Lecture 7 Flashcards
How does CO2 enter land plants?
Enter leaves and photosynthetic cells via stomata (gas exchange)
How does CO2 enter algae or cyanobacteria?
Dissolved in water
In which type of plant is the stomata lost?
Liverworts
When did the stomata appear to have evolved?
Prior to bryophytes
What do the light reactions provide for the Calvin cycle?
3 ATP from cyclic photophosphorylation
6 ATP from non cyclic photophosphorylation
6 NADPH from Noncyclic electron flow
What is the first stage of the Calvin cycle and explain what happens.
Fixation
RuBP relocates H atom (tautomerization)
Carboxylation OF RuBP
Rubisco catalyzes the reaction and RuBP carboxylase/oxygenase
The 6-carbon intermediate is unstable and rapidly hydrolyzed into 2 molecules of 3-phosphoglycerate (PGA)
What is the second stage of the Calvin cycle and explain what happens.
Reduction
PGA is phosphorylated (6 molecules would require 6ATP)
It makes 1, 3-biphosphoglycerate which is reduced using NADPH’s H
1 phosphate is removed
6 molecules of PGAL are produced
Why is the Calvin cycle also called C3 photosynthesis?
The first stable intermediate is a 3-carbon compound
How many CO2 per turns of the Calvin cycle are fixed?
1
What happens every three turns of the Calvin cycle?
1 of 6 molecules of PGAL leaves for making sugars and starches
How many PGALs are required to make 3 RuBP
5
What is stage three of the Calvin cycle?
Regeneration of acceptors using 3 ATP
What is Rubisco and what does it do?
Ribulose-1,5 bisphosphate carboxylase/oxgenase
Forms a bridge between life and the lifeless
Attaches CO2 toRuBP making 6-carbon intermediate
Which hydrolyses into 2 3-carbon phosphoglycerate
Why do we say that Rubisco is inefficient?
A typical enzyme fixes 1000 molecules per second while it fixes 3CO2 per second
It also lacks specificity so O2 competes with CO2 to bind to it
Its active site is not specific
O2 attaches to RuBP to form glycolate so the plant has to go through photorespiration
At what kind of temperature is the more oxygen then CO2?
High
What does photorespiration do?
Protects photosynthetic apparatus from photoinhibition
Consumes O2 and releases CO2 (dark respiration)
Yields no ATP or NADPH
As much as 50% of the fuxed carbon might be reoxidize though
Remove phosphoglycolate
Why is photorespiration necessary?
When Rubisco evolved, there was little to no oxygen
Now 21% of air is oxygen and only 390 parts per million CO2
When does photorespiration happen?
When the temperature is high
The stomata is closed to conserve water
No supply of CO2 O2 is produced by photosynthesis and accumulates
Plants are growing in proximity
