7C-Carbon Reactions

Summary

This video explains the Calvin cycle, the second stage of photosynthesis, where carbon dioxide is converted into sugars using energy from light reactions. It highlights the process occurring in the chloroplast stroma, involving ribulose bisphosphate (RuBP) and the enzyme Rubisco. The cycle comprises three phases: carbon fixation, reduction, and regeneration of RuBP. During these phases, ATP and NADPH are utilized to transform carbon dioxide and RuBP into glyceraldehyde 3-phosphate (G3P), which can be used to synthesize sucrose or starch. The video concludes with questions to reinforce understanding of the cycle's efficiency.

Takeaways

• 🌱 The Calvin cycle, also known as the carbon reactions, is the second stage of photosynthesis that synthesizes sugars.
• 🔋 It utilizes ATP and NADPH produced during the light reactions of photosynthesis.
• 💧 The cycle occurs in the stroma of chloroplasts, which contains its own DNA and enzymes necessary for metabolic processes.
• 🌬️ Carbon dioxide is a crucial reactant that enters the cycle, where it is fixed to form carbohydrates.
• 🔄 The Calvin cycle consists of three main phases: carbon fixation, reduction, and regeneration of ribulose 1,5-bisphosphate (RuBP).
• 📏 In the carbon fixation phase, CO₂ reacts with RuBP, forming an unstable 6-carbon compound that splits into two molecules of 3-phosphoglycerate (3-PGA).
• ⚡ In the reduction phase, 3-PGA is phosphorylated by ATP and reduced by NADPH, producing glyceraldehyde 3-phosphate (G3P).
• 🍬 Out of six G3P molecules produced, one exits the cycle to contribute to the synthesis of sucrose or starch.
• 🔄 The remaining five G3P molecules are used to regenerate three RuBP molecules, allowing the cycle to continue.
• 🔄 To produce one sucrose molecule, the cycle must turn six times, using 18 ATP and 12 NADPH in the process.

Q & A

What is the Calvin cycle also known as?

The Calvin cycle is also known as the carbon reactions or the Calvin-Benson cycle.

Where do the carbon reactions take place within the chloroplast?

The carbon reactions take place in the stroma, which is the fluid that fills the chloroplast.

What are the primary inputs required for the Calvin cycle?

The primary inputs required for the Calvin cycle are carbon dioxide (CO2), ATP, and NADPH, which are produced during the light reactions.

What is ribulose-1,5-bisphosphate (RuBP) and its role in the Calvin cycle?

Ribulose-1,5-bisphosphate (RuBP) is a 5-carbon compound that reacts with carbon dioxide during the carbon fixation phase of the Calvin cycle.

What enzyme catalyzes the reaction between CO2 and RuBP?

The enzyme that catalyzes the reaction between CO2 and RuBP is called ribulose bisphosphate carboxylase/oxygenase, commonly referred to as Rubisco.

What are the three phases of the Calvin cycle?

The three phases of the Calvin cycle are carbon fixation, reduction, and regeneration of RuBP.

What happens during the reduction phase of the Calvin cycle?

During the reduction phase, the six molecules of 3-phosphoglycerate (3-PGA) are phosphorylated by ATP and reduced by NADPH to produce glyceraldehyde-3-phosphate (G3P).

How many G3P molecules are produced in the cycle and how are they utilized?

Out of six G3P molecules produced, one exits the cycle to be synthesized into sugars like sucrose or starch, while the remaining five are used to regenerate RuBP.

What is the significance of regenerating RuBP?

Regenerating RuBP is essential because it allows the cycle to continue by preparing for the next round of carbon fixation.

How many turns of the Calvin cycle are needed to produce one molecule of sucrose?

To produce one molecule of sucrose, two turns of the Calvin cycle are needed.

In producing one sucrose molecule, how many ATP and NADPH molecules are used?

In producing one sucrose molecule, a total of 18 ATP and 12 NADPH molecules are used.