BIOLOGY 103
     Chapter 6:  CELLULAR RESPIRATION

 

CELLULAR RESPIRATION
most important concept:  
ATP:  How does the cell transfer energy from food molecules to ATP?.

BIO 103 HOME PAGE

For Monday:  Overview & Glycolysis,  textbook pages  113-119

  • ATP fig. 6.1
    and pp. 113-4. 
    ATP supplies energy for almost all cellular processes, but making ATP or re-building it from ADP requires energy.  (You're supposed to know this already.) Throughout this chapter try to focus on these questions:    How does this step help the cell transfer energy from food molecules to ATP?   Where is the energy at the beginning of this step, and where is it at the end of this step?
  •  The redox reactions (pp. 114-6) emphasized in this chapter are basically the same idea as  exergonic reactions supplying energy for endergonic reactions (again, like what you're supposed to know already). 
    • Reduction is an endergonic process.  A reactant gains energy as it is converted into a reduced molecule.  The reduced product has more energy than the original reactant. 
       The energy is in the form of electrons.   In biochemical reactions, you can usually tell where the energetic electrons are going because an H goes with them. 
    •  Oxidation is basically an exergonic process.  The product which has become oxidized has lost free energy, electrons, and (usually) H.  Sometimes oxygen is what oxidizes the reactant but not always.  (The formation of water looks like a reduction of oxygen but it hardly counts because the electrons are at their lowest energy level when "bad O" shares them with "H.")
    • Overall is the metabolism of sugar an oxidation or a reduction? 
              C6H12O6 + 6O2 ---> 6H2O + 6CO2 
      If it's an oxidation, where has the energy gone?  If it's a reduction, where did it get new electrons?  A hint follows:  (NAD+/NADH)
    • NAD+/NADH (fig 6.2 )  pp. 115d-116:   In the detailed steps we'll be studying this week, many of the steps are redox reactions where electron energy is transferred from a fragment of sugar to a coenzyme molecule called NAD+.  When NAD+ is converted to NADH, has it become oxidized or reduced?  If it has been oxidized, what reduction reaction is involved?  If it has been reduced, how is it coupled to an oxidation?

  • The Overview, fig. 6.3 and pp. 116-117a, summarizes groups of reactions which will be repeated in diagrams through the rest of the chapter. If you can explain the overview and include a few extra details, you understand the most important information in this chapter.

    1. Glucose is the initial reactant.  Its carbons all eventually end up in CO2      -                         C6H12O6 + 6O2 ---> 6H2O + 6CO2 
    2. NADH (and another coenzyme, FADH2) transfer the electrons and hydrogen atoms released from glucose.   
    3. GLYCOLYSIS  is a series of reactions oxidizing glucose to pyruvate (pyruvic acid).   C6H12O6 ---> 2 C3H4O3 
      Glucose is an aldose sugar (CHO); pyruvate is a carboxylic acid (COOH); do you remember which has more energy?  If not, review your notes from chapter 2 and chapter 3.
    4. pyruvate  is oxidized and then combined with another acid to form citric acid  (=citrate)
    5. KREBS CYCLE (also called the citric acid cycle) is a series of reactions oxidizing organic acids to CO2
    6. The most important function of glycolysis and the Krebs cycle is to reduce coenzymes (NADH and FADH2), and they also produce a little ATP.  Most ATP is produced during .... 
    7. ET-OxPhos:  Electron Transport and oxidative phosphorylation (the last panel in fig. 6.3) is the only phase which uses O2  
      ET-OxPhos       produces the most important product....
    8. ATP is red to remind us how it's the most valuable product of all.  The energy to make ATP involves combining O2 with electrons and protons to make H2O.  Where does ET-OxPhos get its electrons and protons?
  • You should learn the eukaryotic locations for the three stages, suggested in 6.14 or this:  fig overview:
    • glycolysis:  cytoplasm
    • Krebs Cycle:  mitochondrial matrix (see fig. 6.8)
    • Electron Transport & OxPhos:   mitochondrial cristae
  • Eventually you will have to know the initial reactants and final products for each group.  If you pay attention to your textbook and your professor and really work on the rest of this chapter, you will begin to see patterns and it will all make sense. 
  • Figure 6-4 shows the details of glycolysis.   
    • The details are less  important than overview points #1, 2, 3, and 6 above.   
    • This animation has even more details (you don't need to learn all the molecules), and sometimes seeing the details helps you understand the big picture.
    • Regulation of glycolysis (pp. 117-8) involves material assigned for enzymes.  Review it now or repent later.  another version:  fig 6inhibit
  • CHECKLIST:  reduction-oxidation reactions (redox reactions), reducing agent, oxidizing agent, reduced, oxidized, ATP, NADH, FADH2, cellular respiration, aerobic respiration, glycolysis, phosphorylation, phosphofructokinase, pyruvate, Krebs cycle, citric acid cycle, tricarboxylic acid cycle, coenzyme, feedback inhibition (product inhibition), mitochondrial matrix, cristae, electron transport chain 
  • PREVIEW OF QUIZ & EXAM QUESTIONS:
  1. Overall through glycolysis (and the citric acid cycle), the number of atoms in the fragments of glucose
    [a] decreases.  [b] increases.    [c] remains the same.
  2. Overall through glycolysis (and the citric acid cycle), the energy in the fragments of glucose
    [a] decreases.  [b] increases.    [c] remains the same.
  3. Most reactions of glycolysis are
              [a] endergonic.   [b] exergonic.
  4. Overall during glycolysis, the fragments of glucose become
           [a] oxidized.   [b] reduced.
  5. Overall, what are the initial reactants of glycolysis?
  6. Overall, what are the final products of glycolysis?
  7. Of the ten reactions in glycolysis, how many require enzymes?
  8. How many of the ten reactions of glycolysis occur within the mitochondrion?
  9. What controls the rate of glycolysis?  fig 6inhibit.

