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B3.0 > Engineering Photosynthesis I: Bypassing Respiration > Flashcards

Engineering Photosynthesis I: Bypassing Respiration Flashcards

1
Q

Human pop growth

A
  • 2050: 9-10bn
  • average increase: c75mill/year; 1.1% (Germany)
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2
Q

Consumption trends

A
  • 2050: c3400kcal/person/day
  • ^c15kcal/person/year; 0.6%
  • 1/5th slice of bread
  • 78 million loaves / day
  • 2026: 15mill tonnes > wheat; 51,000km^2 (France)
  • 2,340,000m^2 cows
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3
Q

2050

A

We need to produce c70% more food

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4
Q

Crop yield improvements

A
  • have not kept pace w demand
  • 1.1% since 1960/year
  • 0.3% > land use/year
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5
Q

Land use

A
  • c15bn trees
  • c30% GHGs
  • CO2 release
  • < biodiversity; intensive megafarms = ecological deserts
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6
Q

Fun facts

A
  • there are 10 more humans by mass than all wild animals combined
  • 1/2 arable land on earth is farms
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7
Q

We need to radically intensify

A

Food production / land area

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8
Q

RUBISCO

A
  • generated life from carbon
  • Evolved: > CO2 (105,000ppm) , <O2 (10ppm)
  • CO2 10,000x> O2
  • 3.2Bya
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9
Q

Now

A
  • CO2: 400ppm
  • O2: 210,000ppm (500x>)
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10
Q

RUBSICO reactions

A
  • both CO2 and O2 in separate reactions
  • low CO2 specificity over O2
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11
Q

RuBP + CO2 ->

A

3-PGA + 3-PGA

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12
Q

RuBP + O2 ->

A

3-PGA + 2-PG

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13
Q

Photorespiration

A
  • RUBISCO is busy
  • inherent costs
  • more frequent due to higher O2
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14
Q

Photolysis

A
  • splits water into proton and oxygen using light
  • oxygen producer
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15
Q

Fixing CO2 is relatively cheap

A

3ATP + 2NADPH

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16
Q

O2 fixing recovery is complicated and expensive

A
  • 2-PG inhibits TPI, SBPase and PFK; need to get it out of the chloroplast and degrade it, quickly!
  • 30-80% CO2 released for refixation (remainder used as glycine, serine)
  • 50% released CO2 escapes back into atmosphere
  • c5-10% NH4+ -> NH3 @ cytosolic pH (>10% of root uptake; needs refixing)
  • NH3 escape = 5% N losses
17
Q

Environmental effects on photo respiration

A
  • more frequent @ higher temperatures
  • 30% CO2 fixation reduction
18
Q

RUBISCO Evolution

A
  • very old
  • constrained by multiple factors
  • 1aa substitution every 7.2My
19
Q

Alternative solutions?

A
  • CAM, C4
  • O2:CO2
20
Q

Photorespiratory bypasses

A

1) GOC
2) Maurino
3) Ort
4) Peterhansel

21
Q

Common bypass themed

A
  • cut 2-PG off from mitochondrial/peroxisome route
  • liberate CO2 in chloroplast
  • prevents C and N losses
22
Q

GOC bypass

A

1) 2-PG -PGP (-P)—> glycolate
2) glycolate -GO (O2->H2O2) -> oxalate
3) oxalate -OO (O2-> H2O2) -> 2CO2

23
Q

H2O2 -> O2

A

CAT

24
Q

GOC bypass output

A

For every RUBISCO oxygenation:
- 2CO2 released in chloroplast (no ammonium liberation)
- 6ATP, 4NADPH to refix CO2

25
Q

Is a bypass working?

A

Measure normal plant w bypass at low and normal levels of oxygen

26
Q

GOC bypass assessment

A
  • 19% increase in ambient O2 photosynthesis
  • same increase when O2 small
  • methodological error
27
Q

Maurino bypass

A
  1. 2-PG -PGP (-P) -> glycolate
  2. Glycolate -GO (O2->H2O2) -> glyoxylate
  3. Glyoxylate -MS-> malate
  4. Malate -ME (NADP-> NADPH) -> pyruvate + CO2
  5. Pyruvate -PD (NAD-> NADH; CoA-> acetyl-CoA)-> CO2
28
Q

Maurino bypass output

A

For every RUBISCO oxygenation:
1. 1NADH
2. 1NADPH
3. 2CO2
4. No ammonium liberation
5. 6ATP + 4NADPH to refix CO2

29
Q

Maurino bypass assessment

A

No significant increase at ambient CO2

30
Q

Ort bypass

A
  1. 2-PG -PGP (-P) -> glycolate
  2. Glycolate -GDH (NAD->NADH) -> glyoxylate
  3. Glyoxylate -MS-> malate
  4. Malate -ME (NADP-> NADPH) -> pyruvate + CO2
  5. Pyruvate -PD (NAD-> NADH; CoA-> acetyl-CoA)-> CO2
31
Q

Ort bypass output

A
  • 2NADH
  • 1NADPH
  • 2CO2
  • no ammonium liberated
  • 6ATP, 4NADPH to refix
32
Q

Ort bypass

A

C30% increase in both

33
Q

Peterhansel pathway

A
  1. 2x 2-PG -PGP (-P) -> glycolate
  2. Glycolate -GD (NAD-> NADH) -> glyoxylate
  3. 2x glyoxylate = tartronic semialdehyde
  4. tartronic semialdehyde -GK (ATP-> ADP) -> glycerate
  5. Glycerate -(ATP->ADP)-> 3-PGA -> CBC
34
Q

Peterhansel pathway output

A

For every 2x 2-PG:
1. 1x ATP consumed
2. 1x NADH generated
3. 1x CO2 released
4. No ammonium liberation
5. 3ATP, 2NADPH to refix CO2

35
Q

Peterhansel assessment

A
  • c50% ^
36
Q

Camelina sativa

A
  • peterhansel
  • not commercialised : GMO
37
Q

Living carbon

A
  • poplar
  • Ort
  • commercialised
  • smol >

B3.0 (23 decks)

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