The Calvin Cycle: A Key Process in Photosynthesis
Concept Map
The Calvin cycle is a vital part of photosynthesis, occurring in the stroma of chloroplasts, where it transforms atmospheric CO2 into glucose. This light-independent process relies on ATP and NADPH from the light-dependent reactions and goes through phases of carbon fixation, reduction, and RuBP regeneration. Understanding this cycle is crucial for grasping how plants produce organic compounds, supporting life on Earth.
Summary
Outline
Exploring the Calvin Cycle: The Light-Independent Phase of Photosynthesis
Photosynthesis is a critical process through which plants, algae, and certain bacteria convert light energy into chemical energy, sustaining life on Earth. This complex process is divided into two main phases: the light-dependent reactions, which capture sunlight to produce energy-rich compounds, and the light-independent reactions, commonly referred to as the Calvin cycle. The Calvin cycle, named after the scientist Melvin Calvin who elucidated its pathway, operates in the stroma of chloroplasts and does not directly use light. Instead, it uses the products of the light-dependent reactions, ATP and NADPH, to fix atmospheric carbon dioxide (CO2) into organic molecules, ultimately synthesizing glucose for the organism's use.The Inputs and Outputs of the Calvin Cycle
The Calvin cycle is a biochemical pathway that uses carbon dioxide (CO2), nicotinamide adenine dinucleotide phosphate (NADPH), and adenosine triphosphate (ATP) as substrates to produce glucose. The general stoichiometric equation for the Calvin cycle is: 6 CO2 + 12 NADPH + 18 ATP + 12 H2O → C6H12O6 + 12 NADP+ + 18 ADP + 18 Pi + 6 H2O. This equation demonstrates the conversion of CO2 into glucose, with NADPH providing reducing power and ATP supplying the energy required for the synthesis. Water is both consumed and produced in the process, maintaining the balance of hydrogen in the cycle.The Sequential Phases of the Calvin Cycle
The Calvin cycle progresses through three distinct phases: carbon fixation, reduction, and regeneration of the ribulose bisphosphate (RuBP). In the carbon fixation phase, CO2 is attached to RuBP, a five-carbon sugar, facilitated by the enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO), resulting in an unstable six-carbon intermediate that immediately splits into two molecules of 3-phosphoglycerate (3-PGA). During the reduction phase, ATP and NADPH are used to convert 3-PGA into glyceraldehyde-3-phosphate (G3P), a three-carbon sugar. For every three turns of the cycle, five G3P molecules are used to regenerate RuBP, and one G3P molecule exits the cycle to contribute to the formation of glucose and other carbohydrates.Synthesis of Glucose and Regeneration of RuBP
The Calvin cycle not only regenerates its starting molecule, RuBP, but also produces glyceraldehyde-3-phosphate (G3P), which is a precursor for glucose and other carbohydrates. For the synthesis of one glucose molecule, two G3P molecules are required, which are obtained from six turns of the cycle. The remaining G3P molecules are recycled to regenerate RuBP, ensuring the continuity of the cycle. This regeneration phase is energy-intensive, requiring further ATP to phosphorylate the intermediates, thereby reforming RuBP to accept new CO2 molecules in subsequent cycles.Essential Insights into the Calvin Cycle
The Calvin cycle is an essential component of photosynthesis, enabling plants to synthesize glucose from carbon dioxide and water, independent of light. This cycle takes place in the chloroplast stroma and relies on the energy carriers ATP and NADPH, produced during the light-dependent reactions. The Calvin cycle is a cyclical series of reactions that includes carbon fixation, reduction, and regeneration phases, each playing a critical role in the continuous synthesis of carbohydrates. Understanding the Calvin cycle is fundamental to comprehending how plants convert inorganic carbon into organic compounds, fueling the biosphere and providing the basis for life on Earth.
Show More
Overview of Photosynthesis
Definition of Photosynthesis
Photosynthesis is the process by which plants, algae, and certain bacteria convert light energy into chemical energy
Light-Dependent Reactions
Definition of Light-Dependent Reactions
Light-dependent reactions are the first phase of photosynthesis, in which sunlight is captured to produce energy-rich compounds
Products of Light-Dependent Reactions
The products of light-dependent reactions, ATP and NADPH, are used in the Calvin cycle to fix carbon dioxide
Light-Independent Reactions (Calvin Cycle)
Definition of Calvin Cycle
The Calvin cycle is the second phase of photosynthesis, in which ATP and NADPH are used to fix carbon dioxide into organic molecules
Phases of the Calvin Cycle
The Calvin cycle progresses through three phases: carbon fixation, reduction, and regeneration of the starting molecule
Role of ATP and NADPH in the Calvin Cycle
ATP and NADPH provide the energy and reducing power, respectively, for the synthesis of glucose in the Calvin cycle
Stoichiometry of the Calvin Cycle
General Equation of the Calvin Cycle
The general stoichiometric equation for the Calvin cycle shows the conversion of carbon dioxide into glucose, with the use of ATP and NADPH
Role of Water in the Calvin Cycle
Water is both consumed and produced in the Calvin cycle, maintaining the balance of hydrogen in the process
Regeneration of RuBP
The regeneration of the starting molecule, RuBP, is a crucial step in the Calvin cycle, requiring ATP to continue the cycle
Importance of the Calvin Cycle
Role in Glucose Production
The Calvin cycle produces glyceraldehyde-3-phosphate (G3P), a precursor for glucose and other carbohydrates
Recycling of G3P
The remaining G3P molecules are recycled to regenerate RuBP, ensuring the continuity of the Calvin cycle
Energy Intensity of the Calvin Cycle
The regeneration phase of the Calvin cycle is energy-intensive, requiring additional ATP to reform RuBP and continue the cycle
Significance of the Calvin Cycle in the Biosphere
Location and Energy Source
The Calvin cycle takes place in the chloroplast stroma and relies on the energy carriers ATP and NADPH, produced during the light-dependent reactions
Continuous Synthesis of Carbohydrates
The cyclical nature of the Calvin cycle allows for the continuous synthesis of carbohydrates, providing the basis for life on Earth
The Calvin Cycle: A Key Process in Photosynthesis
Learn with Algor Education flashcards
Click on each Card to learn more about the topic
00
Photosynthesis critical role
Converts light energy to chemical energy, sustains life on Earth.
01
Photosynthesis two main phases
Light-dependent reactions produce energy-rich compounds; Calvin cycle fixes CO2 into glucose.
02
Light-independent reactions other name
Commonly known as the Calvin cycle.
