ch. 8 oxygen crisis oppportunity Flashcards
Which enzyme catalyzes the capture of CO2 from the atmosphere in the Calvin cycle?
rubisco: enzyme that collects carbon from CO2 and sends in 2 PGA’s into reverse glycolysis
What is the advantage of the Calvin cycle over the reverse Krebs cycle (Why is it more efficient)?
Calvin cycle improved the efficiency of photosynthesis production of glucose. Enzymes in glycolysis don’t have to go both ways when carbon fixation is by the Calvin cycle. Enxymes are good at one thing and one thing only and because fewer enzymes have to go back and forth, it increases the overall efficiency because going back and forth makes them not as good at their jobs
What great advantage did the evolution of oxygenic photosynthesis give to cells?
it allowed photosynthesis to occur anywhere there was water and light, which is good because water is everywhere
What are the two disadvantages of H2O-splitting photosynthesis, one inconvenient, the other deadly?
inconvienient: oxygen in every water molecule is so electron hungry, the energy level of the electron stripped from water is significantly lower than that of an electron stripped from H2S. This causes electrons to not have enough energy to reduce NAD+ or other cofactors that are critical for reducing powers (CO2–>CnH2nOn) isn’t provided
deadly: oxygen atoms are very electron hungry. As a result, O2 gas tends to form a pair of exceedingly reactive ions (“free radicals”) that wreak havoc on unprotected cells by stealing electrons from covalent bonds and thereby altering covalent chemical structures
What remarkable revolution was caused by the accumulation of oxygen in the atmosphere?
The development of the electron transport carrier (ETC) with electron carriers and oxygen as the last electron acceptor in which oxygen’s electron hunger can be exploited to convert reducing power into ATP; A cell is now able to convert reducing power from NADPH into ejected protons (& thus indirectly ATP), by using the same electron carriers, but without light
The electron transport chain (ETC) really brought cellular life during the night-time into the fast lane.
a. What is the one direct function of the ETC?
b. Where does the ETC get its electrons?
c. How many total ATPs can be generated from the oxidative breakdown of one molecule of glucose?
d. How does this compare to the anaerobic breakdown of the same glucose?
a. ETC can eject a large # of protons for every electron that passes down the chain, creating a higher concentration outside of the cell (concentration gradient), so that it can power the proton pump in reverse making ATP using the reducing power from NADH and FADH2
b. NADH and FADH2
c. 29 ATPs
d. it’s a 15-fold increase over what glycolysis can make in the absence of oxygen (2 ATP net gain)
Draw a sketch (as usual, include all inputs and where they come from, and all outputs and where they go) to help you explain how the electron transport chain (ETC) really brought cellular life into the fast lane.
c. What is the name of the last electron carrier in the ETC?
d. What does it do with its electron?
c. cytochrome C
d. reduce 2H++.5O2 to H2O
Describe the big picture of Krebs cycle in the modern aerobic world. What are its reactants and where do they come from? What are its products and where do they go?
Glycolysis creates pyruvate needed to run Krebs cycle forward. Krebs takes pyruvate and converts ADP+Pi to ATP and takes NAD+ &FAD+ and converts it to NADH & FADH2 to make reducing powers needed
input: pyruvate (from glycolysis), ADP+Pi (from running cell), NAD+&FAD+ (from ETC)
output: CO2 (to environment), ATP (to running cell), NADH&FADH2 (to ETC)
Name the most important output of the modern Krebs cycle in the aerobic world. Explain why this output is so important.
reducing power created by NADH and FADH2 because its needed to run the ETC in aerobic photosynthesis
Use sketches of the cell membrane oriented vertically (with reducing power as the vertical access) to help you describe how the Electron Transport Chain likely evolved. Take advantage of the handout given to you in class. Use the words, inside cell, outside cell,
reducing power chlorophyll, light, electron, electron donor, NADH, H2O, O2, protons, reverse proton pump.
DRAW IT
Describe the inconvenient disadvantage (not the toxic one) of oxygenic photosynthesis.
The inconvienience of oxygenic photosynthesis is that it needs 2 light strikes since the energy level stripped from the electrons in H2O are significantly less than H2S due to oxygen being electron hungry. This prevents NADP+ and other cofactors from being reduced, in which there is a critical need for their reducing powers. Therefore, the cell had to evolve an additional chlorophyll molecule to take another photon from the sun so it could eject more energy into the low energy electron through the electron carrier. Then, at the electron carrier, H+ ions are pumped out, giving the reducing powers needed.
Be able to draw the sketch of sulfurogenic photosynthesis showing the membrane with reducing power on the vertical axis and explain the role of the following in the sketch: H2S, chlorophyll, electron carrier, NAD+, NADH, H+
Protons from light hits chlorophyll, which splits H2S into 2H++S+2e-. The 2e-‘s are then moved from the chlorophyll to an e- carrier. After, the e- carrier pushes an H+ ion from the inside of the cell to the outside of the cell. The e- carrier then delivers the 2e- to NAD+, which reduces it to NADH. The NADH then goes to glycolysis.
Be able to draw a sketch of oxygenic photosynthesis showing the membrane with reducing power in the vertical axis. Include and explain the role of the following in the sketch: H2O, chlorophyll, electron carrier, NADP+, NADPH, H+
Protons from the light strikes chlorophyll, which splits H2O into 2H++O+2e-. However, since e- from H2O don’t have enough energy, it has to start lower, so light has to strike twice. After light strikes (for both processs), 2e- from H2O splitting goes through chlorophyll to e- carrier, which then pushes out an H+ ion from inside of the cell to outside. After both light strikes, e- carrier then has a high enough energy electron to reduce NADP+ to NADPH. NADPH is then used to make glucose.
