During exercise, protein synthesis in muscle cells stops. After exercise, protein synthesis starts again and contributes to the growth of muscle caused by exercise. A study by Dreyer et al found that the protein 4E-BP1 is normally phosphorylated in muscle cells, but becomes dephosphorylated during exercise and phosphorylated again after exercise. The dephosphorylated form of 4E-BP1 can bind to elF4E to block its normal function. How might 4E-BP1 block protein synthesis during exercise? A. 4E-BP1 binding to elF4E prevents release factors from binding to the A site of the ribosome.
B. 4E-BP1 binding to elF4E blocks the function of EF-Tu.
C. 4E-BP1 binding to elF4E makes the ribosome too big to translocate along the mRNA
D. 4E-BP1 binding to elF4E prevents loading of the mRNA onto the ribosome.