Lecture 13- Light Independent reactions Flashcards
Where is the energy harvested in the light dependent reactions used?
In the light independent reactions.
What are the light independent reactions?
They are reactions that involve the fixation of carbons from CO2 to form organic carbohydrates.
What are the 3 steps of the light independent reactions and where do they take place?
The light independent reactions occur through the Calvin cycle in the chloroplast stroma. They are carbon fixation, reduction, and regeneration of RUBP.
What is the reaction for the light independent reactions?
6 CO2 + 18 ATP + 12 NADPH + 12 H2O –> C6H12O6 + 18 ADP + 18 P + 12 NADP+ 6 O2
What is the key intermiediate of the Calvin cycle? Where does it go?
Glyceraldehyde-3-Phosphate (G3P). Some of it stays in the cycle to regenerate RuBP, while other molecules escape to undergo reverse glycolysis to become glucose.
What are the two reaction catalyzed by rubisco? What type of relationship do they have?
They are the Calvin cycle and photorespiration, and they do competitive inhibition for Rubisco. Rubisco can bind the O2 to begin photorespiration, or the CO2 to begin the Calvin cycle.
What does photorespiration do?
It uses Oxygen, which is necessary to detoxify the plant, but it also gets rid of CO2, which is counterproductive.
What are the rates of carbon fixation vs photorespiration under normal conditions?
4:1, meaning 20% of the CO2 is misused.
What are the stomata? What can cause them to close?
They are pores by which CO2 diffuses into the leaves.
When temperatures are too high, the stomata close to conserve the water that is present inside the plant.
What are conditions that increase photorespiration?
High temperatures and high O2.
What are C3 plants?
They are plants which contain no mechanism to regulate photorespiration.
What are C4 plants?
They are plants which fix carbons from CO2 to PEP, which is then decarboxylated directly at the active site of Rubisco. This is done by two different cells, and ensures that CO2 concentration is higher than O2 concentration at the active site, even though the opposite might be true overall in the cell.
What are examples of C4 plants?
Corn, sugar cane, and grasses.
What are the two cells involved in the C4 Calvin cycle?
The Mesophyll cell, where CO2 is fixated to PEP, and the bundle sheath cells, where Calvin cycle occurs.
What is the drawback of C4 plants?
They must use ATP to fix CO2 to PEP.
