Chapter 9 - Part 2

Chemiosmosis

The process in which energy stored in the form of a hydrogen ion gradient across a membrane is used to drive cellular work such as the synthesis of ATP.

glycolysis occurs in the cytosol and pyruvate oxidation, the citric acid cycle, and oxidative phosphorylation all occur in the mitochondrion.

Where do glycolysis, pyruvate oxidation, the citric acid cycle, and oxidative phosphorylation occur spatially?

Located in both the inner mitochondrial membrane and the mitochondrial matrix. Multiple reside in eukaryotic mitochondrial and chloroplast membranes and in prokaryotic plasma membranes.

Where is ATP synthase located?

If you keep adding more H+ ions, it becomes more acidic. enzymes are affected by the pH so a change in pH may result in the enzymes not being able to properly function.

Why is it important to have a compartment for the storage of H+ ions that is separate from the mitochondrial matrix? Hint: What happens to pH? Are enzymes affected by pH?

About 26 or 28 ATP. There is a variation dependent on which shuttle transports electrons from NADH in cytosol.

How much ATP is produced by oxidative phosphorylation? Why is there variation in the numbers (relates to shuttles)?

complex I, complex II, coenzyme Q (ubiquinone), complex III, cytochrome C, and complex IV.

1. What are the four protein complexes in the ETC?

This electron carrier is a small hydrophobic molecule, the only member of the electron transport chain that is not a protein. Is individually mobile within the membrane rather than reading in a particular complex.

2. Why is ubiquinone special?

The prosthetic group, called a heme group, has an iron atom that accepts and donate electrons. The last cytochrome of the chain, Cyt a3, passes its electrons to oxygen, which is very electronegative. Each oxygen atom also picks up a pair of hydrogen ions (protons) from the aqueous solution, neutralizing the -2 charge of the added electrons and forming water.

3. Why is Cytochrome c special (take a look at Fig. 9.15)

2H+ + ½ O → H2O The last electron carrier (Cyt a3) passes its electrons to oxygen, which is very electronegative.

4. What is the last reaction in the chain? Cyt a3 to Oxygen. This is the O2 as a reactant in the reaction C6H12O6 + O2 →Energy + CO2 + H2O. This is also the H2O in this reaction. This is why we need to breathe O2. The poison cyanide interferes with cytochrome oxidase which catalyzes this last reaction.

ATP Synthases

Are the only sites that provide a route through the membrane for H+. The passage of H+ through this uses exergonic flow of H+ to drive the phosphorylation of ADP. Makes ATP from ADP and inorganic phosphate. Use energy of the existing ion's gradient to power ATP synthesis.

NADH and FADH2 shuttle high energy electrons extracted from food during glycolysis and the citric acid cycle into an electron transport chain built into the inner mitochondrial membrane. The chain uses the exergonic flow of electrons from NADH and FADH2 to pump H+ across the membrane, from the mitochondrial matrix into the intermembrane space.

As electrons "fall" down the electron transport chain, what gets pumped into the inner mitochondrial membrane?

Similarities Fermentation, anaerobic respiration, and aerobic respiration are three alternative cellular pathways for producing ATp by harvesting the chemical energy of food. All three use glycolysis to oxidize glucose and other organic fuels to pyruvate, with a net product of 2 ATp by substrate-level phosphorylation. In all three pathways, NAD+ is the oxidizing agent that accepts electrons from food during glycolysis. Differences In fermentation, the final electron acceptor is an organic molecule such as pyruvate or acetaldehyde that oxidizes NADH back to NAD+. In cellular respiration, electrons carried by NADH are transferred to an electron transport chain, which generates the NAD required for glycolysis. Fermentation yields two molecules of ATp, produced by substrate-level phosphorylation. In absence of electron transport chain, energy stored in pyruvate is unavailable. In cellular respiration, however, private is completely oxidized in the mitochondrion. Most chemical energy is shuttled by NADH and FADHw in the form of electrons to the electron transport chain. Electron transport drives oxidative phosphorylation, yielding ATP.

Compare the efficiency of energy capture from glucose between these two types of anaerobic respiration compared with aerobic respiration.

NADH is oxidized to NAD+ and the regeneration of NAD+ creates ethanol and lactate from acetaldehyde and pyruvate.

For both alcoholic and lactic acid fermentation, what is the role of NADH? Does the organism extract energy from NADH?

10 H+

How many H+ are pumped into the inner mitochondrial membrane per NADH?

Having the electron transport chain, the mitochondrial matrix, and the inner membrane space close together, allows electron carriers to move shorter distances between each section allowing electrons to be transferred efficiently. - At certain steps along the chain, electron transfers cause H+ to be taken up and released into the surrounding solution. The electron carriers are spatially arranged in the inner mitochondrial membrane in such a way that H+ is accepted from the mitochondrial matrix and deposited in the intermembrane space.

Go back to Fig. 9.15. Study this figure. How are the spatial relationships between the electron transport chain, the mitochondrial matrix and inner membrane space key to their functions in cellular respiration?

H+ ions flowing down their gradient enter a channel in a stator, which is anchored in the membrane. H+ ions enter binding sites within a rotor, changing the shape of each subunit so that the rotor spins within the membrane. Each H+ ion makes one complete turn before leaving the rotor and passing through a second channel in the stator into the mitochondrial matrix. Spinning of the rotor causes an internal rod to spin. This rod extends like a stalk into the knowb below it, which is held stationary by part of the stator. Turning of the rod activates catalytic sites in the knob that produce ATP from ADP and P.

