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Photosynthesis Poster
3
The Processes of Photosynthesis
By: Thomas Wu and Om Bhagia
Photosynthesis
Sunlight is absorbed by the chloroplasts of the cell. The sun is the source of energy in photosynthesis
Photosynthesis
Sunlight
Chloroplast
Light
Reflected Light
Stroma
Chloroplast
Granum
Thylakoid Lumen
Thylakoid Membrane
Lamellae
Thylakoid
Stroma
Sunlight
H+
NADP+ + -> NADPH
H+
ADP -> ATP
Plastocyanin
Cytochrone Complex
ATP Synthase
2 e-
Thylakoid membrane
H+
Re-excited electrons
De-energized electrons
A pair of excited electrons
H+ gradient established
Thylakoid Membrane
Thylakoid Lumen
2 excited electrons for the ETC
Photosystem II absorbs a photon - this causes photoactivation and excites two electrons, propelling them into the ETC. Electrons are replenished through photolysis.
Reaction centre
Photon
Photosystem II
Antenna pigments
Photolysis
+
4e-
O2(g)
Energy
4H+
+
2
Photolysis
Photolysis: energy is needed to break the bonds of the water molecules - this energy comes from the sunlight the chlorophyll has been absorbing. The excess products of the reaction are hydrogen ions (protons) and oxygen gas. Oxygen gas is often excreted as waste, while hydrogen ions will serve as an important part of a later process of photosynthesis.
Stairs analogy: as the two energized electrons travel throughout the electron transport chain, they lose energy - losing energy each step down.
Topic
The released energy from the electrons allow for Hydrogen ions to pass through the thylakoid membrane, establishing the electrochemical gradient.
2 re-excited electrons for the formation of NADPH
Photosystem I takes energy depleted electrons from the ETC and re-energizes them through photoactivation. The electrons are used to reduce NADP+ to NADPH, an important compound for the Calvin cycle later on.
Reaction centre
Photon
Photosystem I
Antenna pigments
Electrons from ETC
ADP -> ATP
ATP Synthase
The electrochemical gradient allows for chemiosmosis across the ATP synthase channel. The high energy protons rushing through the channel provide ample energy for ADP to reduce into ATP
H+
Stroma
carbon dioxide
Stomata
stroma
The Calvin Cycle
2 carbon dioxide
ribulose 1,5-bisphospate
unstable 6C molecule
Carbon Fixing
3-phosphoglycerate
ribulose 5-phosphate
Regeneration of RuBP
Reduction
2 ATP become 2 ADP + phosphate
1,3-bisphosphoglycerate
glyceraldehyde-3-phosphate
ribulose bisphosphate (5 carbon molecule) + carbon dioxide
unstable 6C molecule
(RuBP)
enzyme is ribulose bisphosphate carboxylase
breaks down
2 molecules of 3-phosphoglycerate (each has 3 carbons)
also known as PGA
2 PGA molecules, each phosphorylated into 1,3-bisphosphoglycerate by ATP
thus, 2 ATP used per carbon dioxide
2 NADPH are oxidized in reducing 2 (1,3-bisphosphoglycerate) to 2( glyceraldehyde-3-phosphate)
water also produced
purposes of glyceraldehyde-3-phosphate (G3P)
- provide chemical energy in the cell
- combine to form glucose
- recycled and combined to form RuBP
It takes 5 G3P to make 1 RuBP, but only one carbon can be used at a time to make glucose
takes 6 turns of the Calvin Cycle per glucose molecule
The production of 1 glucose needs
- 12 PGA
- 12 1,3-bisphosphoglycerate
- 18 ATP
- 12 NADPH