24. Which of the following sequential order for the secretory pathway is false?
(A) Rough endoplasmic reticulum (ER) → ER-to-Golgi transport vesicles → Golgi cisternae → secretory vesicles.
(B) Rough ER → ER-to-Golgi transport vesicles → Golgi cisternae → Mitochondria.
(C) Plasma membrane → Early endosome → Late endosome → Lysosome.
(D) Rough ER → ER-to-Golgi transport vesicles → Golgi cisternae → Late endosome → Lysosome.

20. Protein X contains seven transmembrane domains, with a short N-terminus and a long C-terminus. Following protein synthesis, the N-terminus of the protein faces the lumen (the inside) of the endoplasmic reticulum (ER). After protein X is transported to the cell surface via exocytosis, you would expect the C-terminus of the protein X to be (A) extracellular. (B) cytoplasmic. (C) in the lumen of ER. (D) in the lipid bilayer of the plasma membrane.

21. The genetic material of which kind of cells is included in a single, circular molecule of DNA? (A) bacteria (B) yeasts (C) flies (D) flowering plants

22. Kinases, which are responsible for the activation or inactivation of a number of proteins, can add phosphate groups onto (A) tryptophan residues. (B) tyrosine residues. (C) cysteine residues. (D) a and c. (E) none of the above

23. The dissociation constant (Ka) of the human serotonin receptor for serotonin is 1 x 10-10 M. What does this mean? (A) It means that when the concentration of the serotonin receptor is 1 x 10-10 M, half of the available serotonin receptor sites are occupied. (B) It means that when the concentration of the serotonin receptor is 1 x 10-10 M, all of the available serotonin receptor sites are occupied. (C) It means that when the concentration of serotonin is 1 x 10-10 M, all of the available serotonin receptor sites are occupied. (D) It means that when the concentration of serotonin is 1 x 10-10 M, half of the available serotonin receptor sites are occupied. (E) None of the above

25. The first step in the secretory pathway that should be inhibited by a dominant-negative mutant of SNARE proteins is (A) rough endoplasmic reticulum to Golgi transport. (B) intra Golgi transport. (C) trans Golgi network (TGN) transport to the plasma membrane. (D) TGN transport to the late endosome.

26. Which of the following statements about tRNA is correct? (A) There are 61 different types of tRNAs. (B) Stop codons are recognized by specialized tRNAs. (C) Aminoacyl-tRNA is formed by joining the amino group of an amino acid to a tRNA. (D) The amino acid residue, instead of the anticodon, determines the specificity of an aminoacyl-tRNA. (E) Each tRNA folds into a unique structure for codon recognition.

27. What is a Shine-Dalgarno sequence? (A) It is a pyrimidine-rich stretch. (B) It is complementary to the 3'-end of the 23S ribosomal RNA. (C) It is usually followed by a stop codon. (D) It usually forms a stem-loop structure. (E) It is located at the 5' UTR.

28. An enhancer (A) is a protein that binds to RNA polymerase and stimulates transcription. (B) is a metabolite that stimulates transcription of eukaryotic promoters. (C) interacts with repressor proteins to enhance transcriptional activity. (D) acts as a binding site for RNA polymerase. (E) none of the above.

29. Which of the following statements regarding RNA splicing is correct? (A) It is an important mechanism for translational regulation. (B) It usually occurs in both prokaryotes and eukaryotes. (C) It requires GTP, instead of ATP, as the energy source. (D) It may produce different mRNA sequences from the same gene. (E) None of the above.

30. Which of the following statements on ribosome is correct? (A) Its molecular weight is about 100 KDa. (B) The RNA component contributes more to the mass than does the protein component. (C) The catalytic core is consisted of proteins. (D) It hydrolyzes ATP during reaction. (E) None of the above