Go to Fig. 9.14. How does ATP synthase use the proton gradient (potential energy) to make ATP?

In the inner mitochondrial membrane

Go to Figure 9.15. Where is the electron transport chain located within cell?

As you move down the electron transport chain, the free energy decreases moving to each electron carrying molecule. The sequence of electron carriers in the electron transport chain drops in free energy as electrons travel down the chain.

How does the free energy (Y axis) change with each electron carrying molecule within the electron transport chain?

Cellular respiration harvest much more energy from each sugar molecule than fermentation can. Aerobic respiration yields up to 32 molecules of ATP per glucose molecule-up to 16 times as much as does fermentation.

How efficient is anaerobic compared with aerobic?

2 ATP are produced and 2 NADH are produced. ATP is produced through substrate-level phosphorylation.

How many ATP and NADH are produced through glycolysis? By what process is ATP produced?

2.5 ATP from one NADH. 1.5 from FADH2

How many ATP are estimated to be generated from one NADH? How much from a FADH2?

4 H+

How many H+ are needed to make one ATP?

Fermentation

In the absence of oxygen, many cells use this to porduce ATP by substrate-level phosphorylation. NAD+ is regenerated for use in glycolysis when pyruvate, the end product of glycolysis, serves as an electron acceptor for oxidizing NADH.

When oxygen is scarce, human muscle cells make ATP by lactic acid fermentation. This occurs during strenuous exercise, when sugar catabolism for ATP production outpaces the muscle's supply of oxygen from the blood. Under these conditions, the cells switch from aerobic respiration to lactic fermentation.

In thinking about long-distance runners, why might it have it be a good thing that we do lactic acid fermentation rather than alcoholic?

Yes

Is each transfer of two electrons from one electron carrier to the next within the electron transport chain a redox reaction?

Alcohol Fermentation

Pyruvate is converted to ethanol (ethyl alcohol) in two steps. Start with glucose and end with 2 of ethanol. CO2 waste product and 2 ATP produced. glucose → 2 pyruvate → 2 Acetaldehyde → 2 ethanol.

Lactic Acid Fermentation

Pyruvate is reduced directly by NADH to form lactate as an end product, regenerating NAD+ with no release of CO2

No because fats contain a high energy level of electrons, a gram of fat oxidized by respiration produces more than twice as much ATp as a gram of carbohydrate. This means that a person trying to lose weight must work hard to use up fat stored in the body because so many calories are stockpiled in each gram of fat.

Take a brief look at Fig 9.19. In addition to breaking carbohydrates down into glucose and breaking them down beginning with glycolysis, both proteins and fats have components that can enter and be broken down using the glycolysis, pyruvate oxidation, and the citric acid cycle. Also note that all the arrows should be reversible, so excess G3P and Acetyl CoA can be pulled out to make fat. Based on this, can someone who eats a diet low in fat, but high in carbohydrates or proteins still get fat? Why?

Take a brief look at Fig. 9.20. Note that phosphofructokinase is a key enzyme targeted for regulation in this pathway. Both citrate and ATP inhibit this enzyme (feedback inhibition). So high levels of these compounds result in a slowing of glycolysis. Under what conditions would you expect citrate and ATP to build up?

Take a brief look at Fig. 9.20. Note that phosphofructokinase is a key enzyme targeted for regulation in this pathway. Both citrate and ATP inhibit this enzyme (feedback inhibition). So high levels of these compounds result in a slowing of glycolysis. Under what conditions would you expect citrate and ATP to build up?

Collection of molecules embedded in the inner membrane of the mitochondrion in eukaryotic cells. Where electrons (from NADH or FADH2) move from a less electronegative electron carrier (one with a lower affinity for electrons) to a more electronegative electron carrier down the chain, releasing free energy.

Take a look at Figure 9.13. What is an electron transport chain again?

2 Acetyl CoA

What are "energy products" produced in pyruvate oxidation reactions?

They are moved through the electron transport chain and undergo chemiosmosis to produce ATP.

What happens to all the NADH/FADH2 produced in glycolysis, pyruvate oxidation, and citric acid cycle?

Electrons acquired from glucose by NAD+ during glycolysis and the citric acid cycle are transferred from NADH to the first molecule of the electron transport chain in complex I. This molecule is a flavoprotein, so named because it has a prosthetic group called flavin mononucleotide. The flavoprotein returns to its oxidized form as it passes electrons to an iron-sulfur protein. The iron-sulfur protein then passes the electrons to a compound called ubiquinone (electron carrier, small hydrophobic molecule) FADH2 adds its electrons from within complex II, at a lower energy level than NADH. NADH and FADH2 each donate an equivalent number of electrons (s) for oxygen reduction, the electron transport chain provides about one-third less energy for ATP synthesis when the electron donor is FADH2 rather than NADH.

What happens to the electrons from NADH? How about FADH2? In the electron transport chain

6 NADH, 2 FADH2. and 2 ATP. ATP is produced through substrate-level phosphorylation.

What is produced in the Citric Acid Cycle? How is ATP produced in glycolysis and citric acid cycle?

The electron transport hain provides about ⅓ less energy for ATP synthesis when the electron donor is FADH2 rather than NADH.

What is the energy difference between NADH vs. FADH2?