Photorespiration

TL;DR

Rubisco, a central enzyme in the Calvin cycle, can sometimes fix oxygen instead of carbon dioxide, leading to a less efficient process called photo-respiration.

Transcript

• [Voiceover] We have other videos that go into some depth on the Calvin cycle, and we'll refer to that in this video as the normal Calvin cycle, and the focus of this video is really a quirk that diverts us from the normal Calvin cycle, and it's a quirk due to this enzyme right here whose shorthand name is rubisco. So to get an appreciation for th... Read More

Key Insights

• 💆 Rubisco is a crucial enzyme in the Calvin cycle and accounts for approximately 20% of the protein mass in plant leaves.
• 🥺 Photo-respiration occurs when Rubisco fixes oxygen instead of carbon dioxide, leading to the production of a two-carbon molecule called phosphoglycolate.
• 😚 The process of salvaging the carbons lost in photo-respiration involves multiple steps and can be energetically costly for plants.

Questions & Answers

Q: How does Rubisco function in the Calvin cycle?

Rubisco acts as a carboxylase, fixing carbon dioxide and incorporating it into organic molecules during the Calvin cycle.

Q: What is the quirk of Rubisco in relation to photo-respiration?

The quirk is that Rubisco can sometimes fix oxygen instead of carbon dioxide, leading to the production of phosphate and the disruption of the Calvin cycle.

Q: Why does photo-respiration occur more frequently in hot conditions?

Under hot conditions, Rubisco has a higher affinity for oxygen and a lower affinity for carbon dioxide. Additionally, plant stomata close to conserve water, leading to an increased ratio of oxygen to carbon dioxide.

Q: Is photo-respiration detrimental to plants?

Photo-respiration is generally considered an inefficiency in the photosynthetic process and can be detrimental to plants. Some believe it may have been a side effect from ancient evolution when there was less oxygen in the atmosphere.

Summary & Key Takeaways

• The Calvin cycle is a process where carbon dioxide is fixed by the enzyme Rubisco to create organic molecules, ultimately leading to glucose production.

• Rubisco can sometimes fix oxygen instead of carbon dioxide, leading to a diversion in the process known as photo-respiration.

• Photo-respiration occurs more frequently in hot conditions when Rubisco has increased affinity for oxygen and the ratio of oxygen to carbon dioxide is higher.