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					                               Cellular Respiration

Campbell et al. Biology. 8th ed., Chapter 9

Study hint: While working through this study guide, make a list of key terms in the right
margin. Usually, these terms are boldfaced in the study guides or they appear in the
referenced figures. Consult one of the glossaries if you are not sure of definitions.

0. Application

   1. Case study: What's wrong with Kristine?

      Burning legs;
      Low energy;
      High blood acidity;
      Fainting;
      Reversible blindness

   2. What happens to energy stores in starvation?
   3. How does arsenate poisoning work?
   4. Why do untrained muscles hurt after a vigorous workout?

I. Energy transfer: Redox, phosphorylation, and energy carriers

   5. Autotrophs, e.g., ______________, acquire energy from _________ in a process
      called_______________. They convert this energy to energy stored in
      ___________ ___________. When needed, they _____________ these to
      __________ and __________. In this process,
   6. Heterotrophs, e.g., ___________, acquire energy from ________________. In
      their digestive tract they break down ___________________ to _____________.
      The latter are then imported into cells and oxidized to CO2 and water. In this
      process, ADP is ________________ to ATP (Fig. 9.2).
   7. Which monomers (chapter 5) can be broken down to yield energy?
   8. Review the structure of ATP (Fig. 8.8).
   9. Review: Why is ATP such a good cellular energy currency?

   Two reaction types are commonly used by cells to transfer energy:
   phosphorylation and redox reactions.

   10. Distinguish between substrate level phosphorylation (Fig. 9.7 and 9.14) and
       oxidative phosphorylation. Note: In biochemistry the phosphate group is
       commonly represented by a P with a circle around it.
   11. Explain redox reactions (page 163 and Fig. 9.3). Mnemonic: OIL RIG: Oxidation
       is loss, reduction is gain.
   12. Which member of a redox pair has more energy?
   13. What is the overall formula of cellular respiration (page 164)?
   14. In this formula, what is the reducing/oxidizing agent?
   15. What Is reduced/oxidized?
   16. Oxidation of glucose is a multistep process. What are the advantages of
       breaking this process down in many steps?
   17. Which role does NAD + play (Fig. 9.4)?

Why you should have a diet rich in vitamins:

      NAD + is a coenzyme that humans derive from niacin, a vitamin B

Other energy carriers frequently used in metabolism:

      NADP+
      FAD+ derived from riboflavin, a vitamin B

II. The steps of aerobic respiration

   18. Energy harvest occurs in 3 steps in aerobes (Fig. 9.6). Name those steps. In the
       video that you will see in lab, 4 steps are mentioned, the forth step is “pyruvate
       oxdation”, after glycolysis.

A. Glycolysis (splitting of sugar) (Fig. 9.9)

is a 10 step process (metabolic pathway). Each step is catalyzed by a different enzyme.
When studying these ten reactions in detail, keep in mind what glycolysis is supposed to
achieve: split glucose into two 3-carbon molecules of pyruvate (the "do it yourself
glycolysis" exercise takes pyruvate a step further to lactate).

   19. What it the significance of phosphorylation in step 1? (Hint: even though the
       oxidation of glucose is spontaneous, it does not happen very fast without help)
   20. Why is it important that step 1 is practically irreversible?
   21. Step two is easily reversible - why does that not matter at this point?
   22. Phosphofructokinase, which catalyzes step 3, is a major regulatory allosteric
       enzyme - how does it work, what is its significance, suggest effectors and
       inhibitors (Fig. 9.21).
   23. In step 5 we end up with two interchangeable 3-carbon sugars, step 6 only uses
       glyceraldehyde phosphate. How does this happen and what is the advantage?
   24. How does arsenate poisoning work (see step 6 in fig. 9.9)
   25. Balance input and output of glycolysis . For this and the following input/output
       tables, please know where reactant come from and where products go. Think of
       the transfer of electrons (oxidation/dehydrogenation and
       reduction/hydrogenation) and phosphate groups (Fig. 9.8).
                    Input                                   Output

Sideline: Fermentation in anaerobes (pp. 177-179)

Anaerobes use glycolysis to get 2 moles of ATP per mole of glucose.
Hydrolysis of ATP to ADP in cells has a delta G of -10 to -14 kcal/mol
A glucose molecule contains -686 kcal/mol. So the efficiency is low: around 2%.

