17.3 Light independent reaction Flashcards
What is another name for the light independent reaction?
Calvin cycle
Where does the light independent reaction take place?
In the stroma
Why is the Calvin cycle also called carbon dioxide fixation?
Because carbon from CO2 is fixed into an organic molecule.
What does the Calvin cycle make?
A molecule called triose phosphate from carbon dioxide and ribulose bisphosphate.
What can triose phosphate be used to make?
Glucose, glycerol, fatty acid and amino acids
What are the stages of the Calvin cycle?
1) Formation of glycerate 3-phosphate (GP)
2) Formation of triose phosphate (TP)
3) Regeneration of ribulose biphosphate
Describe the process of the Calvin Cycle.
1) Carbon dioxide enters the leaf through the stomata and diffuses into the stroma of the chloroplast.
2) Here it’s combined with ribulose biphosphate (RuBP), a 5-carbon compound and this gives an unstable 6-carbon compound which quickly breaks down into two molecules of a 3-carbon compound called glycerate 3-phosphate. Ribulose biphosphate carboxylase (RuBisCO) catalyses the reaction between carbon dioxide and RuBP.
3) The 3-carbon compound GP is reduced to a different 3-carbon compound called triose phosphate (TP) and ATP provides energy for this. The reaction also requires H+ ions which come from reduced NADP.
4) Reduced NADP is recycled to NADP.
5) Triose phosphate is then converted into many useful organic compounds.
6) Five out of every six molecules of TP are produced to regenerate RuBP. Regenerating RuBP uses the rest of the ATP produced by the light-dependent reaction.
What does carbon dioxide combine with to give an unstable 6-carbon compound?
Carbon dioxide combines with ribulose biphosphate (RuBP), a 5-carbon compound.
What does the unstable 6-carbon compound break down into?
It breaks down into two molecules of a 3-carbon compound called glycerate 3-phosphate (GP).
What enzyme catalyses the reaction between carbon dioxide and RuBP?
Ribulose biphosphate carboxylase (RuBisCO)
What is the 3-carbon compound GP reduced to?
Triose phosphate (TP)
How is one hexose sugar made?
By joining two molecules of triose phosphate (TP) together
How many times does the Calvin cycle need to turn to make one hexose sugar?
Six times BECAUSE -
- Three turns of the cycle produces six molecules of triose phosphate because two molecules of TP are made for every one CO2
- Five out of six of these TP molecules are used to regenerate ribulose biphosphate (RuBP) so for three turns of the cycle only one TP is produced to make a hexose sugar.
How many ATP does six turns of the cycle need?
18 ATP
How many reduced NADP does six turns of the cycle need?
12 reduced NADP
