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Reading Guide, Stryer Short Course, Chapter 19
1. Use the citric acid cycle worksheet to help in learning the citric acid cycle.
2. The citric acid cycle is a series of redox reaction that ultimately converts the acetyl group of
acetyl CoA into _________________. In other words, the function of the citric acid cycle is the
harvesting of _____________________ from carbon fuels.
3. Notice that the citric acid cycle itself does not generate much ____________ nor include
__________ as a substrate. Instead, it captures high energy electrons to form ______________,
which are eventually oxidized.
4. In the first step, _________________ and _______________ react to form the 6-carbon
compound, citrate. In essence, it is the hydrolysis of the __________________ that makes this
reaction irreversible.
5. In the first step, _____________________ prevents an undesireable side reaction.
6. Citrate is isomerized to isocitrate to enable the 6-carbon unit to undergo
_____________________________.
7. In step 3, oxidation of the fuel leads to reduction of _____________ to ____________. This is
made irreversible by the loss of _________ gas.
8. Step 4 is also an oxidative decarboxylation, but because it is decarboxylation of an -ketoacid,
it requires the cofactor ______________________.
9. Stage two of the citric acid cycle is the regeneration of ____________________, which
involves two more oxidations and a substrate level phosphorylation.
10. The free energy of succinyl CoA hydrolysis is used to power formation of ___________.
11. In the mechanism of succinyl CoA synthetase, the high energy bond _____________ is
transformed into the high energy bond ____________________, which leads to phosphorylation
of the enzyme on a ____________ residue, then finally to formation of ___________.
12. Draw the three-reaction transformation of succinate to oxaloacetate. (You need to know this
basic pathway well because it shows up again.)
13. What is the energetic reason that FAD is used in some reaction rather than NAD+.
14. The net oxidation of an acetyl group has produced ___ CO2, ___ ATP, ___ NADH, and ___
FADH2.
15. Isotopic labeling studies show that the two carbons that enter the cycle are not the two that
_________________.
16. Details will be discussed in a later section, but oxidation of NADh can produce about ______
ATP. Oxidation of FADH2 result in formation of about _____ ATP. Therefore, one complete
turn of the citric acid cycle will produce about ______ ATP.
17. True or false: Glycolysis has both an aerobic and and anaerobic mode, whereas the citric acid
cycle is strictly aerobic.
18. The irreversible steps of the citric acid cycle are downregulated allosterically by ______,
which signals high energy charge, and _____ which signals a high reducing potential.
19. Inhibition of isocitrate DH leads to a buildup of _________________, which acts as an
inhibitor of the ____________________ pathway.
20. To understand the citric acid cycle, you must realize that, in addition to its role in the
production of ATP, it also provides __________________________________.
21. What problem would arise if oxaloacetate were converrted into glucose, then subsequently,
the energy needs of the cell arise?
22. What is the first step in gluconeogenesis? What role does it play in the citric acid cycle?
23. An _______________ reaction leads to the net synthesis or replenishment of pathway
components.
24. Most organisms cannot convert ______________ into net glucose.
25. In plants, the glyoxylate pathway allows for conversion of ___________________ into net
____________________. This pathway bypasses the two oxidative decarboxylation steps to
allow two acetyl CoA into the four carbon compound ________________.