Question

Опишите механизм цикла Кальвина

Answer 1

Две молекулы глицеральдегид-3-фосфата используются для синтеза глюкозы. Цикл состоит из трёх стадий: на первой под действием фермента рибулозобисфосфат-карбоксилаза/оксигеназа происходит присоединение CO2 к рибулозо-1,5-дифосфату и расщепление полученной гексозы на две молекулы 3-фосфоглицериновой кислоты (3-ФГК).

Answer 2

The Calvin Cycle Mechanism

The Calvin Cycle, also known as the Calvin-Benson cycle or the C3 cycle, is a series of biochemical reactions that take place in the stroma of chloroplasts during photosynthesis. It is named after Melvin Calvin, who won the Nobel Prize in Chemistry in 1961 for his research on the cycle.

The Calvin Cycle is responsible for converting carbon dioxide (CO2) into glucose, which is a form of stored energy. It is an essential part of the process by which plants and some bacteria produce organic compounds, including sugars, from carbon dioxide and water.

The Calvin Cycle can be divided into three main stages: carbon fixation, reduction, and regeneration.

Carbon Fixation

In the first stage of the Calvin Cycle, carbon dioxide from the atmosphere is captured and converted into an organic molecule. This process is called carbon fixation. The enzyme responsible for this step is called RuBisCO (Ribulose-1,5-bisphosphate carboxylase/oxygenase). RuBisCO catalyzes the reaction between carbon dioxide and a five-carbon sugar called ribulose-1,5-bisphosphate (RuBP), resulting in the formation of two molecules of a three-carbon compound called 3-phosphoglycerate (3-PGA).

Reduction

In the second stage of the Calvin Cycle, the energy stored in ATP (adenosine triphosphate) and NADPH (nicotinamide adenine dinucleotide phosphate) is used to convert the 3-phosphoglycerate molecules into a three-carbon sugar called glyceraldehyde-3-phosphate (G3P). This step requires the input of energy and reducing power. Some of the G3P molecules are used to produce glucose, while others are used to regenerate the starting molecule, RuBP.

Regeneration

In the third stage of the Calvin Cycle, the remaining G3P molecules are used to regenerate RuBP. This step involves a series of reactions that rearrange the carbon atoms in the G3P molecules to form RuBP. The regeneration of RuBP allows the cycle to continue, ensuring a constant supply of RuBP for carbon fixation.

Summary

To summarize, the Calvin Cycle is a series of biochemical reactions that occur in the chloroplasts of plants and some bacteria. It converts carbon dioxide into glucose, which is a form of stored energy. The cycle consists of three stages: carbon fixation, reduction, and regeneration. Carbon dioxide is captured and converted into organic molecules in the carbon fixation stage. In the reduction stage, ATP and NADPH are used to convert the organic molecules into a three-carbon sugar. Finally, in the regeneration stage, the remaining three-carbon sugars are used to regenerate the starting molecule, ensuring a continuous supply of carbon dioxide fixation.

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