Question

\(\mathrm{CO}_{2}\) combines with RuBP in the presence of enzyme RuBisCO to form \(3-P G A\). This process of Calvin cycle is included under (a) carboxylation (b) oxygenation (c) reduction (d) regeneration.

Short answer

The process of Calvin cycle described is included under (a) carboxylation.

Step-by-step solution

Identify the Process

Analyze the given information to understand what biological process is being described. Here, the combination of \(\mathrm{CO}_{2}\) with RuBP in the presence of the enzyme RuBisCO is a primary reaction in the Calvin cycle.

Understand Terminology

Differentiate between the terms. Carboxylation involves the addition of \(\mathrm{CO}_{2}\) to a compound. Oxygenation involves the addition of oxygen to a compound. Reduction refers to the gain of electrons and the reduction in oxidation state. Regeneration pertains to the restoration of RuBP for the cycle to continue.

Determine the Correct Option

The initial step where \(\mathrm{CO}_{2}\) is fixed onto RuBP to form 3-PGA is an example of carboxylation, since it involves the addition of carbon dioxide to RuBP.

Key concepts

Carboxylation

Carboxylation is a crucial initial step in the Calvin cycle, which is part of the photosynthesis process. In this phase, carbon dioxide ((CO_{2})) from the atmosphere is attached to a five-carbon sugar molecule called ribulose bisphosphate (RuBP). This reaction is catalyzed by an enzyme known as RuBisCO. By incorporating (CO_{2}) into an organic molecule, carboxylation sets the stage for the subsequent steps of the Calvin cycle, leading to the production of glucose and other carbohydrates that plants use for energy. It's important to note that carboxylation is an energy-consuming process, relying on ATP and NADPH produced during the light-dependent reactions of photosynthesis.

The significance of carboxylation cannot be overstated as it essentially initiates the conversion of inorganic carbon into organic forms, which is fundamental for life on Earth. This process sustains the global carbon cycle and contributes to the maintenance of atmospheric carbon dioxide levels.

RuBisCO enzyme

The RuBisCO enzyme, short for ribulose-1,5-bisphosphate carboxylase/oxygenase, is considered to be one of the most important enzymes on the planet due to its role in the Calvin cycle of photosynthesis. It's responsible for catalyzing the first major step of carbon fixation, which is carboxylation. RuBisCO has this dual name because it can also catalyze the oxygenation of RuBP, depending on the concentration of (CO_{2}) and oxygen in the surrounding environment.

Despite its pivotal role, RuBisCO is not a particularly efficient enzyme, as it can also react with oxygen, leading to a wasteful process called photorespiration. This side reaction can significantly affect the overall efficiency of photosynthesis, mainly in conditions where (CO_{2}) levels are low and oxygen levels are high. Researchers are looking for ways to improve the function of RuBisCO through genetic engineering, with the goal of increasing crop yields and improving food security.

Photosynthesis processes

Photosynthesis is a complex, multi-step process that plants, algae, and certain bacteria use to convert light energy into chemical energy. This process can be divided into two main stages: the light-dependent reactions and the Calvin cycle, which is also known as the light-independent reactions or the dark phase. In the light-dependent reactions, light energy is harnessed to produce ATP and NADPH. These energy carriers are then used in the Calvin cycle, where (CO_{2}) fixation takes place.

The Calvin cycle has several key steps: carboxylation, reduction, regeneration of RuBP, and the formation of glucose and other sugars. While carboxylation is the first step, it's followed by the reduction of 3-phosphoglyceric acid (3-PGA) to glyceraldehyde-3-phosphate (G3P), using ATP and NADPH. Some G3P molecules exit the cycle to form glucose, while the majority are used to regenerate RuBP, enabling the cycle to continue. Understanding the intricate details of these photosynthesis processes is essential for grasping how plants produce the biomass that supports most life on Earth.

3-phosphoglyceric acid (3-PGA)

3-phosphoglyceric acid (3-PGA) is a three-carbon molecule that is the first stable product of carboxylation during the Calvin cycle. When (CO_{2}) is fixed to RuBP by the action of RuBisCO, the resulting six-carbon intermediate immediately breaks down into two molecules of 3-PGA. This compound is pivotal as it is subsequently reduced and transformed through a series of reactions within the Calvin cycle.

The transformation of 3-PGA involves the use of ATP and NADPH from the light-dependent reactions to ultimately form glyceraldehyde-3-phosphate (G3P). G3P is a precursor for the synthesis of glucose and other carbohydrates, which are vital for plant growth and development. The efficient conversion of 3-PGA to these energy-rich compounds reflects the fundamental importance of the Calvin cycle in biosynthesis and the global carbon cycle.