A researcher is studying the role of glucose metabolites in normal cellular function. A specific human cell type is incubated in glucose-rich media. Intracellular levels of glucose metabolizing enzymes, intermediate products, and generated ATP are measured. In these cells, glycolysis of a single glucose molecule always yields pyruvate but sometimes generates no net ATP. Which of the following cells is most likely being studied in this experiment?

Question

A researcher is studying the role of glucose metabolites in normal cellular function.  A specific human cell type is incubated in glucose-rich media.  Intracellular levels of glucose metabolizing enzymes, intermediate products, and generated ATP are measured.  In these cells, glycolysis of a single glucose molecule always yields pyruvate but sometimes generates no net ATP.  Which of the following cells is most likely being studied in this experiment?

Quizplus · Accepted Answer

11ec160b_36e2_d84b_9249_b107badfa52c_MD0001_00 Erythrocytes use glycolysis as the major pathway to generate energy as they do not have mitochondria and therefore cannot use the citric acid cycle. During normal glycolysis, ATP is generated when 1,3-BPG is converted to 3-phosphoglycerate by the enzyme phosphoglycerate kinase. However, erythrocytes can bypass this part of the pathway using bisphosphoglycerate mutase, an enzyme that converts 1,3-BPG to 2,3-BPG in a step that produces no ATP. 2,3-BPG is subsequently catabolized to 3-phosphoglycerate by bisphosphoglycerate phosphatase in a step that also yields no ATP. By generating 2,3-BPG rather than proceeding with regular glycolysis, erythrocytes sacrifice the net ATP gain achieved in normal glycolysis. The major function of erythrocytes is to carry hemoglobin-bound oxygen from the lungs to the peripheral tissues, and 2,3-BPG is a very important regulator of oxygen-hemoglobin binding. The conversion of 1,3-BPG to 2,3-BPG is increased in hypoxia and chronic anemia. 2,3-BPG allosterically decreases hemoglobin's affinity for oxygen. As a result, in the presence of lower blood oxygen concentrations, higher 2,3-BPG levels within erythrocytes enable increased oxygen delivery in the peripheral tissues. (Choices A, C, D, and E) The enzyme bisphosphoglycerate mutase is present in large amounts in erythrocytes. However, it is present in insignificant quantities in adipocytes, hepatocytes, neurons, and myocytes; this causes virtually negligible 2,3-BPG production in these cell types. Educational objective: 2,3-BPG decreases hemoglobin's affinity for oxygen. Therefore, in the presence of lower blood oxygen concentrations, higher 2,3-BPG levels within erythrocytes enable increased oxygen delivery in the peripheral tissues. 2,3-BPG is produced from 1,3-BPG by the enzyme bisphosphoglycerate mutase. This reaction bypasses an ATP-generating step of glycolysis, causing no net gain in ATP. __________ References: Dephosphorylation of 2,3-bisphosphoglycerate by MIPP expands the regulatory capacity of the Rapoport-Luebering glycolytic shunt. (http://www.ncbi.nlm.nih.gov/pubmed/18413611) The energy-less red blood cell is lost: erythrocyte enzyme abnormalities of glycolysis. (http://www.ncbi.nlm.nih.gov/pubmed/16051738)

A Researcher Is Studying the Role of Glucose Metabolites in Normal