Chapter 20: Calvin Cycle and Pentose Phosphate Pathway Flashcards
Write out mechanism of Rubisco
On ipad.
Describe how ATP and NADPH are used to convert 3PG to GAP.
ATP changes Ru5P to Ru1,5bP and it also is required for 3PG to change to 1,3bPG.
NADPH is required to go from 1,3bPG to GAP.
(Know the equation and this will be easier to answer).
Describe how 5 molecules of GAP are used to regenerate the initial 3 molecules of
Ribulose-5-phosphate, to keep the cycle going.
Draw the cycle.
Know the fate of the 6th GAP molecule.
The 6th GAP molecule is used for glucose synthesis. For every one glucose molecule there has to be two GAP molecules.
Describe the oxygenase activity of RUBISCO.
The oxygenase activity of rubisco is allowed to happen because CO2 is a linear molecule and so is O2. They are shaped similarly so the process works for both. When oxygen enters rubisco it goes through a different mechanism than CO2. O2 will end up making one 3PG molecule and a 2-phosphoglycolate. The 2-phosphoglycolate is then made into glycine.
Two glycine molecules can produce a serine molecule. Serine can then be made into another 3PG molecule.
This proves to be a problem. Photorespiration does the exact opposite of what the calvin cycle wants (fixation of CO2). It actually releases a CO2 molecule and it is also wasteful of energy.
The use of the C4 pathway is therefore worth the energy lost to not use photorespiration.
Describe the C-4 photosynthetic pathway, including why it is favored in some
environments.
The purpose of the C4 pathway is to prevent photorespiration. It uses two types of cells: Mesophyll and Bundle Sheath.
Mesophyll is more in contact with the air and the stroma. Bundle sheath cells are where photosynthesis and the calvin cycle occur.
In mesophyll cells:
Pyruvate–> PEP (+CO2)–> Oxaloacetate–> malate
The malate is then taken inside a bundle sheath cell where CO2 is released and malate turns into pyruvate.
This increases CO2 concentration in the bundle sheath cells where rubisco resides which prevents photorespiration occur less often. This process happens in the tropics because the rate of photorespiration increases faster as the temperature increases (faster than the rate of CO2 fixation).
Describe the regulation of the Calvin Cycle.
Some of the calvin cycle enzymes are activated by an increase in:
1.) pH (less [H+])
2.) [Mg2+] in stroma* (explain more about this one)
3.) reduced Fd concentration (can reduce thioredoxin and then reduce ATP synthase).
4.) [NADPH]
Know the three purposes of the Pentose Phosphate Pathway.
1.) Make NADPH for reductive biosynthesis.
2.) Make ribose sugars.
3.) Protect against reactive oxygen species (NADPH).
Know which steps generate NADPH.
G6P to 6-phosphoglucono delta lactone and also 6-phosphogluconate to Ru5P. Both of these reactions generate NADPH.
Know how three Ru-5-P are converted to two F-6-P and one GAP
This is the nonoxidative portion of the pentose phosphate pathway.
Describe how Pentose Phosphate, glycolysis, and gluconeogenesis all function under the
four metabolic situations
If we need much more ribose than NADPH:
-We can run glycolysis to make F-6-P and GAP, then run reverse reactions of PPP to make ribose.
If we need NADPH and Ribose is equal amounts:
-We can run the PPP normally.
If we need much more NADPH than ribose:
-we can run the oxidative portion of the PPP to make both, convert the ribose to F-6-P and GAP and then run gluconeogenesis.
If we need NADPH and ATP:
-We run the PPP, then convert F-6-P and GAP to pyruvate through glycolysis.
Explain how G-6-P dehydrogenase plays a role in protection of reactive oxygen species
There is NADPH produced in this step of the PPP. Glutathione is a small molecule that helps to reduce ROS. G-6-P is required to maintain reduced glutathione levels to protect against oxidative stress.
Explain how a deficiency in G-6-P dehydrogenase leads to hemolytic anemia
Cells with reduced levels of this enzyme are especially susceptible to oxidative stress.
In a liver cell, if the enzyme breaks down, more can be made. Liver cells have DNA/nuclei so mRNA can be made and then translated to produce more.
In a red blood cell, if the enzyme breaks down it cannot make more. They do not have a nucleus or DNA to make more. Without the protection from the enzyme/ protection from the ROS, the red blood cells will lyse (hemolysis).
Certain molecules can also produce ROS which puts more oxidative stress on the RBCs and can also induce hemolysis in those with this deficiency. (Primaquine, and fava beans).
Describe the regulation of the Pentose Phosphate pathway
Glucose-6-phosphate dehydrogenase as well as large amounts of NADPH and Ribose
