Biochemistry 1731c

生物化學小考(四)

範圍 ch12~ch16

單選題(每題 2 分, 總分 20 分) 1. The compound that consists of ribose linked by an N-glycosidic bond to N-9 of adenine is: (A) a deoxyribonucleoside. (B) a purine nucleotide. (C) a pyrimidine nucleotide. (D) adenosine monophosphate. (E) adenosine. 2. The difference between a ribonucleotide and a deoxyribonucleotide is: (A) a deoxyribonucleotide has an —H instead of an —OH at C-2. (B) a deoxyribonucleotide has α configuration; ribonucleotide has the β configuration at C-1. (C) a ribonucleotide has an extra —OH at C-4. (D) a ribonucleotide has more structural flexibility than deoxyribonucleotide. (E) a ribonucleotide is a pyranose, deoxyribonucleotide is a furanose. 3. The alkaline hydrolysis of RNA does not produce: (A) 2’- AMP. (B) 2’,3’-cGMP. (C) 2’-CMP. (D) 3’,5’-cAMP. (E) 3’-UMP. 4. The DNA oligonucleotide abbreviated pATCGAC: (A) has 7 phosphate groups. (B) has a hydroxyl at its 3’ end. (C) has a phosphate on its 3’ end. (D) has an A at its 3’ end. (E) violates Chargaff’s rules. 5. For the oligoribonucleotide pACGUAC: (A) the nucleotide at the 3’ end has a phosphate at its 3’ hydroxyl. (B) the nucleotide at the 3’ end is a purine. (C) the nucleotide at the 5’ end has a 5’ hydroxyl. (D) the nucleotide at the 5’ end has a phosphate on its 5’ hydroxyl. (E) the nucleotide at the 5’ end is a pyrimidine. 6. When a DNA molecule is described as replicating bidirectionally, that means that it has two: (A) chains. (B) independently replicating segment. (C) origins. (D) replication forks. (E) termination points. 7. The 5’→3’ exonuclease activity of E. coli DNA polymerase I is involved in: (A) formation of a nick at the DNA replication origin. (B) formation of Okazaki fragments. (C) proofreading of the replication process. (D) removal of RNA primers by nick translation. (E) sealing of nicks by ligase action. 8. The ABC excinuclease is essential in: (A) base-excision repair. (B) methyl-directed repair. (C) mismatch repair. (D) nucleotide-

excision repair. (E) SOS repair. 9. After binding by E. coli RNA polymerase, the correct order of events for transcription initiation is: (A) closed complex formation, open complex formation, promoter clearance, start of RNA synthesis. (B) closed complex formation, open complex formation, start of RNA synthesis, promoter clearance. (C) open complex formation, closed complex formation, start of RNA synthesis, promoter clearance. (D) start of RNA synthesis, closed complex formation, open complex formation, promoter clearance. (E) start of RNA synthesis, open complex formation, closed complex formation, promoter clearance. 10. The 5’-terminal cap structure of eukaryotic mRNAs is a(n): (A) 7-methylcytosine ed to the mRNA via a 2’,3’-cyclic linkage. (B) 7-methylguanosine ed to the mRNA via a 5’→3’ diphosphate linkage. (C) 7-methylguanosine ed to the mRNA via a 5’ →5’ triphosphate linkage. (D) N6-methyladenosine ed to the mRNA via a 5’ →5’ phosphodiester bond. (E) O6-methylguanosine ed to the mRNA via a 5’→5’ triphosphate linkage.