Biochemistry - Calvin Cycle Question

In summary, when the light is suddenly switched off in an illuminated suspension of chloroplasts actively carrying out photosynthesis, the levels of 3-phosphoglycerate would actually increase instead of decrease. This is because while the production of Ribulose 1,5-Bisphosphate would be affected by the absence of ATP and NADPH, the reactions that produce 3-PG do not require these compounds. Therefore, carbon fixation would still occur, leading to an increase in 3-PG levels.
  • #1
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Homework Statement



An illuminated suspension of chloroplasts is actively carrying out photosynthesis. What would happen to the levels of 3-phosphoglycerate and Ribulose 1,5-Bisphosphate if the light was suddenly switched off?


Homework Equations





The Attempt at a Solution



I thought that the answer would be that the levels of 3-phosphoglycerate and Ribulose 1,5-Bisphosphate would decrease because the CO2 that is fed into the Calvin Cycle to make these compounds comes from the light-dependent reactions. Also, 3 of the enzymes in the stroma that regulate the Calvin Cycle are light-dependent as well.

However, someone told me that the 3-phosphoglycerate levels would increase instead. I was wondering if someone could please tell me why this would happen?

Thanks in advance!
 
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  • #2
persephone said:
the CO2 that is fed into the Calvin Cycle to make these compounds comes from the light-dependent reactions.

This statement is incorrect. There are two important molecules that are produced by the light-dependent reactions. What are they and how might removing them affect the Calvin cycle?
 
  • #3
Ygggdrasil said:
This statement is incorrect. There are two important molecules that are produced by the light-dependent reactions. What are they and how might removing them affect the Calvin cycle?

Sorry, I don't know why I said that. The molecules that are produced by the light-dependent reactions are ATP and NADPH. I know that you need both to make Ribulose 1,5-Bisphosphate in the Calvin Cycle, so that means shutting off the light would decrease the levels of Ribulose 1,5-Bisphosphate.

However, ATP and NADPH are NOT needed to make 3-Phosphoglycerate. So I am still not sure how shutting off the lights would effect the levels of this compound...If you could please clarify this for me I would really appreciate it!
 
  • #4
Think of the reactions that produce 3-PG and those that use up 3-PG. Which reactions are dependent on ATP and NADPH and which ones do not require these compounds?
 
  • #5
had a question like this on bio exam. Remember that Carbon fixation is still occurring but the rest of the cycle is not.
 

1. What is the Calvin Cycle?

The Calvin Cycle is a series of biochemical reactions that occur in the chloroplasts of plant cells. It is responsible for the conversion of carbon dioxide and water into glucose, using energy from sunlight.

2. What is the role of carbon dioxide in the Calvin Cycle?

Carbon dioxide is a key component in the Calvin Cycle, as it is the source of carbon for the production of glucose. It is taken in from the atmosphere and combined with other molecules to form glucose during the cycle.

3. How does the Calvin Cycle use energy from sunlight?

The Calvin Cycle uses energy from sunlight through a process called photosynthesis. Specifically, the energy is captured by pigments in the chloroplasts, such as chlorophyll, and is used to power the biochemical reactions that occur during the cycle.

4. What are the products of the Calvin Cycle?

The products of the Calvin Cycle are glucose, which is used as a source of energy for the plant, and oxygen, which is released into the atmosphere as a byproduct of the photosynthesis process.

5. How does the Calvin Cycle contribute to the overall functioning of a plant?

The Calvin Cycle is essential for the survival of plants, as it is responsible for producing glucose, which is used as a source of energy for all cellular processes. Additionally, the oxygen produced during the cycle is necessary for respiration, which allows plants to convert glucose into usable energy.

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