If you are looking for the answers, you're not getting them here.   The point of these questions is to trick you into studying the textbook carefully.

For Wednesday:   Electron Transport Chain and other details

  • KREBS CYCLE DETAILS:  fig. 6.6,  pp. 118-122. 
     
    Study the details for understanding, but not memorization (you can look up these details in almost any science textbook). Try to focus on these questions:    How does this step help the cell transfer energy from food molecules to ATP?   Where is the energy at the beginning of this step, and where is it at the end of this step?  Be able to answer these questions:

    1. When oxygen is present, what happens to pyruvate?  (fig. 6.6c) Why? (fig. 6-3)
    2. Overall through the citric acid cycle (fig. 6-6), the number of atoms in the fragments of glucose
                [a] decreases.  [b] increases.    [c] remains the same.
    3. Overall through glycolysis and the Krebs cycle, the energy in the fragments of glucose
                [a] decreases.  [b] increases.    [c] remains the same.
    4. Of the eight reactions in the citric acid cycle, how many require enzymes?
    5. Of the eight reactions in the citric acid cycle, about how many oxidize a glucose fragment?
    6. Of the eight reactions in the citric acid cycle, how many reduce a NAD+ or a FAD?
    7. Of the eight reactions in the citric acid cycle, how many occur within a mitochondrion?
    8. Overall, what are the initial reactants of the citric acid cycle?
    9. Overall, what are the final products of the citric acid cycle?
    10. The overall message of this figure Krebs energy is that most of the big energy losses from the glucose fragments involve transfers to
            [a] ATP (via GTP).  [b] NAD or FAD.   [c] other fuel fragments.
    11.  Most of the reactions of the Krebs cycle are
                [a] endergonic.   [b] exergonic.
    12. Whenever NAD is reduced, what becomes oxidized?
            [a] ATP.  [b] NAD.   [c] glucose fragments
    13. Whenever ATP is produced in glycolysis or the Krebs cycle, what provides the energy?
            [a] ADP.  [b] NAD.   [c]  glucose fragments.
    14. How is Krebs Cycle regulation (fig. 6.7) like regulation of glycolysis (fig. 6.5)?
  •  
  • ET details. 
  • Begin with fig. 6.8, then 6.9, then Fig. 6.14.  Look at the upper right part. 
  • Then compare ET on fig. 6.14 and fig. 6.12 and fig. 6.10.
  •  
  • Here's the point:  As electrons move to lower and lower orbitals on the series between NAD and the other ET molecules, their excess energy is exploited to move protons into the cristae (intermembrane space).  
  • OxPhos details.  Begin with Fig. 6.14.  Look at the upper right part.  Then compare OxPhos from Fig 6.14 with Fig. 6.13c.  

