Rubisco in C3, C4, and CAM photosynthesis Flashcards
(42 cards)
What is rubisco?
pivotal enzyme involved in initial carbon fixation during the light-independent stage of photosynthesis
What is a CAM plant?
plants that minimise photorespiration by separating initial carbon fixation and the remainder of the Calvin cycle over time
What is a C4 plant?
plants that minimise photorespiration by separating initial carbon fixation and the remainder of the Calvin cycle over space
What is a C3 plant?
plants with no evolved adaptation to minimise photorespiration
What is the light dependent stage of photosynthesis?
the first stage of photosynthesis, where light energy splits water molecules into oxygen and hydrogen inside the thylakoid membranes. Also known as the light-dependent reactions
What is the light independent stage of photosynthesis?
the second stage of photosynthesis where carbon dioxide is used to form glucose in the stroma of a chloroplast. Also known as the Calvin cycle, the dark stage, or the light-independent reactions
Why do plants cycle between carbon molecules?
Plants cannot convert CO2 directly into glucose as it would waste too much energy
What is the function of rubisco?
Controls the first reaction in the light-independent stage of photosynthesis
2. Reduction – NADPH donates electrons to (aka ‘reduces’) an intermediate three-carbon molecule in the cycle to produce G3P
What are the steps of Rubisco in the Calvin cycle?
- Carbon fixation
- Reduction
- Regeneration
What are the occurs in step 1 of Rubisco in the Calvin cycle?
- Carbon fixation – which refers to the conversion of CO2 and RuBP into 3-PGA. Here, we say that the carbon from the inorganic CO2 is ‘fixed’ into an organic compound. Rubisco is responsible for taking carbon from an inorganic, gaseous form (CO2) and incorporating it into an organic compound (3-PGA)
What are the occurs in step 2 of Rubisco in the Calvin cycle?
- Reduction – NADPH donates electrons to (aka ‘reduces’) an intermediate three-carbon molecule in the cycle to produce G3P
What are the occurs in step 3 of Rubisco in the Calvin cycle?
- Regeneration – the RuBP molecules needed to start the cycle again are reproduced.
What is carbon fixation?
the process in living organisms where inorganic carbon, typically within carbon dioxide, is converted into organic compounds such as glucose. Carbon fixation is a central part of the light-independent stage of photosynthesis
What is photorespiration?
a wasteful process in plants initiated by Rubisco that limits photosynthesis
Why is photorespiration so harmful to plants?
By binding O2 and undertaking photorespiration, photosynthesis is disrupted as CO2 loses an opportunity to bind with Rubisco. Less photosynthesis means less glucose is produced, which, combined with wasted energy used in the photorespiration pathway, negatively impacts a plant’s ability to grow, survive, and reproduce.
What is the flaw of rubisco?
Sometimes, rather than using CO2 as a substrate, it uses O2 instead. When Rubisco binds to O2 instead, a different reaction called photorespiration occurs.
What are the key factors that influence what rubisco binds to?
Temperature and substrate concentration
How does temperature influence what rubisco binds to?
at regular or low temperatures, Rubisco’s affinity for CO2 is far greater than that for O2. At higher temperatures, the affinity for O2 is higher, leading to Rubisco binding oxygen more often
What is affinity?
the tendency of a molecule/atom to bind or react with another molecule/atom
How does substrate concentration influence what rubisco binds to?
The more substrate is present, the greater chance it can bind to an enzyme and undergo a reaction. Because of this, plants ‘want’ to expose Rubisco to a high CO2 concentration and a low O2 concentration (so as to maximise photosynthesis). To facilitate this, the stomata of the plant leaves open to allow CO2 to enter the plant, while O2 and water vapour simultaneously diffuse out of the plant. However, when a plant needs to conserve water it will close its stomata, causing the O2 produced during the light-dependent stage of photosynthesis to build up inside its cells. A greater concentration of oxygen in the cells leads to increased photorespiration.
Why does photorespiration increase in hot and dry conditions?
Rubisco’s affinity changes as temperature increases more O2 is bound rather than CO2
increased water loss, stomata close, O2 from the light-dependent reactions trapped in the leaf O2 concentration increases around rubisco
Where does the Calvin cycle occur in C3 photosynthesis?
Mesophyll cell
Where does the Calvin cycle occur in C4 photosynthesis?
initial carbon fixation occurs in a mesophyll cell, however, the remaining Calvin cycle occurs in bundle-sheath cells
What are the steps of the light independent reactions in C4 plants?
- Atmospheric CO2 enters mesophyll cells
- Oxaloacetate is converted to malate
- Malate breaks down and releases CO2
- Pyruvate formed
- PEP contributes to fixation of CO2 and production of oxaloacetate
