Light-Independent Reactions

The Calvin Cycle

General Info

• A series of 11 reactios tha occur within the stroma of chloroplasts

  • Endergonic reaction - Uses Energy from ATP hydrolysis

  • Goal is to produce glucose~ used for cellular respiration

Rubisco

Most important enzyme in the biosphere

• Very Large and Slow Working enzyme

  • Only 3 reaction/second as ooposed to 1000/s compared to most enzymes

  • Therefore, plants need a large amount of Rubisco

    • on average half of all protein in plants

Phase 1: Carbon Fixation

• A Carbon dioxide enters through the stroma.

• Synthesis Reaction (Synthase)

  • CO2 is attached to 1,5-RuBP becomes a 6C molecule

• 6C molecule is split into two 3C molecules~ 3-PG

Phase 2 Reduction:

• ATP phosphorylates each 3-carbon molecule (PGA)

  • Enzyme:Kinase

  • Turns 3-PG into 1,3-BPG (bisphosphate glycerate)

• NADPH is used to produce G3P

  • Redox reaction

  • Enzyme: dehydrogenase

  • 1 phosphate relased

  • NADPH > NADP+

Phase 3: Regeneration of 1,5-RuBP

Of 6 G3p produced, one of them exits the cycle to eventually become glucose and other types of organic compounds

• Other G3P continue in cycle and help regenerate RuBP

  • 5 G3P and 3 ATP can produce 3 RuBP

Summary

Cycle occurs 6x to produce 1 glucose

• 2 G3P exits produces Glucose (gluconeogenesis)

Requirements:

• 9 ATP

  • 6 to turn 3-PGA into 1,3-BPG

  • 3 to regen 1,5-RuBP

• 6 NADPH

  • To reduce BPG and to remove a phosphate from each