    Here's the point:  As protons diffuse out of the cristae, they can move only through a channel in the enzyme ATP synthase.  The stream of protons works like a wind mill or water wheel, converting proton gradient energy to chemical energy stored in the bond connecting phosphate to ADP.  
  • ET & OxPhos Summary.  Begin with Fig. 6.14.  Scan the text pages 122b-127.  Details in the text are less important than being able to explain figure 6.14.   Make sure that you can answer these questions:
    1. What is a proton gradient?
    2. What creates the proton gradient?
    3. What is the important product of ATP-synthase enzyme (fig. 6-13a)?
    4. ATP ---> ADP + Pi       Is this reaction
          [a] endergonic.     or    [b] exergonic?
    5. ADP + Pi   --->   ATP          Is this reaction
          [a] endergonic.     or    [b] exergonic?
    6. Is the movement of protons from the crista to the matrix (ffig. 6-13a)
          [a] endergonic.     or    [b] exergonic?
    7. Is the movement of protons from the matrix to the crista (fig. 6-12)
          [a] endergonic.     or    [b] exergonic?
    8. The production of ATP is coupled with the movement of protons from the
      [a] crista to the matrix.   [b] matrix to the crista.
    9. The movement of electrons "down" the electron transport chain (fig. 6-12) is coupled with the movement of protons from the
      [a] crista to the matrix.   [b] matrix to the crista.
    10. Electrons are at their lowest energy level when they combine with
           [a] ATP.   [b] glucose.   [c] O2.   
    11. Overall, the initial reactants in ET/OxPhos are:
    12. Overall, the final products of ET/OxPhos are:
    13. The electron transport chain and oxidative phosphorylation.  What do these two names mean; how do the two names together almost explain what happens?
    14. Why don't the electron transport molecules produce ATP when they're in a test tube instead of in the cristae?
  •  
  • Fermentation / Anaerobic Respiration. 

    Fig. 6.15 has the most important details.  You could read p. 128 if you need it to answer these questions:  
    1. O2 is a reactant only in
        [a] the citric acid cycle.   [b] glycolysis.   [c] the electron transport chain.
    2. But without molecular oxygen and the products of the electron transport chain, the citric acid cycle is missing this critical initial reactant:
    3. So the citric acid cycle cannot work without the electron transport chain.  Then respiration must become
      [a] aerobic.   [b] anaerobic.
    4. When oxygen is present, what happens to pyruvate?  (fig. 6.6c) Why? (fig. 6-14)
    5. When oxygen is absent, what happens to human pyruvate? Figure lactate Why?
    6. When oxygen is absent, what happens to yeast pyruvate?  In yeast
  • Metabolic Pathways.  Fig. 6.16 and 6.17 and 6.18: 

    The text on pp. 129-130 is clear, and the essay on pp. 131-2 helps put everything into perspective.  The most important points are these:
    1. almost anything organic can be turned into a "glucose fragment" and then zapped in the Krebs cycle.
    2. Some human cells can metabolize only glucose, and all human cells "prefer" glucose or glycogen, its polymer.  Cells continuously hydrolyze old proteins and build new ones; and most human cells will use these hydrolyzed proteins (=____________) for energy if glucose levels are low.  A few human cells will "burn" fatty acids (via acetyl-CoA), but usually only if there's no other fuel available.  However, tissues will hydrolyze stored fats before they cannibalize proteins which are being used.
    3. When the Krebs cycle is "down-regulated," the interaction with other metabolic pathways usually sends excess acetyl-CoA directly to your hips.
    4. So, what are two possible fates of acetyl-CoA?  
    5. What factors do you think might control the fate of acetyl-CoA? 
    6. Alcoholics often have strange-looking mitochondria; can you hypothesize why?  
    7. Can you think of a hypothesis to explain why heavy drinkers also often have high levels of cholesterol?  
    8. What molecules (other than  glucose) can be oxidized by glycolysis?
    9. What molecules (other than  glucose) can be oxidized by the citric acid cycle?
    10. What happens when the cell has too much ATP?
  • SUMMARY:  Activity 6.1 Glucose Metabolism

  • CHECKLIST: reduction-oxidation reactions (redox reactions), reduced, oxidized, ATP, NADH, FADH2, aerobic respiration, ANaerobic respiration, glycolysis, phosphorylation, pyruvate, Krebs cycle, citric acid cycle, tricarboxylic acid cycle, coenzyme, acetyl CoA, oxaloacetate, citrate, feedback inhibition (product inhibition), cytochrome c; chemiosmotic hypothesis, proton-motive force, ATP synthase, substrate-level phosphorylation, oxidative phosphorylation, fermentation

  • PREVIEW OF QUIZ & EXAM QUESTIONS:
  1. "Altogether about 90 percent of the energy stored in the chemical bonds of a glucose molecule is converted to chemical energy in the form of the high-energy compounds, _________ and __________."   So where's the other 10%?
  2. Fig. 6-14  gives an overview of the major pathways. Go back to it now and find a study-buddy who will listen to you explain the details in it.
  3. How are cellular structures "designed" for their ATP-producing functions?   Which structures are involved and how?

If you are looking for the answers, you're still not getting them here.   The point of these questions is to trick you into studying the textbook carefully.


If you're addicted to tables, here you are:

  Glycolysis Krebs Cycle ET/OxP Fermentation
PURPOSE        
LOCATION   matrix cristae  
Initial Reactants   pyruvate (or acetyl), , NADH,  
Main Products pyruvate, NADH, a little ATP     a little ATP, lactate or ethanol, NAD+
WHATEVER else you think you should remember        

 

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