Question 1

Aerobic respiration involves the transfer of many electrons from glucose to electron carriers such as NAD⁺ over a series of multiple steps.Ultimately though, it is the reaction of glucose with oxygen to generate carbon dioxide, water and energy.Why doesn't glucose react directly with oxygen in cells?

Accepted Answer

The direct reaction of oxygen with glucose would release a large amount of energy all at once, which would be extremely destructive to cells. Instead, aerobic respiration allows for the controlled release of energy in multiple steps. Oxygen serves as the final electron acceptor in this process, but electron carriers like NAD+ and FADH2 are needed to transfer the electrons in a manageable fashion. Additionally, oxygen and glucose are not necessarily localized in different subcellular compartments, and oxygen can indeed accept electrons (which is why it is a crucial component of the electron transport chain). However, the reaction of oxygen with glucose is not spontaneous and requires the input of energy to overcome the activation energy barrier.

Question 2

What is common to all of the oxidation reactions in the Krebs cycle?

Accepted Answer

All oxidation reactions in the Krebs cycle involve the loss of electrons from an organic molecule, which are transferred to an electron acceptor, such as NAD+ or FAD, resulting in their reduction.

Question 3

A biochemist wants to control the initial substrate-level phosphorylation that occurs in the tracheal cells of grasshoppers once glucose has crossed the plasma membrane.He has access to the following inhibitors: Rotenone - an electron transport chain inhibitor, Oligomycin - an ATP synthase inhibitor, and TLN-232, an inhibitor of glycolysis.Which inhibitor should he use to slow down initial substrate-level phosphorylation that occurs once glucose has crossed the plasma membrane?

Accepted Answer

TLN-232 is an inhibitor of glycolysis, which is the pathway that leads to initial substrate-level phosphorylation. Therefore, using TLN-232 would specifically target the process that the biochemist wants to control. Rotenone and Oligomycin, on the other hand, would both target other parts of the cellular respiration process and would not directly impact substrate-level phosphorylation in the tracheal cells of grasshoppers.

Question 4

To form NADH from NAD⁺, two electrons and a proton are removed from an organic molecule.What term best describes the reaction in which electrons and a proton are removed from an organic molecule?

Accepted Answer

Dehydrogenation is the process of removing hydrogen, which includes electrons and a proton, from an organic molecule.

Question 5

If citrate levels are high in the cell, but ATP levels are low, what do you think will happen in the cell?

Accepted Answer

The answer of If citrate levels are high in the...

Question 6

Cardiac muscle cells need to generate significant amounts of ATP to allow for constant contractile activity.As a result, they primarily depend upon beta-oxidation of fatty acids, which has a higher energy yield than the catabolism of glucose.What would be the ATP yield for beta-oxidation of a hypothetical 10-carbon fatty acid?

Accepted Answer

The beta-oxidation of a 10-carbon fatty acid involves 4 cycles of beta-oxidation, producing 5 acetyl-CoA, 4 NADH, and 4 FADH2. Each acetyl-CoA enters the citric acid cycle, yielding 10 ATP per acetyl-CoA (5 x 10 = 50 ATP). The 4 NADH and 4 FADH2 from beta-oxidation yield an additional 14 ATP (4 x 2.5 + 4 x 1.5 = 14 ATP). The total ATP yield is 50 + 14 = 64 ATP, but accounting for the initial activation cost of 2 ATP, the net yield is 62 ATP.

Question 7

What are the products of one turn of the Krebs cycle?

Accepted Answer

One turn of the Krebs cycle produces 2 CO₂, 3 NADH, 1 FADH₂, and 1 ATP.

Question 8

Why is the energy generated from the catabolism of sugars and other macromolecules ultimately harnessed to generate ATP?

Accepted Answer

ATP is the primary source of energy for endergonic reactions in the cell. The energy generated from the catabolism of sugars and other macromolecules is ultimately harnessed to generate ATP, which can then be used by the cell to drive endergonic reactions.

