Adaptations to low CO2 Flashcards
What did rubisco start as?
Did not start as a carbon fixing enzyme. It was originally involved with nucleotide metabolism.
It evolved in an O2 free atmosphere.
What does rubisco fix aswel as CO2?
Fixes O2 and CO2.
This means oxygenation competes with carboxylation (reducing efficiency) and oxygenation produces a toxic product: 2-PGA.
How are the negatives of oxygenation by rubisco solved?
Photorespiration uses the toxic products 2-PGA (however, requires ATP and releases CO2)
Carbon concentrating mechanisms (CCMs) concentrate CO2 and rubiscos active site to minimise oxygenation.
What is the carbon concentrating mechanism?
Low concentration CO2 is pumped against concentration gradient. (Requires ATP).
When was RCO2 low?
During the carboniferous period, coal beds were being laid.
What is RCO2?
CO2 relative to today.
1 = today
20 = 20 times higher than today
What happens to the relative solubility and relative specificity of rubisco in different temperatures?
As temperature increases:
- Relative solubility decreases
- Relative specificity decreases (rubisco is less able to grab correct molecules)
What happens to rubisco in water?
Local CO2 depletion: CO2 diffusion is 100 times slower in water than air.
What is the main source of CO2 in the ocean for rubisco?
From bicarbonate, chemical equilibrium is low.
Carbon concentration is sensitive to pH
What are 2 examples of CCMs for C3 photosynthesis?
Cyanobacteria:
- CCMs in all cyanobacteria. Two lineages (alpha and beta)
- CO2 + H2o -> H + HCO3
- Catalysed by carbonic anhydrase.
- Leaked CO2 is recycled
Eukaryotic algae:
- Most have a CCM. Exceptions live in well aerated water, because theres lots of mixing of gas, lots of CO2
What are the differences between C4 and CAM photosynthesis?
C4:
- C fixation in mesophyll cells
- CO2 release in bundle sheath
CAM:
- C fixation at night (stomata open)
- CO2 released in the day (stomata closed)
What drove the evolution of CCMs?
Cenozoic global change, major intervals of low CO2, high O2, glaciation and dry climates.
How many times has C4 photosynthesis evolved?
More than 70 times.
What is different about C4 photosynthesis plants?
They favour carboxylation over oxygenation, minimises photorespiration.
Saturates rubisco with CO2
However, needs high temps and has an energy cost.
When has C4 photosynthesis evolved from?
Oligocene period.
In low CO2, dry conditions.
Cold meant water was locked up in ice sheets and atmosphere could not hold much water.
