Types of Carbon Concentrating Mechanism CCM Overview Undergraduate
Types of Carbon Concentrating Mechanism (CCM) - Overview Undergraduate level notes
Biochemical Mechanisms in Plants �Variations on C 3 photosynthesis in which the drawing down of CO 2 is not directly performed by Ru. Bis. CO �Carbon is initially “fixed” as a C 4 acid by phosphoenolpyruvate carboxylase (PEPC), which is delivered to Ru. Bis. CO and converted back to CO 2, before being fixed as C 3 compounds via the CBB cycle. �Two main variants: C 4 and CAM (some variants are also found in aquatic plants).
C 4 and CAM - overview �C 4 photosynthesis is a spatial separation of the drawing down of CO 2 and its actual fixation by Ru. Bis. CO. �This spatial separation is facilitated by Kranz anatomy. �CAM is a temporal separation of the two processes, facilitated in higher plants by a specific, phased pattern of stomatal opening and closing.
Biophysical Mechanisms �Variants in algae (eukaryotic) and in cyanobacteria (prokaryotic). �Less well characterised than biochemical CCMs in higher plants. �In algae, the main CCM component is the pyrenoid and in cyanobacteria, it is the carboxysome.
The Pyrenoid and Carboxysome �Pyrenoid in algae is where most of the Ru. Bis. CO in the chloroplast is found, but is not membrane-bound. �Pyrenoid is part of a CCM comprising a series of bicarbonate (HCO 3 -) pumps and carbonic anhydrases (to interconvert HCO 3 - and CO 2). �Carboxysome is a more clearly defined microcompartment of cyanobacterial cells and has a protein shell; bicarbonate ions are also delivered by active transport.
Summary �Biochemical vs biophysical mechanisms �Biochemical: C 4 and CAM (higher plants and some algae); Biophysical: pyrenoid (algae) and carboxysome (cyanobacteria). �Biochemical CCMs separate CO 2 drawdown and fixation; biophysical CCMs actively concentrate CO 2 around Ru. Bis. CO by transporting HCO 3 -.
- Slides: 6