LECTURE 10 - Photosynthesis

Question 1

photosynthesis

Answer 1

6 CO2(g) + 6 H2O(l) –> C6H12O6(aq) + 6 O2(g)

Question 2

rubisco

Answer 2

also known as RuBisCO (Ribulose bisphosphate carboxylase/oxygenase)
occurs in the chloroplast stroma (LI stage in stroma remember)

Question 3

LI stage

Answer 3

carboxylation :
CO2 + H20 –rubisco –> 3-phosphoglycerate (3-PGA)

reduction:
3-PGA –> G3P (glyceraldehyde-3-phosphate)
reducing agents aka oxidation reactions for this reduction:
ATP –> ADP + Pi
NADPH –> NADP+

G3P –> TP (triose phosphate) –> sucrose/starch etc

regeneration:
G3P –> RuBP (ribulose-1,5-bisphosphate)
ATP –> ADP + Pi

Question 4

photorespiration

Answer 4

uses O2 instead of CO2
produces 3-PGA and also 2-phosphoglycolate
2-phosphoglycolate has to be detoxified and uses the chloroplast, peroxisome and mitochrondrion, as well as ATP and releases CO2 instead, very wasteful and counterproductive

Question 5

C4 photosynthesis

Answer 5

in C3, carbon dioxide is fixed directly into (3-PGA).
in C4, carbon dioxide combines with phosphoenolpyruvate (PEP) using PEP carboxylase (PEPC) = C4 acids
The C4 acids produced by PEP carboxylase in the mesophyll cells are then transported to bundle sheath cells, where they release CO2.
–> creates a high concentration of CO2 in close proximity to Rubisco
–> lower chance of photorespiration

Question 6

Crassulacean acid metabolism (CAM) photosynthesis

Answer 6

Solves photorespiration and saves water (relative to C3 or C4)
–> opens stomata at night only for CO2
–> same inital step in C4