Unformatted text preview: g best explains the principal mechanism by which the diversity of lymphocytes arises? (A) During the development of B lymphocytes, rearrangements of the DNA coding for the various domains of the antibody molecule occur. (B) During the development of B lymphocytes, different introns are spliced out of antibody mRNA’s. (C) mRNA’s for all 1015 types of antibodies are produced by each B lymphocyte; however, only one type of mRNA gets translated. (D) All 1015 types of antibodies are produced by each B lymphocyte; specific proteases degrade all but one type. (E) Different B lymphocytes carry different transcription activators, so that only one specific mRNA (and therefore, antibody) is produced by each lymphocyte. 35. Hybridization between mature mRNA and DNA can identify introns in eukaryotic genes. When mature mRNA produced by the insulin gene is hybridized with denatured chromosomal DNA, which of the following will most likely be observed? (A) No hybridization would occur under any conditions. (B) Hybridization of mRNA would occur with random sections of chromosomal DNA. (C) Hybridization of mRNA with DNA would occur in a continuous stretch that is equal to the length of the mRNA. (D) Hybridization of mRNA with DNA would occur but with many single-stranded loops of DNA. (E) Hybridization of mRNA with DNA would occur but with many single-stranded loops of mRNA. 36. In adult mammals, the primary site for the final stage of differentiation of T lymphocytes is the (A) (B) (C) (D) (E) spleen bone marrow bursa of Fabricius thymus liver 37. In the DNA sequence 5 CGA TCG GCT 3 , which of the following is considered a transitiontype mutation? (A) (B) (C) (D) (E)
5 5 5 5 5 CGA CCG GCT 3 CGA TGG CT 3 CGA TCG CCT 3 CGA TCG GCA 3 CGA UCG GCU 3 38. Artificially acquired passive immunity involves (A) vaccination with attenuated virus or bacteria (B) the transfer of antibodies, as from a mother to her fetus (C) the production of a cellular immune response or antibodies (D) antibody formation as a result of exposure to antigens in the environment (E) injection of preformed antibodies such as immunoglobulin 39. Which of the following is true concerning animal retroviruses? (A) They must replicate during the S phase of the cell cycle. (B) They require an RNA-dependent DNA polymerase. (C) They are nonenveloped viruses. (D) The virions have double-stranded RNA genomes. (E) Replication of their genome occurs entirely within the host nucleus. GO ON TO THE NEXT PAGE.
Unauthorized copying or reuse of any part of this page is illegal. 20 40. In Escherichia coli, the synthesis of tryptophan is controlled by the tryptophan operon that is repressed in the presence of excessive tryptophan. When a mutant strain that has lost the regulatory gene of the tryptophan operon is placed in a medium that contains all nutrients the cells need to grow except tryptophan, which of the following will occur? (A) The cells will continue to grow even though excess tryptophan is synthesized. (B) The cells will gro...
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