Amount of ATP required in photosynthesis.

In summary, during the process of photosynthesis, three molecules of ATP and two molecules of NADPH are consumed for each CO2 molecule that is fixed. Each turn of the light independent cycle (Calvin-Benson) requires one CO2, three ATP, and two NADPH, and it needs six turns of the cycle to make one molecule of glucose. The light reaction of photosynthesis produces 18 ATP molecules and 12 NADPH molecules, which are used in the dark reaction to produce glucose. Aerobic respiration, on the other hand, needs two ATP molecules to start reactions and has a net yield of 36 ATP molecules.
  • #1
wasteofo2
478
2
Does anyone know how many ATP molecules are used in the process of photosynthesis? I think with aerobic respiration 2 are used, but I could be wrong.
 
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  • #2
ATP required in photosynthesis? ATP is produced during photosynthesis, so I guess you are referring to the carbon-fixation cycle?

Three molecules of ATP and two molecules of NADPH are consumed for each CO2 molecule that is fixed.
 
  • #3
So how much ATP and NADPH is produced out of every quantum of light?
 
  • #4
I seem to recall that 11 photons are required for one sugar molecule, which is later used by the cell to make other molecules. The point of what I was reading was that 3 photons would be 100% thermodynamic efficiency, so the actual process is a little under 30% efficient. This was long ago (~20 years) so maybe understanding has changed.
 
  • #5
Yes, my answer was incomplete, since the net reaction of carbon-fixation is:

[itex]3CO_2+9ATP+6NADPH+H_2O\rightarrow[/itex]
[itex]glyceraldehyde3phosphate+8P_i+9ADP+6NADP^+[/itex]

So this glyceraldehyde then can be the substrate for glucose prodcution.
 
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  • #6
Each turn of the light independent cycle (calvin-benson) requires 1 CO2, 3 ATP, and 2 NADPH. It needs 6 turns of the cycle to make 1 molecule of glucose because glucose has a 6 carbon atom backbone.

Aerobic respiration needs 2 ATP to start reactions and when completed will have a net yield of 36 ATP
 
  • #7
Originally posted by fish
Each turn of the light independent cycle (calvin-benson) requires 1 CO2, 3 ATP, and 2 NADPH. It needs 6 turns of the cycle to make 1 molecule of glucose because glucose has a 6 carbon atom backbone.

Aerobic respiration needs 2 ATP to start reactions and when completed will have a net yield of 36 ATP
You are partially right, I think.

This reaction takes place in the chloroplast:
[itex]3CO_2+9ATP+6NADPH+H_2O\rightarrow[/itex]
[itex]glyceraldehyde3phosphate+8P_i+9ADP+6NADP^+[/itex]

After which the glyceraldehyde 3-phosphate is exported into the cytosol, where it can be converted into fructose 6-phosphate and glucose 1-phosphate. The glucose 1-phosphate is then converted to the sugar nucleotide UDP-glycose, and this combines with the fructose 6-phosphate to form sucrose phosphate, the immediate precursor of the disaccharide sucrose (which the plant uses for energy).

I am not sure how much ATP is required to go from glyceraldehyde 3-phosphate to glycose 1-phosphate.
 
  • #8
Monique, you over complicated the question a bit. Firstly, photosynthesis doesn't make ATP, it makes [itex]C_6H_1_2O_6[/itex]

I wanted to know how many ATP molecules are used in the overall reaction of photosynthesis.

[itex]12H_2O+6CO_2+Light Energy\rightarrow
C_6H_1_2O_6+6O_2+6H_2O[/itex]

I thought that

[itex]C_6H_1_2O_6+6O_2\rightarrow
36ATP+6CO_2+6H_2O[/itex]

Used 2 molecules of ATP in the process...
 
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  • #9
Ok, but photosynthesis occurs in discrete steps, I was considering those. What you are giving is a net reaction, there are intermediate steps.

6 CO2 + 18 ATP + 12 NADPH = C6H12O6 + 18 (ADP + Pi) + 12 NADP+

There you go: the dark reaction of photosynthesis :)
 
  • #10
The light reaction takes 6 H2O and turns it into 6 O2.
12 NADP+ gets reduced to 12 NADPH and H+ during the reaction.

The H+ gradient is used to make 18 ATPs, which go into the dark reaction.
 
  • #11
Alright, 18 ATP moledules per glucose molecule, thanks.
 

1. How much ATP is required for photosynthesis to occur?

The exact amount of ATP required for photosynthesis varies depending on the specific conditions and factors involved. However, on average, one molecule of ATP is needed for every three molecules of carbon dioxide that are converted into sugar during the light-independent reactions of photosynthesis.

2. What role does ATP play in photosynthesis?

ATP (adenosine triphosphate) is a vital energy-carrying molecule that provides the necessary energy for the light-dependent and light-independent reactions of photosynthesis to occur. It is produced during the light-dependent reactions and is then used in the light-independent reactions to power the conversion of carbon dioxide into glucose.

3. How is ATP produced during photosynthesis?

ATP is produced during the light-dependent reactions of photosynthesis through a process called photophosphorylation. This involves the absorption of light energy by photosynthetic pigments, which is then used to power the production of ATP from ADP (adenosine diphosphate) and inorganic phosphate.

4. Can photosynthesis occur without ATP?

No, photosynthesis cannot occur without ATP. ATP is the primary source of energy that drives the chemical reactions involved in photosynthesis. Without ATP, the light-dependent and light-independent reactions would not have the necessary energy to take place, and photosynthesis would not occur.

5. How does the amount of ATP required for photosynthesis relate to the amount of light available?

The amount of ATP required for photosynthesis is directly related to the amount of light available. This is because the light-dependent reactions, which produce ATP, require light energy to occur. Therefore, the more light available, the more ATP can be produced, and the more photosynthesis can occur.

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