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.

19. RNAi methodology uses double-stranded pieces of RNA to trigger breakdown of a specific mRNA or inhibit its translation. For which of the following might this technique be useful? (A) to destroy an unwanted allele in a homozygous individual (B) to decrease the concentration of a desired protein (C) to form a knockout organism that will not pass the deleted sequence to its progeny (D) to decrease the production from a harmful mutated gene (E) to facilitate a specific gene be transcribed and translated.

20. Okazaki fragments are _____. (A) short stretches of DNA formed on the lagging strand (B) short RNA primers needed for initiation of polymerization (C) the smallest subunits of DNA polymerase III (D) fragments of DNA polymerase I that lack 5'→3' exonuclease activity (E) the non-specific side products of cellular DNA replication detected in eukaryotic nucleus

複選題21. Which property of DNA is (are) crucial for the conservation of genetic information? (A) the amount of A is the same as the amount of T (B) base-pair complementarity (C) the ability to form a circular DNA (D) semiconservative replication (E) antiparallelism

22. 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.

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.