複選題

33. Which of the following features are true regarding tyrosine recombinases?
(A) They introduce double-strand breaks.
(B) They introduce Holliday junctions.
(C) They cleave all four DNA strands before strand exchange.
(D) They break and rejoin one pair of DNA strands at a time.
(E) They include the Cre recombinase that recognizes the loxP site.

29. Which of the following features is true regarding telomerase? (A) It carries its own DNA template. (B) It adds a repeat sequence to the 5' end of telomeres. (C) Its activity is high in somatic cells and low in most cancer cells. (D) It relocates after polymerization reaches the end of the template. (E) It shortens the length of telomeres and leads to disastrous results.

30. During the embryonic development, homeotic genes: (A) determine the dorsal-ventral polarity. (B) control the number of body segments. (C) encode morphogens that establish gradients. (D) are usually expressed by the mother during oogenesis. (E) are defined by mutations that convert one anatomical structure into another.

複選題31. Which of the following components are usually absent in the processed pseudogene that arises from integration of reverse-transcribed mRNAs? (A) Exon. (B) Intron. (C) Poly-A tail. (D) Promoter. (E) 3' untranslated region.

複選題32. Which of the following mutation types may lead to frameshift mutation? (A) Point mutation. (B) Insertion. (C) Deletion. (D) Substitution. (E) Missense mutation.

複選題34. Which of the following statements are correct regarding RNA splicing? (A) Release of group I introns is catalyzed by spliceosomes. (B) An intron is spliced out through two transesterification reactions. (C) The 5' splice site is recognized by the U1 snRNP. (D) Group II introns are the most commonly used for eukaryotic genes. (E) Group I introns release a linear intron.

複選題35. Which statements are correct regarding the expression of the lac operon? (A) Genes in the lac operon are expressed at high levels when both lactose and glucose are present at high levels. (B) The site bound by the lac repressor is called the lac operator. (C) The lac repressor is expressed regardless of whether or not lactose is present. (D) The lac operon is not transcribed when neither the activator nor the suppressor binds its site on DNA. (E) Catabolite activator protein (CAP) binds to the CAP site when glucose is absent.

複選題36. Which steps take place during the establishment and maintenance of lysogeny? (A) The N and cro genes are transcribed, but the cII and cIII genes are not transcribed. (B) The CII protein binds a site upstream from PRE. (C) The repressor protein stimulates transcription of the cI gene and binds OR and OL. (D) The Cro protein binds OR and stimulates transcription of the cro and cII genes. (E) The Q protein helps the RNA polymerase to transcribe through TR'.

複選題37. Which rRNAs are included in the eukaryotic ribosomes? (A) 5S rRNA. (B) 16S rRNA. (C) 18S rRNA. (D) 23S rRNA. (E) 28S rRNA.

複選題38. Which are correct regarding riboswitches that regulate translation initiation? (A) These riboswitches are typically found within the 3' untranslated region. (B) Each riboswitch is made up of an aptamer and an expression platform. (C) The aptamer undergoes structural changes in response to the changes in the expression platform. (D) The ribosome-binding site is typically found in the expression platform. (E) The ligand-binding site is typically found in the aptamer.

複選題39. Which of the following statements are correct regarding RNA silencing? (A) Small interfering RNAs (siRNAs) are derived from hairpin precursor RNAs. (B) MicroRNAs (miRNAs) are derived from double-stranded RNAs. (C) Both siRNAs and miRNAs are generated by the enzyme called Dicer. (D) The small RNA complement to the target mRNA is called the passenger RNA. (E) RNA-dependent RNA polymerase can enhance the efficiency of RNA silencing.