Review of the calvin cycle, one carbon at a time

1. Calvin Cycle Better Explained

2. The original lecture had this diagram of the calvin cycle. An infographic in it’s own right, it
didn’t help convey information to students who weren’t already familiar with how the calvin
cycle worked.
I tried to break the Calvin Cycle into individual steps using color coded circles to represent
inorganic and fixed (organic) carbon molecules.
My slides are still fairly wordy, despite my efforts.
Expressing chemistry in pictures isn’t the kind of thing that happens overnight.
You know how “they” say you can’t make everyone happy? If I make jokes during class to
lighten the mood or break up the monotany of what is otherwise a very dense lecture, I get
comments about how I’m being disruptive to my own class in my course evaluations. I think
this goes back to my prior blog post about needing to make a companion blog to my class
where I explain “why we do what we do” for teaching.
I’m not making a photosynthesis joke just to be funny, I’m trying to keep a lecture hall of
students engaged. I’ve also found that if something has a powerful emotion tied to it, I’m more
likely to remember it – so laughter is the preferred emotion to evoke during lecture

3. Calvin Cycle

4. Circles represent atoms of Carbon

5. Circles represent atoms of Carbon
• Blue circles are inorganic carbon

6. Circles represent atoms of Carbon
• Blue circles are inorganic carbon
• Green circles are organic carbon

7. Circles represent atoms of Carbon
• Blue circles are inorganic carbon
• Green circles are organic carbon
• Inorganic molecules are not available to most biological organisms. Only
autotrophs can access inorganic carbon, like CO2
• Organic carbon, like sugar is available to heterotrophs and chemo-
organotrophs.
• Carbon fixation is the process by which autotrophs take inorganic carbon
and turn it into organic carbon
• The Calvin cycle is a way that autotrophs do carbon fixation

8. RuBP is made up of 5 organic carbons
RuBP CO2
Carbon Dioxide is made up of 1
inorganic carbon

9. Rubisco is the most abundant enzyme on earth
and it catalyzes a reaction whereby RuBP
combines with CO2 – a carboxylation reaction
RuBP CO2
The carbon from CO2 will now have green and
blue strips to indicate it just now got converted
from inorganic to organic carbon

10. Rubisco is the most abundant enzyme on earth
and it catalyzes a reaction whereby RuBP
combines with CO2 – a carboxylation reaction

11. Rubisco is the most abundant enzyme on earth
and it catalyzes a reaction whereby RuBP
combines with CO2 – a carboxylation reaction
RuBP CO2

12. Rubisco is the most abundant enzyme on earth
and it catalyzes a reaction whereby RuBP
combines with CO2 – a carboxylation reaction
RuBP CO2

13. The carboxylation reaction turns what was RuBP
and CO2, into an organic 6-carbon compound
The carbon from CO2 will now be green with a
blue outline to indicate it just now got
converted from inorganic to organic carbon
6-carbon compound

14. The 6-carbon compound is unstable and almost
immediately breaks down into 2, 3-carbon
compounds known as 3-phosphoglycerate or
3PGA for short
3PGA 3PGA

15. 3PGA itself is not that stable a molecule. For each 3PGA, a
molecule of ATP and a molecule of NADPH must be used to
convert each molecule of 3GPA into a molecule of trios, a 3
carbon sugar
Two molecules of ATP and
2 molecules of NADPH
Two molecules of
3PGA
+
+
=
= Two molecules of triose
phosphate

16. Even though we have made two molecules of trios phosphate,
we have only fixed one new carbon. The other 5 carbons were
part of RUBP.
Two molecules of ATP and
2 molecules of NADPH
Two molecules of
3PGA
+
+
=
= Two molecules of triose
phosphate

17. We have to regenerate RuBP. If we did so now, we would be
left with one carbon and we would basically be releasing it at
CO2
Two molecules of ATP and
2 molecules of NADPH
Two molecules of
3PGA
+
+
=
= Two molecules of triose
phosphate

18. Instead we have to go through the Calvin Cycle 3 times.
Two molecules of ATP and
2 molecules of NADPH
Two molecules of
3PGA
+
+
=
= Two molecules of triose
phosphate

19. The Calvin Cycle = The first time
Input
• 1 RuBP Molecule = 5 organic carbons
• 2 ATP Molecules
• 2 NADPH Molecules
Output
• 2 trios phosphates = 6 organic carbons
Total
Input
• 1 RuBP Molecule = 5 organic carbons
• 2 ATP Molecules
• 2 NADPH Molecules
Output
• 2 trios phosphates = 6 organic carbons
Round
1