Question 9

Regardless of the electron or hydrogen acceptor used, one of the products of fermentation is always

Accepted Answer

Fermentation regenerates NAD⁺ from NADH, allowing glycolysis to continue producing ATP in the absence of oxygen.

Question 10

Arsenic poisoning can lead to organ failure and death.Though arsenic can inhibit or interfere with a number of cellular enzymes, arsenic poisoning is thought to be mainly due to indirect inhibition of enzymes involved in both pyruvate oxidation and the Krebs cycle.As a result, this compound must be able to enter which cellular compartment?

Accepted Answer

Arsenic must enter the mitochondrial matrix because this is where pyruvate oxidation and the Krebs cycle occur.

Question 11

The energy released in the mitochondrial electron transport chain is used to transport proteins into the.

Accepted Answer

The energy released in the mitochondrial electron transport chain is used to pump protons (H+ ions) from the mitochondrial matrix into the intermembrane space, creating a proton gradient that drives ATP synthesis.

Question 12

What happens to the oxygen that is used in cellular respiration?

Accepted Answer

In cellular respiration, oxygen acts as the final electron acceptor in the electron transport chain and is reduced to form water.

Question 13

When substrate-level phosphorylation occurs, it means that:

Accepted Answer

Substrate-level phosphorylation is a metabolic process in which ATP is formed by the direct transfer of a phosphate group from a substrate molecule to ADP. Therefore, choice C is the correct option in which ADP is converted into ATP by the addition of a phosphate group.

Question 14

In the reaction catalyzed by aconitase, the conversion of citrate to isocitrate is inhibited by fluoroacetate.Fluoroacetate is used as a pesticide.Why is this an effective pesticide?

Accepted Answer

Fluoroacetate is converted to fluorocitrate in the body, which inhibits aconitase in the Krebs cycle, disrupting energy production and leading to the accumulation of toxic intermediates.

Question 15

What is the net number of ATP generated directly during glycolysis per molecule of glucose?

Accepted Answer

The answer of What is the net number of ATP...

Question 16

If you take into account the amount of ATP generated by ATP synthase per molecule of NADH and per molecule of FADH₂ produced, and the number of ATP molecules produced by substrate-level phosphorylation, what is the predicted energy yield of the Krebs cycle, per molecule of glucose in eukaryotic cells?

Accepted Answer

The answer of If you take into account the amount...

Question 17

Glucose is not our only food source, nor the only one we can utilize in our bodies to generate energy.Other primary sources of energy include other sugars, proteins, and fats.What metabolic intermediate are fats primarily converted into?

Accepted Answer

Fats are primarily broken down into fatty acids, which are then converted into Acetyl-CoA through a process called beta-oxidation. Acetyl-CoA then enters the Krebs cycle to be used for energy production.

Question 18

Pyruvate oxidation in eukaryotic cells occurs in the ________.

Accepted Answer

Pyruvate oxidation occurs in the mitochondria of eukaryotic cells, where pyruvate is converted into acetyl-CoA before entering the citric acid cycle.

Question 19

The Krebs cycle occurs in the mitochondria.There are nine biochemical reactions involved in the Krebs cycle, and they are highly ordered.Select the correct order.(Note: These are abbreviated and do not show NAD, ADP, ATP, or FAD.)

Accepted Answer

The correct order of the Krebs cycle is: acetyl-CoA combines with oxaloacetate to form citrate, which is then converted to isocitrate, then to alpha-ketoglutarate, followed by succinyl-CoA, succinate, fumarate, malate, and finally regenerating oxaloacetate.

Question 20

As electrons move along the electron transport chain, they lose potential energy.How is the energy that is released used by the cell?

Accepted Answer

The energy released by the electrons moving along the electron transport chain is used to transport protons against their concentration gradient, creating a gradient of protons across the inner mitochondrial membrane. This gradient is then used by ATP synthase to generate ATP through oxidative phosphorylation.

Quiz 7: How Cells Harvest Energy