Process of Photosynthesis

(takes place inside the chloroplast)

8-3 pg. 235

PhotosystemsO Located in the Thylakoid; clusters of

chlorophyll and proteins.

Photosystem IIO Contains chlorophyll molecules that

absorb light. O When activated by light energy it

gives up electrons which are then absorbed by the electron acceptor.

O Electron accepter- part of an energy transfer system through which the electrons move until the reach photosystem I.

Electron Transport Chain

O Energy from the electrons is used by the proteins in the chain to pump H+ ions from the stroma into the thylakoid space. At the end of the electron transport chain, the electrons themselves pass to photosystem I.

ATP SynthaseO Membrane protein through which

excess hydrogen ions escape a thylakoid in a process that makes ATP.

Photosystem IO The electrons do not contain as much

energy as they used to. Pigments use energy from light to reenergize the electrons. At the end of a short electron transport chain, NADP+ molecules in the stroma pick up the high energy electrons, along with H+ ions, at the outer surface of the thylakoid membrane to become, NADPH

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Calvin Cycle (Light independent Reaction) O 3 phases

O FixationO ReductionO Regeneration

FixationO The cycle spends ATP as an energy

source and consumes NADPH as reducing power for adding high energy electrons to make the sugar. There are three phases of the cycle. In phase 1 (Carbon Fixation), CO2 is incorporated into a five-carbon sugar named ribulose bisphosphate (RuBP).

ribulose bisphosphate (RuBP).

O The enzyme which catalyzes this first step is RuBP carboxylase or rubisco. It is the most abundant protein in chloroplasts and probably the most abundant protein on Earth.

O The product of the reaction is a six-carbon intermediate which immediately splits in half to form two molecules of 3-phosphoglycerate.

ReductionO In phase 2 ( Reduction), ATP and

NADPH from the light reactions are used to convert 3-phosphoglycerate to glyceraldehyde 3-phosphate, the three-carbon carbohydrate precursor to glucose and other sugars.

RegenerationO In phase 3 (Regeneration), more

ATP is used to convert some of the of the pool of glyceraldehyde 3-phosphate back to RuBP, the acceptor for CO2, thereby completing the cycle..

RegenerationO For every three molecules of CO2

that enter the cycle, the net output is one molecule of glyceraldehyde 3-phosphate (G3P). For each G3P synthesized, the cycle spends nine molecules of ATP and six molecules of NADPH. The light reactions sustain the Calvin cycle by regenerating the ATP and NADPH.

Bottom Line of Calvin cycle

OBottom line is 3 CO2 from the atmosphere are converted to glyceraldehyde 3-phosphate (G3P) and ATP & NADPH from the light stage are used in the process.

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