Cellular Respiration & Fermentation (Chapter 9)

Make a flowchart indication the relationships among the four steps of cellular respiration. Which steps are responsible for glucose oxidation? Which produce the most ATP?

Glycolysis-pyruvate processing-TCA cycle-ETC. The first three steps are responsible for glucose oxidation; the final step produces the most ATP.

When do cells switch from cellular respiration to fermentation?

When electron acceptors required by the ETC are not available.

Where does the citric acid cycle occur in eukaryotes?

in the matrix of mitochondria

Why does aerobic respiration produce much more ATP than anaerobic respiration?

Aerobic respiration is much more productive because oxygen has extremely high electronegativty compared to other electron acceptors, resulting in a greater release of energy during electron transport and more proton pumping.

The presence of many sac like cristae results in a large amount of membrane inside mitochondria. Suppose that some mitochondria had few cristae. How would their output of ATP compare with that of mitochondria with many cristae? Explain your answer.

Because mitochondria with few cristae would have fewer electron transport chains and ATP synthase molecules, they would produce much less ATP than mitochondria with numerous cristae.

Compare and contrast substrate-level phosphorylation and oxidative phosphorylation.

Both processes produce ATP from ADP and Pi, but substrate level phosphorylation occurs when enzymes remove a "high-energy" phosphate from a substrate and directly transfer it to ADP, while oxidative phosphorylation is based on electrons moving through and ETC and production of a proton-motive force that drives ATP synthase.

What does the chemiosmotic hypothesis claim?

Electron transport chains generate ATP indirectly, by the creation of a proton-motive force.

Explain the relationship between electron transport and oxidative phosphorylation. What does ATP synthase look like, and how does it work?

Electron transport makes oxidative phosphorylation possible (oxidative phosphorylation occurs when electrons have been transported through the ETC and a proton gradient has been established). ATP synthase consists of an F0 unit and F1 unit joined by a stalk. When protons flow through the F0 unit, the stalk and F1 unit spin. The motion drives the synthesis of ATP from ADP and Pi.

Explain why NADH and FADH2 are called electron carriers. Where do these molecules get electrons, and where do they deliver them? In eukaryotes, what molecule do these electrons reduce?

NADH and FADH2 get their electrons from the intermediates of glycolysis, pyruvate processing, and the TCA cycle and deliver them to the ETC, where they reduce 02.

Describe what would happen to NADH levels in a cell in the first few seconds after a drug has poisoned the enzyme that converts acetyl CoA to citrate.

NADH would decrease if a drug poisoned the acetyl CoA to citrate enzyme, but increase if a drug poisoned ATP synthase.

Explain why organisms that produce ATP via fermentation grow much more slowly than organisms that produce ATP via cellular respiration.

Organisms that produce ATP by fermentation grow more slowly than those that produce ATP via cellular respiration simply because fermentation produces fewer ATP molecules per glucose molecule than cellular respiration does.

Explain why the addition of phosphate groups raises the potential energy of proteins, and why phosphorylation often causes proteins to change shape.

Phosphorylation adds two negative charges in a small area. The electrical repulsion that results raises the protein's potential energy and its tertiary structure.

Describe the relationship among carbohydrate metabolism, the catabolism of proteins and fats, and anabolic pathways.

Stored carbohydrates can be broken down into glucose that enters they glycolytic pathway. If carbohydrates are absent, products from fat and protein catabolism can be used to fuel cellular respiration or fermentation. If ATP is plentiful, anabolic reactions use intermediates of the glycolytic pathway and the TCA cycle to synthesize carbohydrates, fats and proteins.

Explain why cellular respiration produces so much more ATP per mole of glucose than fermentation, in terms of the total free-energy changes involved.

The free energy drop from glucose to oxygen (or another electron acceptor, during cellular respiration) is much greater that the free energy drop from glucose to pyruvate (during fermentation). Thus there is more free energy available to use in synthesizing ATP.

Most agricultural societies have come up with ways to ferment the sugars in barly, wheat, rice, corn or grapes to produce alcoholic beverages. Historians argue that this was an effective way for farmers to preserve the chemical energy in grains and fruits in a form that would not be eaten by rats or spoiled by bacteria or fungi. Why does a great deal of chemical energy remain in the products of fermentation pathways?

The potential energy drop between glucose and pyruvate is relatively small. When pyruvate acts as the electron acceptor during fermentation, a great deal of potential energy remains in the alcohol or other fermentation products.

Why are NADH and FADH2 said to have "reducing power"?

They donate electrons to components to the ETC, reducing those components.

Cyanide blocks complex IV of the electron transport chain. Suggest a hypothesis for what happens to the ETC when complex IV stops working. Your hypothesis should explain why cyanide poisoning in humans is fatal.

When complex IV is blocked, electrons can no longer be transferred to oxygen, the final acceptor, and cellular respiration stops. Fermentation could keep glycolysis going, but it is inefficient and unlikely to fuel a cell's energy needs over the long term. Cells that lack the enzymes required for fermentation would die first.

When yeast cells are placed into low oxygen environments, the mitochondria in the cells become reduced in size and number. Suggest an explanation for this observation.

When oxygen is unavailable for cellular respiration, yeast cells switch to fermentation, which occurs in the cytosol. They are unlikely to expend large amounts of energy and materials to maintain mitochondria.

Where does glycolysis occur in eukaryotes?

in the cytosol

Where does the electron transport and oxidative phosphorylation occur?

in the inner membranes of the mitochondria

What is the function of the reactions in a fermentation pathway?

to generate NAD+ from NADH, so glycolysis can continue.

When does feedback inhibition occur?

when an enzyme that is active early in a metabolic pathway is inhibited by a product of the pathway.