15. In RNA, the base is connected to which carbon of ribose in the nucleotide structure? A. 1 B.1' C. 2 D. 2' E. 5' 18. Which class of lipids are the main components of cell membranes? A. isoprenoids B. wax esters C. sphingolipids D. phospholipids E. none of these 23. The prosthetic group on sphingolipids are: A. amino acids B. a peptide C. carbohydrates D. a heme group E. zinc 26. The membrane spanning portions of transmembrane proteins are often composed of what type of supersecondary and/or 2° structures? A. beta-barels & alpha-helices B. Greek key & beta turns C. beta-barrels & Greek keys D. double helices and alpha-helices E. beta-meander and alpha-helices
