Photosynthesis Flashcards
(20 cards)
Light-dependent reaction produces….
NADPH, oxygen, ATP, H+
Light-independent reaction produces…
trisphosphate sugar, NADP, ADP
Calvin cycle
Light-independent reaction that converts carbon dioxide to triosephosphate
Cycles 6 times to make up one sugar
Steps in Calvin cycle (in order):
- Carboxylation
- Reduction
- Regeneration
In carboxylation, carbon dioxide is…
fixed through using rubisco (enzyme) and ribulose bisphosphate
The end product of carboxylation is an….
unstable 6C compound which immediately breaks into to two 3C compound (phosphoglycerate)
Glycerate-3-phosphate (phosphoglycerate) combines with (…) to make (…)
ATP and NADP, triose phosphate
Ribulose 1,5, bisphosphate can be remade through…
using ATP on the 5C of glycerate-3-phosphate to make 3 ribulose bisphosphate
Calvin cycle uses (…) ATP for the first time, (…) NADPH and (…) ATP for the last time in one cycle
6,6,3
Rubisco properties
Catalyses CO2 fixation
Available in the stroma
Can oxygenase
Rubisco’s fatal flaw is….
Oxygenation, fixing oxygen to become 2-phosphoglycolate
Photorespiration
When rubisco oxygenates, toxin is produced and needs to be detoxified
Photorespiration is bad because…
it produces toxins that needs to be detoxified (through peroxisome, mitochondria and chloroplast) hence expending more ATP and result more CO2
C2 Cycle is also called as…
oxidative photosynthetic carbon cycle, since photorespiration is abundant process
C2 vs C3
C2 - photorespiration, used for plants in extremely hot and dry environments, 2C
C3 - common 3C carbon fixation cycle. Calvin cycle
C4 photosynthesis have…
PEP (Phosphoenolpyruvate) carboxylase
Spatial segregation
What does PEP carboxylase do?
It only fixes carbon dioxide/bicarbonate so it combines CO2 to PEP (3C) to make a 4C compound (malate) then transfers it to low CO2 concentration (near chloroplast) area where malate decarboxylates. PEP carboxylase have a higher affinity to carbon dioxide than rubisco. Malate is then recycled back.
How does the segregation help concentrate the CO2 in one area?
The spatial segregation helps divide the concentration of CO2 between the two spaces. The top space is mesophyll cell and the bottom is bundle sheath cell, where Calvin cycle occurs. Mesophyll cell collects the CO2 using the PEP carboxylase.
How does C4 come about?
Due to the influx of photorespiration, photosynthesis and photorespiration are competing with each other
CAM (Crassulacean acid metabolism)
Have temporal segregation as stomata opens at night time to reduce water loss. Malate is stored in the vacuole and decarboxylated during the day
