Biology 1002B Lecture 5: Cycle 5 Outcomes
13 Jun 2018
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Lecture 10 Outcomes
Change in respiration rate (oxygen consumption) in isolated mitochondria by addition
of NADH, ADP, uncoupler etc.
- Addition of NADH favours the forward reaction (production of ATP) therefore more oxygen
will be consumed in the oxidative phosphorylation process
- The rate of oxygen consumption by mitochondria increases when ADP is added and then
returns to its initial value when the added ADP has been converted into ATP (because if ATP
synthase doesn’t have a substrate, it slows down the whole process, so it doesn’t accumulate
too much, and make the concentration gradient too big)
- Uncouplers carry protons across the inner mitochondrial membrane. In the presence of these
uncouplers, ATP is not formed by mitochondrial ATP synthase because the proton gradient
across the inner mitochondrial membrane is decreased (H+ don’t need to go through ATP
Synthase to get to the lower concentration) loss of respiratory control leads to increased
oxygen consumption and oxidation of NADH (because cell will need to pump more H+ to
compensate for the loss in the gradient)
Definition of respiratory control and how it is accomplished (proton gradient).
- there must be a substrate for the protons to make a proton gradient and move accordingly
- if the proton gradient gets too big, it restricts the rate of respiration (it gets harder and harder
to pump protons)
- if ATP synthase doesn’t have a substrate, it slows down the whole process, so it doesn’t
accumulate too much
Metabolic link(s) between chloroplast and
mitochondria.
- both organelles synthesize ATP
- G3P is removed from the calvin cycle using
energy from ATP and the reducing power of
NADPH and is exported to produce pyruvate
which is essential to produce Acetyl-CoA for
the Citric Acid cycle
- G3P is also an intermediate in glycolysis to
produce Acetyl-CoA by pyruvate oxidation
- G3P to make lipids, Nucleotides, amino acids,
pigments (biosynthetic rxns) out of the Cs
- Citric Acid Cycle produces CO2, while Calvin
cycle uses it
Autotrophic growth versus heterotrophic growth
- Autophototrophic growth occurs when both the Calvin Cycle and the Citric Acid Cycle are
functional (links described above)
- Heterotrophic growth occurs in the dark or without the presence of a functioning
photosynthetic pathway (glucose isn’t produced within the cell)
Reasons why Chlamydomonas can grow as a heterotroph on certain reduced carbon
compounds - but not others.
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- Chlamy can’t metabolize glucose, because theres no glucose transporter on the plasma
membrane, therefore if the glucose is not produced via the photosynthetic pathways, glucose
cannot get into the cell
- Instead, Chlamy brings in acetate from its surroundings — acetate is easily converted to
acetyl CoA to be used for biosynthetic reactions (in the Citric Acid Cycle)
- However, Chlamy grows its fastest when both chloroplasts and mitochondria are functioning
because it is a mixotrophic organism
Lecture 11 Outcomes
How to measure carbon fixation in Chlamydomonas
- can measure the disappearance of CO2, or the appearance of oxygen
- use a CO2 analyzer to see the amount of CO2 consumed, under high light, the rate should go
up because photosynthesis is high & calvin cycle speed is high, lots of cells also means the
rate would go up
- therefore the CO2 fixation rate must be measured in terms of CO2 consumed per time per
cell
How one can distinguish between gas exchange in mitochondria from that taking place
in the chloroplast of a Chlamydomonas cell.
- CO2 is consumed in the chloroplast, and oxygen gas is produced which is then consumed in
the mitochondria
- Photosynthesis can be measured either by the disappearance of CO2 or appearance of
oxygen, & Oxidative Phosphorylation can be measured by the disappearance of oxygen or
appearance of CO2
Identify major parts of a light response curve for carbon fixation
What metabolic processes and external factors may influence the change in rate as a
function of light.
- the rate of carbon fixation in the dark will be negative (in mixotrophic cells like Chlamy)
because cellular respiration is still working therefore CO2 is being released
- at a certain light intensity the calvin cycle and photosynthesis start to kick in, and carbon
fixation will surpass the light compensation point, and the cell will begin to gain weight
- Within a certain range of light intensity, carbon fixation is light limited because the amount
of NADPH and ATP goes up linearly with light intensity (light is proportional to the amount of
NADPH and ATP produce)
- Once the light intensity reaches higher levels, carbon fixation becomes light saturated
(curve plateaus) because it has reached the capacity of the Calvin cycle (the max. ability for
the CC to deal with the substrate, & the max. speed rubisco can turn over CO2 (ex. doubled
amount of light, no change in CO2 fixation)
- Rate of respiration remains constant (at whatever the rate was in the dark) regardless of light
intensity and photosynthesis
Light compensation point
- the point at which the rate of which photosynthesis is bringing in CO2 (calvin cycle is fixing
CO2) is perfectly offset by the rate at which respiration is releasing CO2
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Change in respiration rate (oxygen consumption) in isolated mitochondria by addition of nadh, adp, uncoupler etc. Addition of nadh favours the forward reaction (production of atp) therefore more oxygen will be consumed in the oxidative phosphorylation process. Uncouplers carry protons across the inner mitochondrial membrane. In the presence of these uncouplers, atp is not formed by mitochondrial atp synthase because the proton gradient across the inner mitochondrial membrane is decreased (h+ don"t need to go through atp. Synthase to get to the lower concentration) loss of respiratory control leads to increased oxygen consumption and oxidation of nadh (because cell will need to pump more h+ to compensate for the loss in the gradient) Definition of respiratory control and how it is accomplished (proton gradient). There must be a substrate for the protons to make a proton gradient and move accordingly.
