19. Stem-cell populations are thought to exist in adult animals at which of the following organs?

(1) skin 

(2) intestine

(3) bone marrow
(A) all 3 organs
(B) (2)
(C) (3)
(D) (1) and (3)
(E) (2) and (3)

15. Why do cells not have membrane transport proteins for O2? (A) Because oxygen can dissolve in the lipid bilayer and diffuse in and out rapidly without the need for a transporter. (B) Because oxygen can dissolve in water and leak in via water channels. (C) Because they need to keep the oxygen concentration low inside the reducing environment of the cell. (D) Because oxygen transport across a membrane is energetically unfavorable. (E) Because oxygen is transported in and out of the cell in special oxygen-carrying proteins such as hemoglobin.

16. Which of the following is required for the transport of proteins into the nucleus? (A) Signal peptidase (B) Nuclear localization signal (C) Translocon complex (D) Ubiquitin tag (E) Endoplasmic reticulum targeting sequence

17. Which component is directly responsible for initiating translation in eukaryotic cells? (A) mRNA cap-binding proteins (B) Ribosomal small subunit (40S) (C) tRNA (D) Golgi apparatus (E) RNA polymerase II

複選題18. The lysosome is primarily responsible for degrading (A) Misfolded proteins in the cytosol (B) Proteins tagged with ubiquitin (C) Extracellular material taken up by endocytosis (D) Lipids synthesized in the endoplasmic reticulum (E) Ribosomal subunits

20. Which of the following statements regarding stem cells (SCs) is incorrect? (1) A stem cell can divide to one copy of itself and to one differentiated cell.  (2) Stem cells could be used to test new drugs. (3) The multipotent SCs showed higher differentiation potency than the pluripotent SCs. (A) (1) (B) (2) (C) (3) (D) (2) and (3) (E) (1) and (2)

21. Vesicular transport describes the budding and fusion behavior of vesicles. Which of the following statement(s) is   correct   regarding vesicular transport? (1) The vesicular transport process is ATP-dependent, as ATP is required for both the budding and fusion of vesicles. (2) COPI-coated vesicles are primarily involved in anterograde transport from the endoplasmic reticulum (ER) to the Golgi apparatus. (3) Dynamin is a GTPase that is responsible for the vesicle budding from the donor membrane during clathrin-mediated endocytosis. (A) 3 only (B) 1 and 3 (C) 2 and 3 (D) 1 and 2 (E) All of above are correct.

22. Membrane transport describes different ways for molecules to across the cell membrane. Which of the following statements is   correct   regarding membrane transport? (1) In facilitated diffusion, molecules move across the membrane through a protein channel or carrier down their concentration gradient. (2) The presence of aquaporins in the cell membrane facilitates the active transport of water molecules into and out of the cell. (3) Secondary active transport does not directly utilize ATP but relies on the electrochemical gradient created by primary active transport. (A) 3 only (B) 1 and 2 (C) 1 and 3 (D) 2 and 3 (E) All of above are correct.

23. Which of the following statement(s) is   correct   regarding ER-Golgi transport pathway? (1) The process of cisternal maturation suggests Golgi cisternae is used to replenish its resident enzymes without forming the vesicles. (2) The Rab GTPase proteins play a role in vesicular transport and in regulating the maturation of Golgi cisternae, coordinating their movement and fusion. (3) Signal sequence is responsible for targeting a protein to the ER membrane during translation. (A) 3 only (B) 1 and 2 (C) 1 and 3 (D) 2 and 3 (E) All of above are correct.

24. Which of the following statements about translesion DNA synthesis (TLS) is true? (A) It uses conventional DNA polymerase δ to replicate across lesions. (B) It is a repair mechanism for DNA breaks. (C) It prevents replication collapse by allowing specialized polymerases to bypass lesions. (D) It occurs only in prokaryotes, not in eukaryotes. (E) It strictly follows base-pairing rules without introducing mutations.

25. Which chromatography method would best separate proteins based on their isoelectric points (pI)? (A) Ion exchange chromatography (B) Gel filtration chromatography (C) Reverse-phase chromatography (D) Affinity chromatography (E) IMAC (Immobilized metal affinity chromatography)