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Calvin Cycle: Light-Independent Reactions Explained

Aug 11, 2024

Light Independent Reaction (Calvin Cycle) Lecture Notes

Overview

  • Discusses continuation from the light-dependent reaction in photosynthesis.
  • Light-independent reaction also known as the Calvin Cycle.

Key Concepts

Purpose

  • Formation of organic molecules: Glucose, fructose, amino acids, phospholipids, and fatty acids.
  • Location: Takes place in the stroma of the chloroplast.

Terminology

  • Calvin Cycle: Another name for light-independent reaction.
  • Stroma: Space within the chloroplast where the Calvin Cycle occurs.

Process Details

Carbon Fixation

  1. Ribulose Bisphosphate (RuBP): 5-carbon molecule in stroma.
  2. Carbon Dioxide (CO2): Three molecules of CO2 are used.
  3. Carboxylation: CO2 is added to RuBP by enzyme Rubisco (Ribulose bisphosphate carboxylase).

Formation of 3-Carbon Molecules

  1. Unstable 6-Carbon Molecule: Formed by the addition of CO2 to RuBP, splits into two 3-carbon molecules called Glycerate Phosphate (GP) or Phosphoglycerate (PG).
  2. Reduction: GP or PG is reduced to form Triose Phosphate (TP).
    • Hydrogen Source: Provided by reduced NADP.
    • Energy Source: ATP is required.

Regeneration of RuBP

  1. Triose Phosphate (TP): Some TP is used to regenerate RuBP, requiring ATP.
  2. Excess TP: Used to form various organic molecules.

Exam Essentials

  1. Carboxylation of RuBP: Forms an unstable 6-carbon compound, catalyzed by Rubisco.
  2. Reduction of GP/PG: Uses ATP and reduced NADP to form TP.
  3. Regeneration of RuBP: Uses ATP; excess TP forms organic molecules.

Organic Molecule Formation

  • Hexose Sugars: Glucose, fructose, formed from TP.
  • Cellulose: From beta-glucose, part of plant cell wall.
  • Sucrose: For translocation through the phloem.
  • Starch: For energy storage.
  • Amino Acids: Formed by adding ammonium or nitrate to TP.
  • Fatty Acids and Glycerol: Direct conversion from GP/PG to form phospholipids and triglycerides.

Important Points

  • Rubisco: Most common enzyme in the world, present in all photosynthetic organisms.
  • Energy Requirements: Both ATP and reduced NADP are essential for the Calvin Cycle.
  • Flexibility: Calvin Cycle produces a variety of organic molecules crucial for plant structure and metabolism.

Summary

  • Calvin Cycle is integral for forming organic molecules necessary for plant life.
  • The process relies on energy and reducing power from the light-dependent reactions.
  • Understanding the steps and enzymes involved is crucial for exam success.

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