lec 14 slide 14

what is it called when the process requires CO2, but what if there is no CO2 around

photorespiration

what does Rubisco stand for

Ribulose 1,5-biphosphate carboxylase/oxygenase

what are the two activities of rubisco

• carboxylase activity (adds CO2)

• Oxygenase activity (adds O2)

what happens during Rubisco’s carboxylase activity

CO2 is added to ribulose 1,5-biphosphate producing 2 molecules of 3-phosphoglycerate (3-PGA)

when does photorespiration occur

when CO2 is low and O2 is high

What happens during Rubisco’s oxygenase activity

O2 is added to ribulose 1,5-biphosphate producing

1 molecule of 3-phosphoglycerate (3-PGA)

1 molecule of phosphoglycolate

oxygen will be used to oxygenate ribulose 1.5-biphosphate producing what

water

O2 is added to ribulose 1,5-biphosphate producing

1 molecule of 3-phosphoglycerate (3-PGA)

1 molecule of phosphoglycolate

this is catalyzed by rubisco via its oxygenase activity

Rubisco can do either reaction

using its CARBOYLASE activity, it can be part of the CALVIN CYCLE ‘

using its OXYGENASE activity, it can be part of PHOTORESPIRATION

problem with producing less 3-PGA) 3-phosphoglycerate

produces less sugar production which is needed for calvin cycle to make glyceraldehyde 3 phosphate

what is the probglem with producing phosphoglycolate

it not only inhibits photosynthesis BUT also needs to be recycled to ribulose 1,5-biphosphate

problem with recycling phosphoglycolate back to ribulose 1,5-biphosphate

the cell has to use energy and reducing power to give off/releases CO2 and ammonia

why is photorespiration bad for plants

its using energy to give off carbon when the goal is the fix carbon

what does phosphoglycolate do in the cell

inhibits photosyntthesis and must be recycled back to RuBP using energy

what is lost during the recycling of phosphoglycolate

CO2, Ammonia, and energy and reducing power

how often does Rubisco perform carboxylation

75% carboxylation

how often does rubisco perform oxygenation

25$ oxygenation

there is more than ____ more oxygen than CO2 in our current atmosphere

500 times

What reaction does rubisco favor

carboxylation

why wasnt rubsicos oxygenase activity selected against early in the process of the evolution of carbon fixation

the system evolved under low oxygen levels so the oxygenase activity wasnt a problem like it is today

why does rubisco still favor carboxylation despite high O2 levels

it has a higher affinity for CO2 than O2

what plants have evolved in way to deal with low oxygen levels by using differen cell types.

C4 plants

what is the main goal of Calvin cycle

to fix carbon into sugars

how do C4 plants protect Rubisco from oxygen

CO2 is first fixed in air-exposed cells

then transported to rubsico-containg cells

keeps high CO2/low O2 environment