Carbon Fixation

Question 1

how are 3C intermediates made?

Answer 1

• degradation of larger molecules

- carbon fixation in plants

Question 2

carbon fixation cycle

Answer 2

calvin cycle

Question 3

key intermediate

Answer 3

ribulose 1,5 - bisphosphate (RuBP) constantly regenerate

Question 4

net result

Answer 4

CO2 reduction with NADPH

Question 5

3 stages of Calvin cycle

Answer 5

• CO2 fixation
• reduction
• RuBP regeneration

Question 6

main enzyme

Answer 6

Mg dependent rubisco w/ dual activity: carboxylation and oxygenation (competing processes)
- 8 small and 8 large subunits

Question 7

Step 1: Fixation

Answer 7

RuBP and CO2 –> 2 3-phosphoglycerate

Question 8

Step 2: reduction

Answer 8

3-phosphoglycerate reduced to glyceraldehyde 3-phosphate using NADPH and ATP

Question 9

Step 3: RuBP regeneration

Answer 9

important

Question 10

Rubisco oxygenase reaction

Answer 10

photorespiration

- rubisco reacts with O2 instead of CO2 making 3-phosphoglycerate and phosphoglycolate (catalytic imperfection)

Question 11

C2 pathway (glycolate pathway)

Answer 11

• ATP consuming
• C2 fragment recovery from photorespiration
• 2 phosphoglycolates converted to Ser + CO2

Question 12

C3 Photosynthesis disadvantages

Answer 12

• water loss

- photorespiration

Question 13

CAM Plants

Answer 13

captures CO2 at night and fixed to oxaloacetate via PEPCK; oxaloacetate is reduced to malate which releases CO2 in the daytime to resume with CO2 fixation in the day

Question 14

C4 Plants

Answer 14

bypass C3 step by fixing CO2 into a C4 compound which is delivered to bundle sheath cells in form of malate

Question 15

CAM C4 advantages

Answer 15

Water conservation

Reduced photorespiration

Question 16

C3 vs C4

Answer 16

C4 grow better in hot climates

C3 have advantage in cooler climate due to lower energy use