Calvin Cycle Flashcards
Proponents of the Calvin-Benson-Bassam Cycle
- Melvin Calvin
- Andrew Benson
- James Bassam
Other names of the Calvin Cycle
- Light-Independent Reactions
- Dark Reactions
- Reductive Phosphate Cycle
Where does the Calvin Cycle take place?
Stroma of the Chloroplast
What is the Calvin Cycle?
It is the second stage of photosynthesis that is involved in the formation of sugar from CO2 using chemical energy stored
How many times does the Calvin Cycle need to “spin” in order to produce 1 molecule of G3P and 3 molecules of CO2
3
Three Phases of the Calvin Cycle
- Carbon Fixation
- Reduction
- Regeneration
What is Carbon Fixation?
Carbon fixation is a process of incorporating an inorganic carbon molecule, CO2, into an organic molecule.
CO2 molecule is attached to a five-carbon sugar molecule named Ribulose-1,5- bisphosphate (RuBP) aided by an enzyme named?
Rubisco or RuBP carboxylase/oxygenase.
In Reduction, Ribulose- 1, 5- bisphosphate must first be phosphorylated by what enzyme?
Phosphoribulose kinase
What is the most abundant protein in the chloroplast?
Rubisco
What is Carbon Fixation’s resulting product?
A six-carbon sugar
Additional Information: It is extremely unstable and immediately splits into half. The split forms two molecules of a 3-phosphoglycerate (3-carbon).
1-3 Biphosphoglycerate is reduced by NADPH to yield NADP+ and Glyceraldehyde-3-phosphate with the aid of?
Glyceraldehyde-3-phosphate dehydrogenase
For every six G3Ps produced by the Calvin Cycle, how many are recycled to regenerate three molecules of RuBP?
5
How many molecules of G3P is used to make 1 molecule of glucose?
2
Glyceraldehyde-3-phosphate is reversibly converted to Dihydroxyacetone phosphate by?
Triose phosphate isomerase
What enzyme condenses the two DHAP molecules to form Fructose-1,6 bisphosphate?
Aldolase
Dihydroxyacetone phosphate (DHAP) is converted in fructose-6-phosphate (F6P) by?
Aldolase and Fructose biphosphatase
Fructose 6-phosphate can then be converted into glucose via two enzymatic steps with the help of?
Phosphoglucoisomerase and Glucose-6-Phosphatase
F6P has two carbons removed by what enzyme in order to give Erythrose-4-phosphate?
Transketolase
The two carbons on what enzyme are added to a G3P giving the ketose Xylulose-5-Phosphate?
Transketolase
Dihydroxyacetone can also go on to condense with Erythrose-4-phosphate to form Sedoheptulose-1, 7-biphosphate (SBP). This reaction is catalyzed by what enzyme?
Aldolase
SBP is de-phosphorylated by what enzyme to yield Sedoheptulose-7-phosphate (S7P)?
Sedoheptulose biphosphatase
Xylulose-5-phosphate (X5P) and Ribose-5-phosphate (R5P) are synthesized after several rearrangement reactions utilizing what enzymes?
Transketolase and Transaldolase
X5P is converted into Ribulose-5-phosphate (Ru5P) by?
Phosphopentose epimerase
R5P is isomerized by what enzyme in order to isomerase to yield Ribulose-5-phosphate (Ru5P)?
Phosphopentose isomerase
What enzyme phosphorylates Ru5P, into RuBP, ribulose-1,5 bisphosphate?
Phosphoribulose kinase
What happens to G3P after its release from the cycle?
- 2 G3Ps can combine together to form either glucose or fructose which are both six-carbon sugar
- Glucose and fructose can be combined to form sucrose
- Glucose can be connected in chains to form starch
- G3Ps can also be used in lipid and protein synthesis
To make one molecule of G3P, the chloroplast needs?
3 molecules of CO2, 9 molecules of ATP, and 6 molecules of NADPH
To synthesize one glucose molecule, the Calvin cycle uses _______ molecules of CO2, _________ molecules of ATP, and _________
molecules of NADPH
6, 8, 12
Examples of C3 Plants
Soybeans, Oats, Wheat and Rice
The entire process, starting with the fixation of O2, is called?
Photorespiration
Photorespiration does not produce?
ATP
Advantages of Photorespiration
- Photorespiration can have photoprotective effects (preventing light-induced damaged to the molecules involved in photosynthesis
- Help maintain redox balance in cells
- Support plant immune defenses
Difference of C3 and C4 plants?
C4 plants have special adaptations that save water and also prevents photorespiration while C3 plants do not.
What special enzyme do C4 Plants contain?
Phosphoenolpyruvate carboxylase (PEP carboxylase)
What can Rubisco do that PEP carboxylase can not do?
PEP carboxylase, unlike rubisco in C3 plants cannot switch over to fixing O2
Examples of C4 Plants
Corn, sorghum, and sugar cane
CAM stands for?
Crassulaccean Acid Metabolism
Examples of CAM plants
Pineapples, many cacti and most of the so called succulent plants (those with very juicy tissues)
How does a CAM plant conserve water?
It conserves water by opening its stomata and admitting CO2 only at night
