bio 2.2

thylakoid membranes

light-dependent reactions of photosynthesis occur in the __ of chloroplasts and convert light energy into chemical energy in the form of ATP and NADPH

 Light Absorption

absorbed energy excites electrons within the photosystems to a higher energy state.

Photosystems

are complexes of proteins and pigments (like chlorophyll) embedded in the thylakoid membrane

 Electron Transport Chain

The energized electrons are transferred to a series of molecules. As the electrons move down, they release energy. (Will create high concentration of Hydrogen ions or H+)

Photolysis

To replace the electrons lost from Photosystem II, water molecules are split, releases oxygen as a byproduct, and the electrons are used to replenish the photosystem.

ATP and NADPH Formation

 The energy released from the electron transport chain is used to pump hydrogen ions into the thylakoid lumen, creating a proton gradient. Meanwhile, the electrons that have traveled down the chain are re-energized by light absorbed in Photosystem I and are then used to reduce NADP+ to NADPH

 ATP synthase

proton gradient drives the production of ATP through an enzyme called

Calvin cycle

The ATP and NADPH produced during these light dependent reactions are then used to power the

light-independent reactions

is a process used by plants and other photosynthetic organisms to convert carbon dioxide from the atmosphere into glucose

stroma

The Calvin cycle takes place in the __ of the chloroplasts

 Carbon Fixation

 The enzyme RuBisCO combines a molecule of carbon dioxide with a five-carbon sugar called ribulose-1,5-bisphosphate (RuBP). This creates an unstable six-carbon compound that immediately splits into two molecules of a three-carbon compound called 3-phosphoglycerate (3-PGA)

RuBisCO

this enzyme combines a molecule of carbon dioxide with a five-carbon sugar called ribulose-1,5-bisphosphate (RuBP).

ribulose-1,5-bisphosphate

RuBP

3-phosphoglycerate

3-PGA

Reduction

 3-PGA molecules are converted into a three-carbon sugar called glyceraldehyde-3-phosphate (G3P). This step uses energy from ATP and NADPH, which are produced during the light-dependent reactions of photosynthesis. Some of the G3P molecules are used to make glucose and other organic compounds.

glyceraldehyde-3-phosphate

G3P

Regeneration

The remaining G3P molecules are used to regenerate RuBP, the starting molecule for the cycle. This process requires more ATP to prepare the RuBP to accept more carbon dioxide and continue the cycle.

3

 turns of the Calvin cycle are needed to make one G3P molecule that can exit the cycle and go towards making glucose

3 turns of the Calvin cycle

3 RuBP

3 CO₂

3 RuBisCO

6 3-PGA

6 ATP

6 ADP

6 NADPH

6 NADP+

1 G3P

5 Recycled G3P

3 ADP

3 ATP