The number of calories used during physical exercise is greater than the number of calories used for the movements themselves. This may be caused in part by exercise-induced expression of uncoupling protein 1 (UCP1) in subcutaneous fat. Subcutaneous fat is mostly white fat cells but can also contain brown fat cells in mice and humans. As part of a thermogenesis program, UCP1 directly reduces the proton gradient driving oxidative phosphorylation. UCP1 expression is a characteristic of brown fat cells only and is induced by the protein irisin. The data in Table 1 address the relationship between exercise and: expression of UCP1 in subcutaneous fat cells, • expression of FNDC5 (a transmembrane protein in skeletal muscle plasma membranes), ● • blood levels of irisin (a soluble protein formed by cleaving the extracellular domain of FNDC5), and • expression of adiponectin (a hormone produced by white fat cells) in both wild-type mice and mice with overexpression of skeletal muscle PGC-1a (a transcription factor whose expression in skeletal muscle is induced by exercise). Table 1 Experimental conditions Effects of Exercise and PGC-1a on UCP1, FNDC5, Irisin, and Adiponectin Wild-type mice Mice with skeletal muscle PGC-1a Figure 1 Blood glucose (mg/dL) no endurance exercise 300- 250- 200+ 150- 100+ 50- 0₁ endurance exercise no endurance exercise Figure 1 shows the physiological effects of injecting viruses that encode either FNDC5 or a control protein into obese mice with disrupted glucose homeostasis. — FNDC5 UCP1 FNDC5 mRNA mRNA levels levels 80 nd overexpression Note: nd not determined; all measurements are relative to control. Protein encoded by virus control protein 0 1 25 O A. transformation. O B. transduction. O C. contamination. O D. conjugation. 2.5 Adapted from P. Bostrom et al. ©2012 Nature. 30 60 90 120 Time (min) FNDC5 effects on nonfasting blood glucose levels (Note: * indicates p < 0.05.) Mice that overexpress PGC-1a specifically in their skeletal muscles are most likely to exhibit which phenotype relative to wild-type mice? O A. Lower body weight O B. Lower body temperature O C. Higher physical activity O D. Higher nonfasting blood glucose levels 1 2.8 The viruses that encode either FNDC5 or control protein transfer genetic material via: Blood irisin levels 1 1.7 UCP1 most likely reduces the activity of which enzyme? O A. ATP synthase O B. Pyruvate kinase OC. Na+ K+ ATPase O D. Succinyl-CoA synthetase