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.

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)

2. Which description is correct? (A) Every turn of a-helix is 3.6 Å in length. (B) Hydrogen bond in a-helix formed between residue i and i+3. (C) Heparin is glycosaminoglycan. (D) Collagen is full of a-helix structure and has Gly-X-Pro repeating sequence. (E) Orthologous genes are presumed to have been derived by gene duplication followed by gradual changes in the sequences of both copies.

複選題3. Which description is correct? (A) Glycogen is a homopolysaccharide form of glucose. (B) The galactose unit of the compound Gal(ẞ1→4) Glc residue is at the reducing end. (C) Starch is the most abundant polysaccharide in nature. (D) Gly residues are particularly abundant in a-keratin. (E) All amino acids in proteins are L-amino acids.

4. In the following enzyme reaction scheme, what sort of multi-enzyme kinetics are shown? (A) Ordered substrate binding with random product release. (B) Ordered substrate binding with ordered product release. (C) Random substrate binding with ordered product release. (D) Random substrate binding with random product release. (E) Ping-pong mechanism.