複選題

35. Which of the following statement(s) about heterochromatin is (are) CORRECT?
(A) It is a region of condensed chromatin.
(B) It is a region without DNA replication.
(C) It is often simple sequence DNA.
(D) It is a dark-staining area of a chromosome.
(E) It is usually transcriptionally active.

31.There are 45 different kinds tRNA (anticodons) available to serve as amino acid carriers, but there are 64 mRNA codons. Why aren't the tRNA anticodons and mRNA codons equal in number? (A) The reason is that some tRNA anticodons can misread some of the mRNA codons, which creates a "wobble" in the tRNA anticodons that can be repaired by RNA repair enzymes. (B) The reason is that the third base pair on the mRNA codon allows some flexibility (wobble)； thus, some tRNA anticodons can recognize more than one mRNA codon. (C) The reason is that the third base pair on the tRNA allows some flexibility (wobble)； thus, some tRNA anticodons can recognize more than one mRNA codon. (D) The reason is that the tRNA has the flexibility to choose which mRNA codons are necessary for building the polypeptide chain. (E) This broader recognition occurs because of the nonstandard pairing between bases in the wobble position corresponding to the 3' base in the mRNA and the complementary 5′ base in the tRNA anticodon.

複選題32. Which of the following describe the general mechanism of DNA synthesis is (are) TRUE? (A) One strand is made 5' → 3', while the other strand is made 3' → 5' in short discontinuous segments. (B) The strands become separated during synthesis. (C) Synthesis occurs in one direction from the starting site of synthesis. (D) Synthesis of DNA is a very accurate process. (E) DNA is replicated by a semi-conservative mechanism.

33.A mutation that changes the recognition sequence for the restriction enzyme EcoRI from GAATTC to GATTTC is an example of a (A) restriction fragment length polymorphism (RFLP). (B) single nucleotide polymorphism (SNP). (C) simple sequence repeat (SSR). (D) genetic heterogeneity (E) none of the above

複選題34. Which of the following statement(s) about intracellular second messengers is (are) TRUE? (A) It is a substance that brings about a desired effect in a cell as a result of a hormone binding to its receptor on the cell surface. (B) It is a hormone that affects the DNA of the target cell. (C) It is a specialized form of mRNA. (D) Cyclic ATP can act as secondary messengers. (E) Ca2+ can function as a secondary messenger by controlling the flow of Ca2+ into the cells.

複選題36. The three dimensional structure of nucleic acids can include: (A) Supercoiling (B) Base stacking (C) beads on a string (D) Circular molecules (E) Hairpin loops.

37. You are studying the function of a recently identified gene in C. elegans. You have been performing genetic screens for several months in an attempt to isolate loss-of-function mutations in this gene, but unfortunately you have been unsuccessful. Your advisor suggests that you try another approach to eliminate gene function. Which of the following techniques would accomplish this goal? (A) Design a repressor to bind to the operon of this gene. (B) Use a histone deacetylase to induce a transcriptionally inactive state. (C) Use RNA interference to prevent mRNA translation. (D) Use a wild type strain and mutagenize it with a UV light. (E) Use antisense DNA to block RNA transcription.

複選題38. Which of the following statement(s) is (are) CORRECT? (A) The DNA polymerases in eukaryotes have similar functions to those found in bacteria, but they are not identical. (B) Thymine dimers are most often caused by ionizing radiation. (C) The primase on DNA Polymerase a can make RNA structures only. (D) Telomerase activity may decline with old age. (E) Nicked segments of single-stranded DNA are linked by DNA ligase.

複選題39. Which of the following statements concerning restriction endonucleases is (are) TRUE? (A) They protect bacterial cells from invasion by viruses (bacteriophages). (B) They attack RNA, not DNA. (C) They attack single-stranded sequences only. (D) They can produce "sticky ends". (E) They do not display sequence specificity in their site of attack.

40. When electrical current is applied during a gel electrophoresis procedure, the DNA fragments are separated by (A) electrical charge, positive on one side, negatives on the other. (B) the number of poly-A tails associated with each one. (C) their response to the staining chemicals used during the procedure. (D) the size of the fragments. (E) the enzyme binding activity sites.

1. Which of the following pairs of bonds can rotate within a peptide backbone and the torsion angle of the latter is assigned as psi angle? (A) (B)(C) (D)(E)