Glycolysis - MCAT Biological and Biochemical Foundations of Living Systems

Glycolysis is the first step of cellular respiration. It is responsible for the production of two ATP molecules, two pyruvate molecules, and two NADH molecules. Lactic acid is a byproduct of anaerobic respiration in skeletal muscle.

The correct answer is glycolysis. Fermentation is a pathway that requires anaerobic conditions to activate. The citric acid cycle and Krebs cycle are two terms for the same process, and require aerobic conditions to proceed. Glycolysis has pathways that account for situations both in the presence and absence of oxygen.

In glycolysis, four ATP molecules made from each unit of glucose, however, two ATP molecules are used during this process, so the net result of one round of glycolysis is two ATP molecules. These products are made via substrate-level phosphorylation, a process in which a phosphorylated molecule transfers its phosphate to ADP or GDP (producing ATP or GTP).

The other choices are incorrect. Three NADH2 and one FADH2 are made in one round of the Krebs cycle, not glycolysis. Glycolysis is an anaerobic process and takes place in the cytoplasm, not the mitochondria. Finally, pyruvate products do not necessarily have to enter the Krebs cycle—they can be metabolized anaerobically if insufficient oxygen is present.

In glycolysis, one glucose molecule and two NAD+ molecules yield two molecules of pyruvate, two molecules of ATP, and two molecules of NADH.

Acetyl CoA is formed from pyruvate at the beginning fo the Krebs cycle. GTP is a product of the Krebs cycle. Oxygen and glucose are both reactants in metabolic processes that are derived from external intake (respiration and digestion).

The first step of respiration is glycolysis. All of the steps of glycolysis take place in the cytosol of the cell; this allows prykarotes to perform glycolysis, as well as eukaryotes.

Once pyruvate is generated from glycolysis, it is transported to the mitochondria to complete the citric acid cycle. The electron transport chain, the final step of cellular respiration, is located on the inner mitochondrial membrane, and utilizes the proton gradient in the intermembrane space.

Erythrocytes (red blood cells) have no mitochondria, and thus cannot use oxidative phosphorylation to produce additional ATP from pyruvate derived from glycolysis.

Liver cells (hepatocytes), neurons, and muscle cells (myocytes) can derive some ATP from glycolysis, but then feed the resulting pyruvate into the Krebs cycle in the mitochondria for additional energy production.

The initial reactants for glycolysis are glucose, ATP, ADP, and NAD+. The final products are pyruvate, ATP, ADP, and NADH. To get from glucose to pyruvate, a number of enzymes are needed. While knowing the names of each enzyme is not usually necessary, it is important to have a general understanding of the glycolytic process. The first step is phosphorylation of the reactant glucose, which is accomplished by hexokinase in most cells, and by glucokinase in the liver and pancreas specifically. The resultant glucose-6-phosphate then continues through the remaining steps in glycolysis to produce pyruvate.

Glycolysis produces four total ATP molecules, but only produces two net ATP. The process requires an initial investment of two ATP to initiate the glycolysis pathway. By using two ATP and producing four, there is a net production of two ATP.

Glycolysis is an anaerobic process that occurs in the cytoplasm. In addition to making ATP, glycolysis also generates NADH, which goes to play a role in the electron transport chain.

The glycolysis reaction follows two step. The initiation requires the input of two ATP, which become converted to ADP. Later in the process, however, four ADP are required to produce four ATP products. ADP is consumed in a greater quantity than it is produced, eliminating it from the net products.

For the NADH produced during glycolysis to be used in the electron transport chain (ETC), the electrons have to be sent into the inner membrane of the mitochondria from the cytoplasm, since glycolysis takes place in the cytoplasm. When the NADH is sent inside, sometimes it skips over NADH dehydrogenase and goes directly to coenzyme Q. The NADH does not always skip over NADH dehydrogenase, but it depends on the shuttle it takes into the mitochondrial matrix. The two shuttles are malate-aspartate, which maximizes NADH's ATP production, and glycerol-3-phosphate, which oxidizes one molecule of NADH, resulting in a decrease in the number of protons pumped. The type of shuttle depends on the cell type. This results in fewer protons being pumped out of the mitochondrial matrix, and thus fewer ATP being formed.

Glycolysis is the only metabolic process of the choices listed that does not occur in the mitochondrion; it occurs in the cytoplasm. Citric acid cycle and Krebs cycle refer to the same process, which occurs in the mitochondrion.

The product of glycolysis is ATP, and each cycle gives a net of two ATP, thus if there were already high levels of ATP in the body, glycolysis would not have to occur as frequently since the body's energy demands are already being met. High levels of ATP would serve as an allosteric inhibitor.

Decreased ATP and increased glucose would increase the rate of glycolysis. Increased oxygen or fructose may indirectly increase the rate of glycolysis, depending on other cellular factors.

Glycolysis is the first step of cellular respiration. It is responsible for the production of two ATP molecules, two pyruvate molecules, and two NADH molecules. Lactic acid is a byproduct of anaerobic respiration in skeletal muscle.

The correct answer is glycolysis. Fermentation is a pathway that requires anaerobic conditions to activate. The citric acid cycle and Krebs cycle are two terms for the same process, and require aerobic conditions to proceed. Glycolysis has pathways that account for situations both in the presence and absence of oxygen.

In glycolysis, four ATP molecules made from each unit of glucose, however, two ATP molecules are used during this process, so the net result of one round of glycolysis is two ATP molecules. These products are made via substrate-level phosphorylation, a process in which a phosphorylated molecule transfers its phosphate to ADP or GDP (producing ATP or GTP).

The other choices are incorrect. Three NADH2 and one FADH2 are made in one round of the Krebs cycle, not glycolysis. Glycolysis is an anaerobic process and takes place in the cytoplasm, not the mitochondria. Finally, pyruvate products do not necessarily have to enter the Krebs cycle—they can be metabolized anaerobically if insufficient oxygen is present.

In glycolysis, one glucose molecule and two NAD+ molecules yield two molecules of pyruvate, two molecules of ATP, and two molecules of NADH.

Acetyl CoA is formed from pyruvate at the beginning fo the Krebs cycle. GTP is a product of the Krebs cycle. Oxygen and glucose are both reactants in metabolic processes that are derived from external intake (respiration and digestion).

The first step of respiration is glycolysis. All of the steps of glycolysis take place in the cytosol of the cell; this allows prykarotes to perform glycolysis, as well as eukaryotes.

Once pyruvate is generated from glycolysis, it is transported to the mitochondria to complete the citric acid cycle. The electron transport chain, the final step of cellular respiration, is located on the inner mitochondrial membrane, and utilizes the proton gradient in the intermembrane space.

Erythrocytes (red blood cells) have no mitochondria, and thus cannot use oxidative phosphorylation to produce additional ATP from pyruvate derived from glycolysis.

Liver cells (hepatocytes), neurons, and muscle cells (myocytes) can derive some ATP from glycolysis, but then feed the resulting pyruvate into the Krebs cycle in the mitochondria for additional energy production.

The initial reactants for glycolysis are glucose, ATP, ADP, and NAD+. The final products are pyruvate, ATP, ADP, and NADH. To get from glucose to pyruvate, a number of enzymes are needed. While knowing the names of each enzyme is not usually necessary, it is important to have a general understanding of the glycolytic process. The first step is phosphorylation of the reactant glucose, which is accomplished by hexokinase in most cells, and by glucokinase in the liver and pancreas specifically. The resultant glucose-6-phosphate then continues through the remaining steps in glycolysis to produce pyruvate.