An oxidoreductase catalyzes the transfer of electrons from one molecule to the other, usually using ; i.e., it is an enzyme that catalyzes a redox reaction. Trypsin cleaves peptide bonds. Hexokinase phosphorylates hexose sugars. Glucose 6-phosphatase hydrolyzes glucose 6-phosphate into a phosphate group and glucose. Aspartate amino-transferase catalyzes the transfer of an amino group between aspartate and glutamate. Lactate dehydrogenase interconverts pyruvate to lactate, and at the same time  and .

The pyruvate dehydrogenase complex catalyzes the following reaction:

Since it is product inhibited, acetyl-CoA will inhibit the complex. 

There are 3 enzymes in glycolysis that carry out irreversible reactions: phosphofructokinase-1 (PFK-1), hexokinase and pyruvate kinase. While phosphatases are used to reverse the reactions for PFK-1 and hexokinase, they are not used in reversing the pyruvate kinase reaction. 2 enzymes are needed to convert pyruvate back into phosphoenolpyruvate (PEP). First, pyruvate carboxylase converts pyruvate into oxaloacetate, and then PEP carboxykinase converts this into PEP.

Fructokinase catalyzes the reaction of fructose converting into fructose-1-phosphate. Glycogenin acts as a primer for glycogen synthesis, by polymerizing the first few molecules of glucose. Glycogen synthase converts glucose to glycogen. Phospholipase hydrolyzes phospholipids.

The process of glycogenesis is when glucose is converted into glycogen. This occurs in the muscle and the liver after food is consumed. Gluconeogenesis is the process where glucose is produced from non-carbohydrate precursors. Glycogenolysis is the breakdown of glycogen. Glycolysis is the breakdown of glucose into two molecules of pyruvate. The Krebs cycle does not generate glycogen or glucose, rather it produces high energy electrons to be carried to the electron transport chain for ATP production.

Glyconeogenesis occurs in the hepatic pathway when no glucose is available. The electron transport chain occurs during cellular respiration. Glycolysis is the break down of glucose, not the production of glycogen. The Krebs cycle and citric acid cycle are the same thing, and both are used to produce NADH and ATP.

The pentose phosphate pathway (PPP) is a metabolic pathway in cells that is used to generate NADPH and/or ribose-5-phosphate for use in the cell, depending on the cell's needs. NADPH is used primarily to provide reducing power for several biosynthetic reactions, but it also serves as a means to keep glutathione predominately in its reduced form in the cell. This, in turn, helps maintain a reducing environment within cells. Furthermore, ribose-5-phosphate is used as a major precursor for the synthesis of nucleotides.

NADH and FADH₂ are not produced by the PPP, but rather are produced by the oxidation of glucose via the aerobic respiration pathway. These two molecules are carriers of high-energy electrons, which are used to generate ATP via the electron transport chain.

Glutathione, as mentioned previously, is not produced by the PPP; however, it does use the NADPH produced by the PPP to maintain its reduced form within the cell, which, in turn, maintains a predominately reducing environment within the cell. 2,3-bisphosphoglycerate is an intermediate of glycolysis, not the PPP. One major function of 2,3-BPG is to bind hemoglobin and reduce its affinity for O₂. This allows red blood cells to have an easier time releasing O₂ to tissues that are in need of it.

Fructose-2,6-bisphosphate is not a product of the PPP. Rather, it is produced from a side reaction of the glycolytic intermediate fructose-6-phosphate. Fructose-2,6-bisphosphate serves as an allosteric regulator of the enzyme fructose-1,6-bisphosphatase, which is an important regulatory enzyme for glycolysis and gluconeogenesis. Hormones such as insulin and glucagon can stimulate cells to alter their concentration of fructose-2,6-bisphosphate, which in turn regulates the activity of glycolysis and gluconeogenesis. Glycerol-3-phosphate is also not produced from the PPP. Rather, it can be produced from the phosphorylation of glycerol or from the reduction of dihydroxyacetone phosphate, an intermediate of glycolysis. It is used as the backbone for the formation of triglycerides and phospholipids.

Acetoacetate and beta-hydroxybutyrate are both ketone bodies produced not by the PPP, but from the condensation of two molecules of acetyl-CoA plus additional modifications. Generally, when the body is in a fasting state and needs to reserve blood glucose levels, ketone bodies can be produced to act as an alternative energy source, thus allowing glucose to be mostly spared.

In order to linearize using a  linkage, there needs to be an unbound carbon on the 1 position. However, sucrose is a  linkage and doesn't have a carbon available to linearize in the 1 position. It isn't a reducing sugar and therefore cannot be linearized. All of the other sugars have their anomeric carbon located at the 1 position and all of them are reducing sugars that can be linearized. 

From the question stem, we're told that the enzyme phosphoglucomutase is responsible for interconverting two intermediate forms of glucose, both glucose-1-phosphate and glucose-6-phosphate. We're then asked to determine the most likely metabolic pathway that glucose-6-phosphate would be used for in a fasting individual.

First, it's important to remember that in an individual that is fasting, energy resources become more scarce. Therefore, the body tries to conserve as much energy as it can in this state. Furthermore, since the brain relies mostly on glucose for its metabolism, the body tries to keep a relatively stable level of glucose in the blood. As a result, many tissues in the body switch from using glucose to instead using other energy sources, such as fatty acids or ketone bodies. In order to help ensure that blood levels of glucose remain stable, the liver increases its rate of gluconeogenesis, which generates glucose from non-sugar substrates, such as pyruvic acid, certain amino acids, and glycerol. Therefore, we would expect glucose-6-phosphate to be funneled mostly into the gluconeogenesis pathway.

Even though glucose-6-phosphate can also be diverted to other pathways, such as glycolysis, glycerogenesis, or the pentose phosphate pathway, all of these pathways result in a net consumption of glucose. In a fasting state, this is the opposite of what we would want, since blood glucose levels need to be mostly stabilized in order to ensure that nervous tissue has an adequate supply.

From the question stem, we are told that glucose-6-phosphate dehydrogenase oxidized glucose into another compound, and also produces a molecule of NADPH in the process. In order to determine the way in which this enzyme is likely to be regulated, it's important to consider feedback mechanics.

Since this enzyme is producing NADPH when it is turned on, we would expect this product to negatively regulate the enzyme via feedback inhibition. Moreover, since we know that  is a reactant, we can correctly assume that having a high concentration of this will likely drive the reaction forward by turning the enzyme on. Thus,  would be expected to allosterically activate this enzyme. Furthermore, the question stem tells us nothing about the unphosphorylated forms of these cofactors, therefore we have no way of knowing how many NADH or  affects this enzyme, if they do at all.