複選題

27. 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.

複選題23. Here are two pieces of DNA, one with an adenine plus thymine content of 40%, and the other with a cytosine plus guanine content of 50%. If both are heated under the same experimental conditions, which of the following statement(s) about Tm of these DNAs is (are) correct? (A) The DNA with 40% adenine plus thymine will have the higher Tm. (B) The DNA with 50% adenine plus thymine will have the lower Tm. (C) The DNA with 50% cytosine plus guanine will have the higher Tm. (D) Their Tm's will be the same. (E) There's no way to predict for this information.

24. Which of following statements concerning RNA transcription is (are) false? (A) The template strand is read in the 3' → 5' direction. (B) The release of pyrophosphate from a nucleoside triphosphate drives the reaction. (C) Synthesis of RNA is a very accurate process. (D) Transcription requires the use of a primer. (E) RNA synthesis begins at the base in the DNA sequence designated as +1 (plus one).

複選題25. Which of the following general statement(s) about a G protein-coupled receptor is (are) true? (A) It contains seven transmembrane domains. (B) It is organized with the N-terminus on the cytoplasmic face of the membrane. (C) It is organized with the C-terminus on the cytoplasmic face of the membrane. (D) It uses trimeric G proteins, in which GTP binds to the γ subunit, to transduce signals in cells. (E) It uses small GTPase proteins to regulate cell division and cell motility.

26. Which of following statements describes a difference between replication of DNA and transcription of RNA? (A) Nucleoside triphosphates are the precursors for replication, but nucleoside diphosphates are used for transcription. (B) Both strands of DNA are copied in replication, but only one is copied in transcription. (C) Base pairing is used to copy the sequence in replication, but not in transcription. (D) The chain grows from the 5' to the 3' end in replication, but 3' to 5' in transcription. (E) RNA Primers are required for replication, but not for transcription.

複選題28. 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.

29. 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.

30. 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31. Proteins give cells structure and perform most cellular tasks, thus functions of proteins could be regulated via several different ways. Which of the following descriptions about regulating protein function are CORRECT? (A) Proteins are regulated at the level of synthesis, degradation or the intrinsic activity. (B) Proteins are marked for degradation with ubiquitin tag and then degraded within proteasomes or lysosomes. (C) Ubiquitination of proteins is irreversible. (D) Phosphorylation and dephosphorylation covalently regulate protein activity. (E) Protein activity could be regulated by controlling protein location and concentration.

32. Upon adding more NaCl into a protein solution, the electrostatic interaction between charged groups on the protein surface will be (A) strengthened due to ion exchange. (B) strengthened due to charge induction effect. (C) weakened due to charge induction effect. (D) weakened due to shielding effect. (E) will not be effected.

複選題33. Once transcription is finished and the primary RNA transcript is produced, it must undergo various processing reactions to yield functional RNAs. Which of the following descriptions about pre-mRNA processing are CORRECT? (A) In eukaryotic cells, pre-mRNAs are processed by 5' capping, 3' cleavage, polyadenylation and splicing in the cytoplasm. (B) Spliceosome is a large ribonucleoprotein complex catalyzing two transesterification reactions that joint two exons and remove the intron as a lariat structure. (C) Translation can be repressed by micro RNAs (miRNAs), which form imperfect hybrids with sequences in the 3' untranslated region (UTR) of specific target mRNAs. (D) RNA interference, which probably evolved as an early defense system against viruses and transposons, leads to degradation of mRNAs that form perfect hybrids with short interfering RNAs (siRNAs). (E) Many mRNA are transported to specific subcellular location by sequence-specific DNA-binding protein thus permit production of proteins at specific regions.