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Lecture 9

Biology 1002B Lecture Notes - Lecture 9: Carbon Fixation, P700, Competitive Inhibition

Course Code
BIOL 1002B
Tom Haffie

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Lecture 9: Saturation kinetics
Photosynthesis, enzymes, transport
Light energy is converted into usable energy by photosynthesis to form glucose by using CO2
and releasing oxygen. The cells need energy, so in cellular respiration will use the glucose to
generate ATP and uses O2 and release CO2
Measuring carbon fixation
o CO2 analyzer, (does CO2 go up or down)
o Lights, too see if the rate will change with lights
o CO2 fixation rate = micromole carbon/cell (or it could be per chlorophyll)/min
Light saturation curve (light response curve)
o In the dark, the CO2 fixation rate is negative, below zero, it represents the mitochondria
respiration, CO2 is released
Because mitochondria releases CO2 it does not consume it, thus it below zero
o Increasing the light intensity from dime light to room light, there is a steady linear
increase of carbon dioxide consumption, because the product of the light reaction, it
can feed the Calvin cycle, so that the Calvin cycle can turn faster and consume more
o The rate of Calvin cycle is directly related to the light, more NADPH more ATP, the rate
will go up
o Low light cannot produce a lot of NADPH and ATP so that the Calvin cycle will not turn
as fast,
o Room light will have higher rate of CO2 fixation than dark
o the rate will not increase non-stop, there is a maximum rate, does not matter if there
unlimited NADPH and ATP, the rate will still not increase because the enzyme in the
Calvin cycle are at their capacity
o Thus the rate will plateau (turnover rate of enzyme -> regenerate RuBP), in early from
dim to brighter light it is a linear relationship, it will plateau after outside light to full
o The thing that limits the rate of Calvin cycle is the regeneration of RuBP (rubisco)
Inhibition with oxygen
o Other factors that limits the rate of carbon fixation:
Limited CO2, because there might not be enough CO2, if gives the system more
CO2 then the rate might increase
o Homework, sketch the curves at home…….. (find the curves in the power point)
There is a saturation point, where the enzymes in Calvin cycle are working at their maximum
When above saturation, the cell will receive more light than it needed. The photosystems, P680
and P700 can be broken down so that the cell will not receive as much energy as before, thus it
can protect the cell from too much energy
Even though there is light, the plant is not growing because it is losing CO2 from the
mitochondrial respiration, the chloroplast does not fix more than the cell used
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