複選題

18. Which descriptions are correct for DNA replication.
(A) The specific sites at which DNA unwinding and initiation of replication occur are called origins of replication.
(B) The DNA replicated form a particular origin of the replication is a "replicaon".
(C) Replicator sequences include initiator binding sites and easily unwound DNA.
(D) Helicase loading is the first step in the initiation of replication in eukaryotes.
(E) Mammalian DNA replication is semiconservative.

14. The product of the p53 gene _____.(A) causes cells to reduce expression of genes involved in DNA repair (B) inhibits the cell cycle (C) allows cells to pass on mutations due to DNA damage (D) slows down the rate of DNA replication by interfering with the binding of DNA polymerase (E) locates at the ribosome to ensure RNA translation efficiency

複選題15. Which of the following statements describes the lysogenic cycle of lambda (λ) phage are not correct? (A) The phage DNA is copied and exits the cell as a phage. (B) Most of the prophage genes are activated by the product of a particular prophage gene. (C) The phage genome replicates along with the host genome. (D) After infection, the viral genes immediately turn the host cell into a lambda-producing factory, and the host cell then lyses. (E) The lysogenic lambda can be induced into lytic cycle.

16. Bacterial cells protect their own DNA from restriction enzymes (endonucleases) by _____.(A) using DNA ligase to seal the bacterial DNA into a closed circle (B) adding methyl groups to adenines and cytosines (C) adding histones to protect the double-stranded DNA (D) forming "sticky ends" of bacterial DNA to prevent the enzyme (endonuclease) from attaching. (E) mutation of their genomic sequences to encode alternative proteins.

17. What information is critical to the success of polymerase chain reaction (PCR) itself? (A) The sequence of restriction-enzyme recognition sites in the DNA to be amplified must be known. (B) The sequence of restriction-enzyme recognition sites in the DNA to be amplified and in the plasmid where the amplified DNA fragment will be cloned must be known. (C) The complete DNA sequence of the DNA to be amplified must be known. (D) The DNA sequence of the ends of the DNA to be amplified must be known. (E) Similar Tm of both primers in the reaction.

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.

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).