   26. What is the consequence of the low energy efficiency for anaerobes (or: why
       can’t anaerobic bacteria run a marathon?)
   27. Besides the low efficiency, which two additional problems occur?
   28. Distinguish between alcoholic and lactic acid fermentation (fig. 9.18)

                             Alcoholic fermentation        Lactic acid fermentation
Starting products
End product
Cells that do it

   29. What happens to the lactate generated by our muscle cells under anaerobic
   30. Why are cells of the nervous system the first cells to die from a lack of oxygen
       (three reasons)? Hint: Remember this answer for the Kristin question.

The aerobe solution
A. Glycolysis (cytosol)

B. Pyruvate oxidation in mitochondria (Fig. 9.10)

   31. Which agent is oxidized? Which agent is reduced? From where to where is
       energy transferred?
   32. Describe the three coupled reactions within the mitochondria (p. 170)
   33. What happens to Acetyl CoA if there is enough ATP (p. 180: Biosynthesis).

If the cell needs more ATP right then and there, Acetyl-CoA goes into

C. Citric acid (Krebs) cycle (Fig. 9.11-9.12))

The citric acid cycle consists of a series of enzyme-catalyzed steps, similar to glycolysis
- but this is cyclic. It happens in the mitochondria, not in the cytosol.

   34. What is oxidized? What is reduced?
   35. How many turns of the cycle does it take to complete the oxidation of one
       glucose molecule?
   36. How can the Citric Acid cycle intermediate citrate be used to regulate the rate of
       ATP synthesis? (Fig. 9.21).
   37. Tally input and output of the citric acid cycle.

                  Input                      Recycled                      Output

   38. After the Calvin cycle, glucose has been completely oxidized. Where is its
       energy now?

              Energy carrier (quantify)                  Produced in which process?
                                                  Citric Acid cycle (don’t forget pyruvate

       You see that we have not generated much ATP (our ultimate goal) yet. In the
       next step, oxidative phosphorylation, we will transfer the energy stored in our
       intermediate energy carriers, NADH and FADH2 to ATP.

D. Oxidative phosphorylation

   39. Last step happens parallel to the others. Be able to explain the process,

      respiratory (electron transport) chain (Fig. 9.16)
      proton-motive-force (p. 176)
      chemiosmosis by ATP synthase (fig. 9.14)

   40. The process of chemiosmosis should remind you of a process encountered in the
       membrane chapter. Which is it and what are similarities and differences?

   41. Again, let's tally the input and output.

                       INPUT                                    OUTPUT

Summary of cellular respiration

   42. What is oxidized? Is that an exergonic or endergonic reaction?
   43. What is reduced?
   44. What is that energy used for?
   45. Where does the energy for the endergonic synthesis of ATP come from?
   46. In which order are the energy carriers of the ETC arranged?
   47. How many ATP can be synthesized from the conversion o f NADH and FADH
       depends on many factors. E.g., the electrochemical gradient across the inner
       mitochondrial membrane might be used for other work then the synthesis of ATP
      NADH generated during Krebs cycle -> max _____ ATP
      NADH generated during glycolysis -> max ______ ATP
      FADH -> max ________ ATP

The final tally

   48. What is the maximum amount of ATP produced by aerobic respiration?
   49. Why is that maximum rarely realized?

Saving Kristine

   50. Which of Kristine's symptoms is related to today's lecture?
   51. What is your hypothesis concerning the cause of her symptoms?
   52. Any suggestions how to cure her?
   53. Why do mammals in cold environment produce less ATP per mole of glucose?
   54. Why do infants produce less ATP per mole of glucose?

More general

   55. In summary, in humans, there are four major pathways for glucose metabolism -
       which are they?
   56. What are the factors that determine which of the four is taken?
   57. Compare photosynthesis and cellular respiration.

Essay question

Explain how ATP is produced in the inner mitochondrial membrane with the help of the
respiratory chain.

Lingjuan Ma Lingjuan Ma