calvin cycle review
TRANSCRIPT
Calvin Cycle Better Explained
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
Calvin Cycle
Circles represent atoms of Carbon
Circles represent atoms of Carbon• Blue circles are inorganic carbon
Circles represent atoms of Carbon• Blue circles are inorganic carbon
• Green circles are organic carbon
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
RuBP is made up of 5 organic carbons
RuBP CO2
Carbon Dioxide is made up of 1 inorganic carbon
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
Rubisco is the most abundant enzyme on earth and it catalyzes a reaction whereby RuBP combines with CO2 – a carboxylation reaction
Rubisco is the most abundant enzyme on earth and it catalyzes a reaction whereby RuBP combines with CO2 – a carboxylation reaction
RuBP CO2
Rubisco is the most abundant enzyme on earth and it catalyzes a reaction whereby RuBP combines with CO2 – a carboxylation reaction
RuBP CO2
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
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
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
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
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
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
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
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
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
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
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
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
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
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.
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
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