14. The GTP bound to ẞ-tubulin hydrolyzes to GDP and Pi ______.
(A) during formation of the α-β dimer
(B) during polymerization of dimers onto microtubules
(C) following polymerization but before depolymerization
(D) during depolymerization of dimers from microtubules
(E) following depolymerization of dimers from microtubules

10. Which of the following is not a contiguous membrane domain? (A) Rough ER (B) Nuclear envelope (C) Smooth ER (D) Transitional ER (E) Secretory granules

11. Most higher eukaryotic plasma membrane proteins are synthesized on ______. (A) free ribosomes and inserted after translation into the plasma membrane (B) ribosomes associated with the plasma membrane and inserted into the membrane cotranslationally (C) smooth ER and carried to the plasma membrane by vesicles that pinch off from the Golgi apparatus (D) rough ER ribosomes and carried to the plasma membrane by vesicles that pinch off from the rough ER (E) rough ER ribosomes and carried to the plasma membrane by vesicles that pinch off from the Golgi apparatus.

12. Most mitochondrial proteins are synthesized on ______. (A) mitochondrial ribosomes from nuclear mRNAs (B) mitochondrial ribosomes from mitochondrial mRNAS (C) cytoplasmic ribosomes from mitochondrial mRNAs (D) cytoplasmic ribosomes; they are imported after they are completely synthesized (E) cytoplasmic ribosomes; they are imported cotranslationally as they are being synthesized

13. Electron transport and oxidative phosphorylation are performed by protein complexes in the mitochondrial ______. (A) inner membrane (B) outer membrane (C) intermembrane space (D) matrix (E) Both a and c

15. Intermediate filaments function in ______. (A) cell motility (B) providing mechanical strength for cells (C) nuclear pore structure (D) All of the above (E) None of the above

16. Active transport is transport ______. (A) of all molecules simultaneously, against their concentration gradients, across the membrane (B) in an energetically favorable direction coupled to the hydrolysis of ATP (C) in an energetically unfavorable direction always driven by hydrolysis of ATP (D) in an energetically unfavorable direction always coupled to another reaction or source of energy (E) in an energetically unfavorable direction driven only by the flow of another molecule across a membrane

17. The function of gap junctions is to ______. (A) hold epithelia together (B) seal the space between cells (C) provide direct communication between cells (D) All of the above (E) None of the above

18. Protein kinase A is activated by ______. (A) binding of cAMP to its catalytic subunits (B) binding of cAMP to its regulatory subunits (C) phosphorylation of its catalytic subunit (D) phosphorylation of its regulatory subunits (E) binding of G protein subunits to its regulatory subunits

19. Nuclear envelope breakdown occurs at the _ of _. (A) end; prometaphase (B) end; metaphase (C) beginning; anaphase (D) beginning; prophase (E) end; prophase

20. A proto-oncogene is a gene ______. (A) from a normal cell from which an oncogene can arise (B) that has been picked up by an oncogenic virus (C) that is in the process of evolving into an oncogene (D) that is expressed abnormally in a tumor cell (E) that has been mutated to alter cell growth control