20. The Calvin Cycle = The second time
Input
• 2 RuBP Molecule = 10 organic carbons
• 4 ATP Molecules
• 4 NADPH Molecules
Output
• 4 trios phosphates = 12 organic carbons
Total
Input
• 1 RuBP Molecule = 5 organic carbons
• 2 ATP Molecules
• 2 NADPH Molecules
Output
• 2 trios phosphates = 6 organic carbons
Round
1
Input
• 1 RuBP Molecule = 5 organic carbons
• 2 ATP Molecules
• 2 NADPH Molecules
Output
• 2 trios phosphates = 6 organic carbons
Round
2

21. The Calvin Cycle = The third time
Input
• 3 RuBP Molecule = 15 organic carbons
• 6 ATP Molecules
• 6 NADPH Molecules
Output
• 6 trios phosphates = 18 organic carbons
Total
Input
• 1 RuBP Molecule = 5 organic carbons
• 2 ATP Molecules
• 2 NADPH Molecules
Output
• 2 trios phosphates = 6 organic carbons
Round
1
Input
• 1 RuBP Molecule = 5 organic carbons
• 2 ATP Molecules
• 2 NADPH Molecules
Output
• 2 trios phosphates = 6 organic carbons
Round
2
Input
• 1 RuBP Molecule = 5 organic carbons
• 2 ATP Molecules
• 2 NADPH Molecules
Output
• 2 trios phosphates = 6 organic carbons
Round
3

22. Finally! When we get through the Calvin Cycle for the third
time, we have output more organic carbons than we have
input
Input
• 3 RuBP Molecule = 15 organic carbons
• 6 ATP Molecules
• 6 NADPH Molecules
Output
• 6 trios phosphates = 18 organic carbons
Total

23. Finally! When we get through the Calvin Cycle for the third
time, we have output more organic carbons than we have
input
Input
• 3 RuBP Molecule = 15 organic carbons
• 6 ATP Molecules
• 6 NADPH Molecules
Output
• 6 trios phosphates = 18 organic carbons
• BUT ONLY 3 of the 18 carbons were just
fixed. The other 15 are from our RuBP
investment
Total

24. Finally! When we get through the Calvin Cycle for the third
time, we have output more organic carbons than we have
input
Input
• 3 RuBP Molecule = 15 organic carbons
• 6 ATP Molecules
• 6 NADPH Molecules
Output
• 6 trios phosphates = 18 organic carbons
• BUT ONLY 3 of the 18 carbons were just
fixed. The other 15 are from our RuBP
investment
Total
Output – Input = Net

25. Finally! When we get through the Calvin Cycle for the third
time, we have output more organic carbons than we have
input
Input
• 3 RuBP Molecule = 15 organic carbons
• 6 ATP Molecules
• 6 NADPH Molecules
Output
• 6 trios phosphates = 18 organic carbons
• BUT ONLY 3 of the 18 carbons were just
fixed. The other 15 are from our RuBP
investment
Total
Output – Input = Net
18 carbons – 15 carbons = 3 carbons

26. Finally! When we get through the Calvin Cycle for the third
time, we have output more organic carbons than we have
input
Input
• 3 RuBP Molecule = 15 organic carbons
• 6 ATP Molecules
• 6 NADPH Molecules
Output
• 6 trios phosphates = 18 organic carbons
• BUT ONLY 3 of the 18 carbons were just
fixed. The other 15 are from our RuBP
investment
Total
Output – Input = Net
18 carbons – 15 carbons = 3 carbons
The net yield of three carbons is enough to produce 1 triosphate.

27. Finally! When we get through the Calvin Cycle for the third
time, we have output more organic carbons than we have
input
Input
• 3 RuBP Molecule = 15 organic carbons
• 6 ATP Molecules
• 6 NADPH Molecules
Output
• 6 trios phosphates = 18 organic carbons
• BUT ONLY 3 of the 18 carbons were just
fixed. The other 15 are from our RuBP
investment
Total
Output – Input = Net
18 carbons – 15 carbons = 3 carbons
The net yield of three carbons is enough to produce 1 triosphate.
In order to take the 15 invested organic carbons and transform them from trios
phosphates into RuBP an additional 3 ATP must be spent

28. Finally! When we get through the Calvin Cycle for the third
time, we have output more organic carbons than we have
input
Input
• 3 RuBP Molecule = 15 organic carbons
• 6 ATP Molecules
• 6 NADPH Molecules
Output
• 6 trios phosphates = 18 organic carbons
• BUT ONLY 3 of the 18 carbons were just
fixed. The other 15 are from our RuBP
investment
Total
Output – Input = Net
18 carbons – 15 carbons = 3 carbons
The net yield of three carbons is enough to produce 1 triosphate.
In order to take the 15 invested organic carbons and transform them from trios
phosphates into RuBP an additional 3 ATP must be spent
This means the production of 1 trios phosphate molecule costs 9 ATP