Calvin Cycle Flashcards
The cycle was discovered by ________ , ________ & ________ at the University of California, Berkeley
Melvin Calvin, Andrew Benson, and James Bassham
By using a radioactive isotope carbon-14 to trace the path of carbon atoms in carbon fixation, they performed experiments in unicellular algae Chlorella.
Second stage of photosynthesis that is involved in the formation of sugar from CO2 using chemical energy stored
THE CALVIN CYCLE
light-independent reactions or “dark reactions” or reductive phosphate cycle.
The Calvin Cycle needs to ‘spin’ (how many times) to make one molecule of G3P from three molecules of CO2
3
What is a process of incorporating an inorganic carbon molecule, CO2, into an organic molecule?
CARBON FIXATION
CO2 molecule is attached to a five-carbon sugar molecule named Ribulose-1,5- bisphosphate (RuBP) aided by an enzyme named ________?
Ribulose- 1, 5- bisphosphate carboxylase/oxygenase
(Rubisco)
Carbon Fixation
Ribulose- 1, 5- bisphosphate must
first be phosphorylated by the enzyme
Phosphoribulose kinase
Carbon Fixation
What is believed to be the most abundant protein in the chloroplast and maybe on Earth?
Ribulose- 1, 5- bisphosphate carboxylase/oxygenase
(Rubisco)
The resulting product, a six-carbon sugar, is extremely unstable and immediately splits into half. The split forms two molecules of ____?
3-phosphoglycerate
(3-carbon), Carbon Fixation
A phosphate group (from ATP) is then attached to each 3-phosphoglycerate by an enzyme _________ forming 1,3-Biphosphoglycerate.
Phosphoglycerate kinase (PGK)
Reduction
Next, 1-3 Biphosphoglycerate is reduced by (1) to yield NADP+ and Glyceraldehyde-3-phosphate (G3P) with the aid of (2)
(1) NADPH, (2) Glyceraldehyde-3-phosphate dehydrogenase
Reduction
For every six G3Ps produced by the Calvin Cycle, ____ are recycled to regenerate 3 molecules of RuBP
(NUMBER)
5
Only _ G3P leaves the cycle to be
packaged for use by the cell.
(NUMBER)
1
It will take _ molecules of G3P to make one molecule of glucose
2
Glyceraldehyde-3-phosphate (G3P) is then reversibly converted to Dihydroxyacetone phosphate (DHAP) by ______ .
Triosephosphate Isomerase (TIM)
(1.4)
________ condenses the two DHAP molecules to form Fructose- 1,6 bisphosphate (FBPase)
Aldolase
(1.5)
CONVERTS
Fructose-1, 6-bisphosphate -> F6P (Fructose-6-Phosphate)
FBPase (Fructose 1, 6-Bisphosphatase)
(1.6)
Dihydroxyacetone phosphate (DHAP) is converted in fructose-6-phosphate (F6P)
by ________?
CONVERTS DHAP in F6P
Aldolase and Fructose biphosphatase
(1.6.1) Converts DHAP in F6P
Fructose 6-phosphate can then be converted into glucose via two enzymatic steps with the help of ________?
Phosphoglucoisomerase and Glucose-6-Phosphatase
(1.6.2) F6P -> C6H12O6
F6P has two carbons removed by ________ giving Erythrose-4-phosphate (E4P)
Transketolase
(1.7)
The two carbons on ________ are added to a G3P giving the Xylulose-5-Phosphate (X5P)
Transketolase
(1.7)
Dihydroxyacetone (DHA) can also go on to condense with Erythrose-4-phosphate (E4P) to form Sedoheptulose-1, 7-biphosphate (SBP). This reaction is catalysed by ______.
Aldolase
(1.8)
Sedoheptulose-1, 7-biphosphate (SBP). is then de-phosphorylated by ________ to yield Sedoheptulose-7-phosphate (S7P)
Sedoheptulose biphosphatase
(1.9)
After several rearrangement reactions utilizing ________ & ________, Xylulose-5-phosphate (X5P) and Ribose-5-phosphate (R5P) are synthesized.
Transketolase and Transaldolase
(1.10)
X5P is converted into Ribulose-5-phosphate (Ru5P) by______.
Phosphopentose epimerase
(1.11)
R5P is isomerized by ________ to yield Ribulose-5-phosphate (Ru5P)
Phosphopentose isomerase
(1.12)
Finally, ________ phosphorylates Ru5P, into RuBP, ribulose-1,5 bisphosphate
Phosphoribulose kinase
(1.13)
Recipe for CARBOHYDRATE
or to make one molecule of G3P
(3) CO2
(9) ATP
(6) NADPH
Recipe for GLUCOSE
(6) CO2
(18) ATP
(12) NADPH
Plants in which the Calvin cycle uses CO2 directly from the air are called ________?
C3 Plants
Examples of C3 Plants
soybeans, oats, wheat and rice
________ is an adaptation that reduces water loss, but it also prevents CO2 from entering the leaf and O2 from leaving.
Closing stomata
The entire process, starting with the fixation
of O2, is called ________?
photorespiration
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 defences.
________ have special adaptations that save water and also prevents photorespiration.
(moves CO2 molecules)
C4 plants
An enzyme fixes carbon into a four-carbon (4-C) compound instead of 3-PGA.
Phosphoenolpyruvate carboxylase (PEP carboxylase)
Examples of C4 Plants
Corn, sorghum, and sugar cane
______ conserves water by opening its stomata and admitting CO2 only at night.
Crassulacean Acid Metabolism (CAM) Plants
Examples of CAM Plants
Pineapples and Cacti
