6 turns of the Calvin Cycle produce a glucose molecule. But how many molecules of triose phosphate are produced?

The Calvin Cycle is a series of biochemical reactions that take place in the stroma of chloroplasts in photosynthetic organisms. It is also known as the light-independent reactions or the dark reactions.

Here's a step-by-step breakdown of the Calvin Cycle:

1. Carbon Fixation: The enzyme RuBisCO catalyzes the reaction between CO2 and a five-carbon sugar called ribulose bisphosphate (RuBP). This reaction produces a six-carbon compound that immediately splits into two molecules of 3-phosphoglycerate (3-PGA), a three-carbon compound.

2. Reduction: Each 3-PGA molecule is phosphorylated by ATP and reduced by NADPH to form glyceraldehyde 3-phosphate (G3P), also known as triose phosphate. This step uses up 2 molecules of ATP and 2 molecules of NADPH for each CO2 fixed.

3. Regeneration: Some of the G3P molecules are used to regenerate RuBP so that the cycle can continue. This step uses up 1 molecule of ATP for each CO2 fixed.

In each turn of the Calvin Cycle, one molecule of CO2 is fixed, and for every 3 turns, one molecule of G3P (triose phosphate) is produced. This is because 5 out of 6 molecules of G3P produced in 3 turns are used to regenerate RuBP, leaving only 1 G3P molecule as the net output.

Therefore, to produce one molecule of glucose (which has 6 carbons), the Calvin Cycle needs to turn 6 times, fixing 6 molecules of CO2. This would produce 2 molecules of G3P (since glucose is a six-carbon sugar and each G3P has 3 carbons).

However, the question asks how many molecules of triose phosphate are produced in 6 turns of the Calvin Cycle, not how many are left after RuBP regeneration. In each turn of the cycle, for each CO2 fixed, 2 molecules of G3P are produced. Therefore, in 6 turns of the Calvin Cycle, 12 molecules of G3P (triose phosphate) are produced.