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Rubisco: How the enzyme responsible for life makes mistakes

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Rubisco plays an important role in one of the most important processes of life: photosynthesis, which occurs only in the chloroplasts of plant cells. Photosynthesis is divided into two different reactions: light-dependent and light-independent.

Chloroplast of a cell
Inside the chloroplast of a cell

Light-independent reactions have a process called the Calvin Cycle, which is where Rubisco does its work. The goal of the Calvin Cycle is to take the products from light-dependent reactions–NADPH and ATP–and CO2 from the air to produce G3P, which becomes sugar at the end of

The substrate needs to be able to fit in the enzyme's shape
How enzymes and substrates fit

photosynthesis. Rubisco is an enzyme, meaning that it catalyzes reactions so the reaction occurs faster. Every enzyme has a specific shape, so the substrate, which is what the enzyme reacts with, can fit in the shape.

Rubisco attaches CO2 to RuBP at the end of the Calvin Cycle, G3P can be produced
Use of Rubisco in the Calvin Cycle

In the first step of the Calvin Cycle, Rubisco takes CO2, the substrate, and attaches it to RuBP, a 5-carbon sugar. However, the issue is that O2 is only slightly smaller than CO2, which causes Rubisco to mistakenly take oxygen instead of carbon dioxide. To fix this mistake, the plant’s energy is wasted. Despite Rubisco’s important role, it often fails to do it accurately and has an error rate of over 20% and higher in less desirable environments, like in high temperatures. 

Due to Rubisco’s inefficiency, scientists like those at RIPE (Realizing Increased Photosynthetic Efficiency) are working to genetically modify Rubisco to yield better results. If Rubisco’s accuracy can be increased, plants would be able to use the otherwise wasted energy that comes from fixing Rubisco’s errors to produce more crops, which would improve the efficiency of food production to help mitigate world hunger.

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