Carbohydrate Metabolism - Biochemistry

In a eukaryote, oxidative phosphorylation occurs in the mitochondria because this is where the cell is able to set up a proton gradient. However, prokaryotes do not have mitochondria - they have no membrane-bound organelles at all. Therefore, the proton gradient that drives ATP synthesis in oxidative phosphorylation is created across the cell membrane.

With the excess buildup of protons in the matrix, the only thing that will be inhibited is the generation of ATP by ATP synthase. The other processes in cellular respiration focus more on creation of high energy electron carriers, and therefore will continue as normal.

Predictably, a gain in oxygen is known as oxidation, while a loss of oxygen is reduction. Hydrogen follows the opposite pattern as oxidation: removing hydrogen is oxidation, while gaining hydrogen is reduction. Therefore, the correct answer is that removing hydrogens is considered oxidation.

In order to differentiate between oxidation and reduction in terms of electron transfer, it is helpful to remember the phrase "LEO the tiger says GER". A loss of electrons is oxidation, while a gain of electrons is reduction.

During oxidative phosphorylation, is created from the previously created and . All of the other choices describe other parts of cellular respiration. In glycolysis, glucose is oxidized to pyruvate. In both glycolysis and the Krebs cycle, substrate level phosphorylation occurs. Likewise, and are produced during glycolysis and the Krebs cycle, but not during oxidative phosphorylation, where these high energy electrons are passed down a series of membrane-bound enzymes to oxygen meanwhile protons are pumped into the intermembrane space of the mitochondria.

The conversion of succinate to fumarate is the only reaction that occurs outside of the normal Krebs cycle. Complex II of the electron transport chain has an enzyme known as succinate dehydrogenase. This enzyme is responsible for the conversion of succinate to fumarate. Fumarate is return to the cycle where it is then oxidized to malate continuing the cycle. Each of the other reactions of the Krebs cycle listed all occur in the inner mitochondrial matrix; whereas the conversion of succinate to fumarate occurs at the inner mitochondrial membrane.

To answer this question, it's important to have familiarity with the process of aerobic respiration.

In the first major pathway, glycolysis is split into two molecules of pyruvate through a series of reactions. Along the way, high-energy electron carriers are produced, along with ATP.

In the next major step, pyruvate is transferred into mitochondria, where it is decarboxylated into acetyl-CoA, with a concomitant production of NADH and carbon dioxide. Hence, this is a step that produces carbon dioxide. However, it is not found in the answer choices.

The third major component of aerobic respiration is the citric acid cycle. Here, the acetyl-CoA from the previous step is completely ripped apart to provide a great deal of energy. This huge amount of energy that is liberated is because the two carbon atoms that make up the acetyl group of acetyl-CoA become completely oxidized into two molecules of carbon dioxide. In terms of the energy liberated from the cycle, ATP along with a good deal of high-energy electron carriers are produced. This component of aerobic respiration is indeed a source of carbon dioxide.

Fermentation is an anaerobic pathway and is thus not the correct answer. Depending on the organism, carbon dioxide may or may not be produced.

Finally, aerobic respiration culminates in oxidative phosphorylation. Here, all of the high energy carriers from the previous steps are fed into the electron transport chain, resulting in the production of a great amount of ATP, the main energy currency of cells. In this final major step, it is oxygen gas that is produced, not carbon dioxide.

First, let's consider the half reactions involved to determine .

This overall reaction involves the donation of 2 electrons, so

is defined as . The reaction we drew earlier is shown below:

We can see that was oxidized and was reduced. Find .

is Faraday's constant, and is defined as:

Solve for

A positive Gibbs free energy implies that the process in question should be unfavorable under normal conditions. The only process listed that is unfavorable and requires an input of energy is the pumping of hydrogen ions into the intermembrane space. This occurs during the electron transport chain.

The phases of cellular respiration are glycolysis, pyruvate dehydrogenase complex, Krebs cycle, electron transport chain. Glycolysis produces a net total of 2 ATP, the Krebs cycle produces 1 GTP that is converted to ATP in another process, and the electron transport chain is where almost all of the ATP made in cellular respiration is formed. However, during the pyruvate dehydrogenase complex phase of cellular respiration, pyruvate is converted to acetyl-CoA as a preparation for the Krebs cycle, but no ATP is created.

First, we must realize that the first committed step is the first irreversible reaction of glycolysis that is unique to glycolysis (cannot lead to another process, such as the pentose phosphate pathway). This is the third step, in which fructose-6-phosphate is converted to fructose-1,6-bisphosphate (the correct answer).

Glucose is the beginning reactant of glycolysis, and pyruvate is the final product. Glucose-6-phosphate is the product of the first step of glycolysis overall, but not of the committed step.

In photosynthesis, light is absorbed in order to move electrons from water molecules to NADPH. The reduction of to NADPH is accompanied by the movement of protons across a membrane which sets up a gradient similar to that of oxidative phosphorylation. The protons eventually run through ATP synthase and ATP is formed.

During photosynthesis, the light phase is responsible for creating which the dark phase then consumes as a part of its process. In addition to is used in the dark phase as a high energy substrate to work properly.

Absorbing four photons by photosystem II creates one oxygen molecule, so absorbing 12 would produce 3 molecules of .

During photosynthesis, the dark phase follows the light phase. The light phase produces which, along with , is fed into the dark phase where it is consumed (becomes and ). If the light phase continues working, but the dark phase does not, the and created during the light phase will not be consumed. Thus, there will be a decrease in the level of and (the correct answer). The relative proportion of will actually increase.

Carbohydrate production is a result of the dark phase working properly, so their levels would decrease in this instance. The sensitivity of the chloroplast to light would not change.

All of the answer choices are steps in the Calvin cycle, but the only one that describes the first stage - fixation - is and ribulose 1,5-bisphosphate reacting to form 3-phosphoglycerate.

The stages of the Calvin cycle in the order that they occur are fixation, reduction, and then regeneration. While carboxylation does occur as a part of the first stage, it is not what defines that stage.

Despite the Calvin cycle's other name (light independent reactions), light is indirectly required for this process to function. All other choices are true of the Calvin cycle.

Conversion of 1,3-bisphosphoglycerate to 3-phosphoglycerate is mediated by phosphoglycerate kinase. Conversion of phosphoenolpyruvate to pyruvate is mediated by pyruvate. In both these reactions adenosine diphosphate (ADP) is converted to ATP via substrate level phosphorylation. Conversion of 2-phosphoglycerate to phosphoenolpyruvate, mediated by enolase, does not produce ATP.

As glucose is introduced into the glycolytic pathway, it is first phosphorylated to create glucose-6-phosphate. That will then be converted to fructose-6-phosphate via phosphoglucose isomerase. That product will then be phosphorylated once more via phosphofructokinase-1 to create fructose-1,6-bisphosphate. Glucose-1,6-bisphosphate is never an observed intermediate in glycolysis.