Starch is a complex carbohydrate that is digested by enzymes in the small intestine. These digestive enzymes, called glucosidases, are released by exocrine glands in humans and are involved in breakdown of complex carbohydrates to their individual monomers (glucose). Recall that energy production in cell begins with glycolysis, where a molecule of glucose is metabolized to produce intermediates for subsequent metabolic steps. Cells can’t use starch or glycogen during glycolysis; therefore, the student must add glucosidase to break down starch into individual glucose molecules.

Energy can be produced in anaerobic conditions (like in glycolysis). It might not have a high yield of energy such as aerobic respiration, but the cells can still produce energy when they are oxygen deficient. As mentioned, glycogen is a complex carbohydrate; therefore, adding it without glucosidase will not help facilitate energy production.

Anaerobic metabolism, such as glycolysis and fermentation, occur in the cellular cytoplasm. The products of glycolysis are transported to the mitochondria where they undergo Krebs cycle (in mitochondrial matrix) and oxidative phosphorylation (on the inner mitochondrial membrane). Both Krebs cycle and oxidative phosphorylation require oxygen and are, therefore, called aerobic metabolism.

Glycolysis is an anaerobic process that produces 2 net ATP, 2 pyruvate molecules, and 2 NADH. Pyruvate is a three-carbon molecule. Recall that glucose is a six-carbon molecule; therefore, the six-carbon glucose is broken down to two three-carbon pyruvate molecules. This means that all the carbons in glucose are transferred to the pyruvate molecules. ATP is produced and consumed in glycolysis. There is a total of four ATP molecules synthesized in the glycolysis; however, glycolysis consume two ATP molecules so you get a net of 2 ATP molecules. Finally, glycolysis involves the reduction two  molecules to yield two NADH molecules (not FAD).

The starting molecule in glycolysis is glucose, a six-carbon molecule while the ending molecule in glycolysis is pyruvate, a three-carbon molecule. During glycolysis glucose is split and its six carbons are used to make 2 molecules of three-carbon pyruvate because. Note that no carbon dioxide is released during glycolysis, but since aerobic metabolism (starting with the Krebs cycle) uses acetyl-CoA as a substrate, which is two carbons long, one molecule of carbon dioxide is released for each molecule of pyruvate produced during glycolysis.

Glycolysis is the first step in producing ATP. Glycolysis is an anaerobic process that occurs in every cell. Certain cells, such as red blood cells, only rely on glycolysis for energy. In most of the other cells, glycolysis produces ATP and few intermediates that will be used in subsequent steps to generate more ATP; therefore, glycolysis occurs in every cell.

The major input for glycolysis is glucose. Glycogen, a storage form of glucose, needs to be broken down into individual glucose units before undergoing glycolysis. The net products of glycolysis are 2 NADH, 2 pyruvate molecules, and 2 ATP. There is a total of 4 ATP produced in glycolysis; however, two of the ATP molecules are consumed, leaving behind only 2 net ATP.

The first step of glycolysis consumes a molecule of ATP, removing one of the phosphate groups to make ADP. This phosphate group is added to glucose to make Glucose-6-phosphate, therefore glucose is phosphorylated.

The correct answer is glyceraldehyde-3-phosphate dehydrogenase. This enzyme sequesters a hydrogen from carbon 4 on glyceraldehyde 3-phosphate to reduce  to , and in its place, an inorganic phosphate molecule is transferred to this position. Fructose-bisphosphate aldolase converts Fructose-1, 6-bisphosphate to glyceraldehyde-3-phosphate and dihydroxyacetone phosphate. Pyruvate kinase converts phosphoenolpyruvate to pyruvate whereas enolase converts 2-phosphoglycerate to phosphoenolpyruvate. Phosphoglycerate kinase converts 1, 3-bisphosphoglycerate to 3-phosphoglycerate. 

Thiamine is an important vitamin required for the conversion of pyruvate to acetyl-CoA. It is an important cofactor for the pyruvate dehydrogenase, an enzyme important for the conversion of pyruvate to acetyl-CoA. Pyruvate and NADH from glycolysis will continue to be produced; however, they cannot go any further without thiamine. This means that cells can’t undergo Krebs cycle and oxidative phosphorylation to produce ATP.

The buildup of pyruvate and NADH will cause the pyruvate molecules to undergo fermentation and produce lactic acid. It also will oxidize NADH, the product of which is essential for several cellular processes and needs to be regenerated.

The question states that the cell undergoes aerobic respiration. This means that the products from anaerobic respiration (glycolysis) will go through Krebs cycle and electron transport chain (aerobic respiration) to generate ATP. Lactate dehydrogenase is an enzyme important for converting the pyruvate molecules (from glycolysis) to lactate and oxidizing NADH. This reaction occurs in anaerobic fermentation when there is tissue hypoxia (decrease in oxygen).

If this inhibitor was placed in a cell that is deprived of oxygen, then there would be a buildup of pyruvate and NADH; however, since the inhibitor is added to cells undergoing aerobic respiration there will be no buildup. The pyruvate and NADH will undergo aerobic respiration and generate ATP. Note that red blood cells (RBCs) are unique in that they only use anaerobic respiration for ATP; therefore, adding lactate dehydrogenase inhibitor to RBCs will lead to a buildup of pyruvate and NADH.

Glycolysis has three irreversible enzymatic steps that help the substrate intermediates proceed in one direction through the glycolytic pathway: the enzymes are hexokinase, phosphofructokinase 1, and pyruvate kinase. Of these three enzymes, the most important enzyme that controls the rate of glycolysis is phosphofructokinase 1, or PFK-1. Pyruvate carboxylase is not used in glycolysis, but in gluconeogenesis.