20. A monoclonal antibody differs from a polyclonal antibody in that monoclonal antibodies_______.
(A) are labeled with chemicals that can be visualized
(B) are produced by cells from the same organism that produced the antigen
(C) are synthesized by a population of identical, or “cloned” cells
(D) are synthesized only in living organisms
(E) have only a single polypeptide chain that can recognize an antigen 

16. The following techniques could be potentially employed as a tool in gene therapy except_______ . (A) RNAi (B) Antisense DNA (C) Triplex DNA (D) Ribozyme (E) DNA bending 

17. In glycoproteins, the carbohydrate moiety is always attached through the amino acid residues_______. (A) tryptophan, aspartate or cysteine (B) asparagine, serine or threonine (C) glycine, alanine or aspartate (D) aspartate or glutamate (E) glutamine or arginine

18. Sphingosine is not a component of_______. (A) cardiolipin (B) ceramide (C) cerebrosides (D) gangliosides (E) sphingomyelin

19. The ion channel that opens in response to acetylcholine is an example of a ____________ signal transduction system. (A) G protein (B) ligand-gated (C) receptor-enzyme (D) serpentine receptor (E) voltage-gated

21. Below is a diagram of two DNA strands that are part of the coding region of gene. What is the sequence of bases and strand orientation in the transcribed RNA molecular?5’ --- GTACGTGAA---3’ coding strand3’ --- CATGCACTT---5’ template strand (A) 3’ GUACGUGAA 5’ (B) 5’ GTACGTGAA 3’ (C) 3’ CAUGCACUU 5’ (D) 5’ CAUGCACUU 3’ (E) 5’ GUACGUGAA 3’

22. The human genetic disease phenylketonuria (PKU) can result from_______ . (A) lack of phenylalanine decarboxylase (B) deficiency in aromatic amino acid transaminase (C) a deficiency of protein in the diet (D) overproduction of ketone bodies (E) lack of an enzyme required for converting phenylalanine to tyrosine

23. Which of the following descriptions is not correct? (A) The leucine zipper motif is important for protein-DNA interaction. (B) Ribozymes are RNA molecules with catalytic activity. (C) The poly( A ) tail can stimulate recruitment of the 40s ribosomal subunit to mRNA； therefore, it is important in initiation of protein synthesis. (D) Diphtheria toxin can inhibit mammalian RNA synthesis by reduction the elongation factor-2 activity. (E) The suppressor tRNA molecules are capable of suppressing missense mutations.

24. “The knock-out mice” is an important animal model for biomedical research. One of the most important techniques involving in this transgenic animal’s establishment is_______ . (A) receptor expression in embryonic stem cell (B) gene targeting by homologous recombination (C) gene amplification in embryonic fibroblast cell (D) technique of chromosome walking (E) single nucleotide polymorphism analysis

25. If a sample of DNA is found to have the base composition (molar ratios) of adenine, 40； thymine, 22； guanine, 19 and cytosine, 19, what conclusion can be drawn? (A) The DNA is a circular duplex. (B) The DNA is a linear duplex. (C) The DNA is single stranded. (D) The DNA has highly repetitive sequences. (E) The DNA has a high melting temperature.

26. Which of the following statements concerning cyclins is not correct? (A) They catalyze the phosphorylation of cyclin-dependent protein kinases. (B) They are regulatory subunits for enzymes that catalyze the phosphorylation of proteins. (C) They are activated and degraded during the cell cycle. (D) They can become linked to ubiquitin. (E) They contain specific amino acid sequences that target them for proteolysis.