The Calvin Cycle Flashcards
Calvin cycle involves
11 enzyme catalyst reactions that use NADPH to reduce CO2 to glucose through 3 turns. Endergonic
Calvin cycle reaction
1 CO2—1C6H12O6
After 3 turns
A G3P molecule is produced. 2 of these are needed to make one glucose
3 phases
They each happen during every turn. Fixation, reduction, and regeneration
Fixation
A carbon from CO2 is fixed to ribulose 1,5 biphosphate (RuBP) to produce 2 3 carbon 3 phosphoglycerate
Reduction
3-Phosphate glyceride gets a p from ATP becoming ADP producing 1, 3 Biphosphate glyceride. Sodium electrons from NADPH reduces them to G3P
Regeneration
A multistep process where 5 carbons rearrange to from RuBP
In 3 turns
3 CO2 + 3 RuBP— 6 3phosphoglyerides using 6 ATP.
Next step in 3 turns
6NADPH + 1, 3 phosphoglycerate— 6G3P molecules. Using ATP 5 G3P are turned into 3 RuBP
Overall
One extra G3P is produced and 9 ATP and 6 NADPH were used
Monosaccharides next steps
Becomes a disaccharide like sucrose or a polysaccharide like starch or cellulose , or consume G3P and change
Things G3P can become
Amino acids, fatty acids, lipids in the cytoplasm or cytosol
Sucrose
Glucose linked to fructose. Most common product to circulate from cell to cell. Stores organic molecules
RuBP
Most common protein on earth making up 50% of plant protein. Catalyzes the fixation of CO2.
Rubisco
A very slow enzyme
Rubisco shape
Cube with 8 small and 8 large sub units
Large subunits
Active site with defined bonding sites for CO2 and RuBP
Small subunit
Regulatory by not a catalyst
Rubisco synthesis
Uses genes from 2 different genomes. Large subunit encoded in the chloroplast and the small encoded in the cytosol, and then imported to the chloroplast for unification
Why is rubisco slow?
It is not only an enzyme for CO2, but also photo respiration
Photorespiration
Oxygen bonds with rubisco and a 2 carbon compound from the cytoplasm is made into CO2 using ATP
Rubisco evolution
Long time ago because many bacteria and archaea have them
Why does rubisco accept oxygen
In its evolutionary phase there was little oxygen present therefore it was not a problem the enzyme needs to fix
Oxygen and rubisco
A competitive inhibitor in a process called oxygenase
Oxygenase
Results in 1, phosphoglycerate and 1, 2 carbon phosphoglycolate. No carbon gain
Phosphoglycolate
Cant be processed by cells. When it is broken down by cells toxic glycolate is produced and takes carbon with it as it is expelled
Rubisco in the lab
In equal parts has a higher affinity for CO2, but in the real world there is much more oxygen that CO2 in the air.
Rubisco reaction rates
1/4 is oxidation, 3/4 is carboxylation
Carbon-concentrating mechanisms
In algae because water doesn’t have enough CO2
Carbon-concentrating mechanisms function
It pumps inorganic carbon in keeping the concentration in the cell high
Bicarbonate
Most used carbon in water plants. Pumped into the cytosol to become CO2 by an ATP dependent transported on the plasma membrane. CO2 then diffuses to the rubisco site to keep the concentration high
2 problems of land plants
Photorespiration and water loss. They are connected
Stomata
Holes in the plant leaves to allow for gas exchange. The diffusion determines the direction of CO2 in or )2 and H2O out
Stomata regulation
Done by the plants when they need, and nothing more
Why is oxidation worse in heat
All gas concentration decreases in heat but CO2 more rapidly. Therefore there is more oxygen bonding to the rubisco
C4 cycle
A second carbon fixation pathway to reduce photorespiration
C4 cycle process
CO2 and 3 carbon PEP — oxaloacetate– malate– transportation to the Calvin cycle– oxidation– pyruvate and CO2— PEP
Oxaloacetate
First product of C4. A 4 carbon chain
C3 vs C4
Distinguishes plants with or without the C4 cycle
Key distinction C3 and C4
Carboxylation reaction. C4 uses PEP carboxylase which is faster and can’t accept oxygen
C4 location
The mesophyll cells (the ones near the surface of the plant
Malate movement
Into the bundle sheath cells (not exposed to oxygen) where the calvin cycle makes them pyruvate and CO2
Why don’t all plants use C4
Every cycle uses 1 more ATP, it is good in the heat because there is lots of light and ATP with low CO2. But in colder climates it is worse
Why is C4 better for dry climates
In C3 the stroma had to stay open longer losing water
CAM plants
Crassulaceae acid metabolism. Plants switch between C3 and C4 reaction
CAM at night
Stomata’s open to release oxygen and bring in CO2, C4 works to make malate, and pyruvate is turned back into malate
In the day CAM
Stamata’s close, malate diffuses and is oxdized to pyruvate molecules, the Calvin cycle occurs
Plants
Photosynthesis in ones with chloroplast, cellular respiration happens in them all.
Photosynthesis vs cellular respiration
Opposite products vs reactants, both involve an ETC and G3P
