THE DARK REACTION n Uses NADPH and ATP produced in the LIGHT REACTION to produce GLUCOSE n Requires 9 ATP for every 6 NADP n Short Movie Intro – Click ME Short Movie Intro – Click ME

The Dark Reaction is a Cycle

DA’ MAIN PLAYERS! n CO 2 is source of carbon (comes from the atmosphere) n RUBP is the 5 carbon starting point where C from CO 2 is inserted n Rubisco is the enzyme that helps produce glucose and keep the Dark Reaction going n PGA or phosphoglyceraldehyde (3C) is eventually glued together into glucose or becomes RUBP

What is the Result of the DARK REACTION (BESIDES BRAIN-PAIN FOR BIO 11 STUDENTS??) n Plant produces GLUCOSE molecules using the energy of ATP and NADPH n The Carbon came from CO2 gas from the atmosphere n Glucose = potential chemical energy is prodcuced, making plants the PRIMARY PRODUCERS 