8.3 The Calvin cycle makes sugar from carbon dioxide Katrina Garibotto

Objectives Explain how the Calvin cycle makes sugar. Summarize the overall process of photosynthesis.

A trip around the calvin cycle “sugar factory” Starting material regenerated each time the cycle goes round Inputs: carbon dioxide, ATP, NADPH (the latter two come from the light reactions) Output: sugar (G3P, which is eventually used to make glucose)

A trip around the calvin cycle 3 CO2 and 3 RuBP molecules are connected by an enzyme, The newly-created molecules are unstable, so they immediately break in half, leaving 6 molecules. The new molecules are called 3-PGA. ATP (energy) and NADPH from the light reactions help turn the 3-PGA into G3P, a sugar that will eventually be converted into glucose. One molecule of G3P leaves and is used by plant cells. Five G3P molecules remain in the cycle. ATP provides energy for the remaining G3P molecules to be rearranged into RuBP so the cycle can continue. ADP and NADP+ go back to the light reactions.

Summary of photosynthesis Many complicated steps Big picture: 6 CO2 + 6 H2O + energy from sunlight → C6H12O6 + 6 O2 This is the first step in the flow of energy through almost every ecosystem. The oxygen you breathe comes from photosynthesis. The energy your body uses for fuel comes from photosynthesis. Isn’t life amazing?