Regulation C4 and CAM

Question 1

What does calvin cycle activity depend on

Answer 1

Environmental conditions e.g. pH, Mg2+, NADPH

Question 2

What is the optimum pH for the light reaction

Answer 2

pH8

Question 3

How does Rubisco activate>

Answer 3

Uses hydrolysis of ATP to open active site loop (activase_

Question 4

Example of Rubisco inhibitor

Answer 4

CA1P - some plants make this compound - degraded by CA1P phosphatase and removed from Rubisco by activase

Question 5

Thioredoxin

Answer 5

12kDa protein containing key cysteines with redox active S-S. Reduced form activates many enzymes

Question 6

How do you get reduced form of thioredoxin

Answer 6

Coupled to ferredoxin activity via ferredoxin-thioredoxin reductase (4Fe-4S cluster)

Question 7

How are enzymes inactivated

Answer 7

CP12 small intrinsically disordered protein with conserved cysteine residues

Question 8

How does regulatory inhibition occur

Answer 8

Disulphide bond formation

Question 9

Oxidised form of CP12

Answer 9

Binds GAPDH and PRK (found on either side of rubisco) - forms inactive complex

Question 10

What is the CO2 compensation point

Answer 10

[CO2] needed for net photosynthesis

Question 11

How do plants withstand water-stress

Answer 11

Suppress photorespiration by C4

Question 12

How are high rates of wasteful photorespiration reduced

Answer 12

Concentrate CO2 close to the site of calvin cycle enzymes

Question 13

What do C4 compounds enable CO2 to do

Answer 13

Spatially transfer CO2 from mesophyll cells to bundle-sheath cells (costs energy +12ATP)

Question 14

How much does it cost to move 1 CO2

Answer 14

2 ATP

Question 15

How are C4 plants highly productive

Answer 15

Adapt to high temp and low CO2,more resistant to water stress, more productive

Question 16

CAM

Answer 16

Crassulacean acid metabolism - mostly desert xerophytes (tend to be slow growing and resistant to water stress)

Question 17

How do CAM (C4) plants work

Answer 17

Stomata close in day to prevent water loss and stop CO2 absorption. At night CO2 in and fixed into malate by C4 stored in vacuoles for use in the day

Question 18

Avoiding photorespiration

Answer 18

C4 & CAM, concentrate CO2 around rubisco, increase Co2:O2 ratio, decrease oxygenation, costs extra ATP

Question 19

What is role of C4 and CAM

Answer 19

Biochemical pumps to concentrate CO2 in cells and to reduce photorespiration

Question 20

CCM

Answer 20

Carbon concentrating mechanisms in cyanobacteria

Question 21

What is rubisco regulated by

Answer 21

Mg2+ and pH

Question 22

Carboxysome

Answer 22

Class of bacterial microcompartments - contains rubisco and carbonic anhydrase inside - CO2 rich - not in chloroplasts