Grand Challenges: Photosynthesis

Question 1

Light dependent reactions

Answer 1

Light energy absorbed - change into chemical energy in form of ATP
Inside chloroplast thylakoid membrames embedded in stroma
Stroma contains enzymes for CB cycle
Takes ATP and NADPH to fix CO2 into sugar

Question 2

PSII

Answer 2

Absorb light energy by light harvesting complexes
Chl molecules absorb energy and funnel energy into reaction centre
Energy used to take e- out of water to release O2
e- passed down e- transport chain

Question 3

e- transport chain

Answer 3

Energy shifted to carrier molecule (pheophytin)
e- passed through series of proteins to membranes
Some energy lost through transfering protons across membrane
Use this proton flow to generate ATP
e- passed to PSI - e- gets more light energy from chlorophyll
Series of reactions to produce NADPH

Question 4

Light independent reactions

Answer 4

Plant uses ATP and NADPH to fix CO2 via CB cycle to make sugar

Question 5

Excessive light

Answer 5

Photons can generate ROS
Destroys protein structures and photosynthetic machinery
Photoinhibition - photosynth stops; excess energy diverted and dissipated

Question 6

Rubisco

Answer 6

Abundant enzyme
Fix CO2 and move carbon into sugars
High CO2 = photosynth
Low CO2 = photoresp - minimise this

Question 7

Photorespiration

Answer 7

Rubisco has high affinity for oxygen
Photoresp is inefficient and causes loss of carbon fixation
Decrease this to increase yields
Want less 3 phosphoglycerate and more 2 phosphoglycolate

Question 8

Improve Rubisco

Answer 8

Different versions between species

Low specificity: takes in anything but doesn’t distinguish between CO2 and O2; high rate of reaction
High specificity: distinguishes CO2 and O2; lower rate of reaction

Climate change so may be better to have low specificity one

Question 9

Decrease photoresp

Answer 9

Increase CO2 conc around rubisco - engineer crops
Local changes around pyrenoids and carboxysomes to fix CO2 into bicarbonate
Localised structure created to focus rubisco and CO2
Put carboxysome or pyrenoid into crop to make more efficient photosynth

Question 10

Change plant anatomy and biochem

Answer 10

Diff mechanism to fic CO2
Fix CO2 into oxaloacetate - 4C molecule
Move metabolite into neighbouring cell (bundle sheath)
Pump malate molecule
Release CO2 just in bundle sheath
Higher conc of CO2 for rubsico

Question 11

C4 photosynthesis

Answer 11

Convergent evolution
Engineer into diff cell types - express genes at right time and right place
Metabolic engineering: recycle glycolate into CB cycle so plant can use sugar to increase yield
Replenish ribulose 1, 5 biphospate quicker
Increase rate of cycle and C fixation by overexpressing enzymes