broken ends (The above was the criteria that ta used to grade. Prof. Zhang suggested that 3 points are assigned to answer the causes of DSB, and 7 points are assigned to answer the RecBCD repair pathway in E. coli. Answer of nonhomologous end joining will be awarded to I point at most这题主要是test大家是不是熟练掌握了细菌里的 RecBCD修复机制) 3. What are the three principle classes of transposable elements? Who discovered the transposition? What do you leaned from the research career of the person who discovered transposition?(10 points) 1) The three principal classes of transposable elements DNA transposons, 2 Viral-like retrotransposons(LTR retrotransposons); 2 Poly-A retrotransposons(nonviral retrotransposons) 2 2)Barbara McClintock discovered transposable elements in maize in the late 1940s 3)This is an open question, so just write down your own opinions(e.g. about perseverance, strong interest, hard-working, etc. 4. Please describe how the transcription in bacteria is initiated elongated and terminated?(10 points) (1)Initiation(4): The initiation factor o recognizes and binds to promoter(1).In the case of e. coli. the most common g factor is g that contains two conserved sequences: -35 and-10 regions. Binding of the o factor facilitates rna polymerase to bind the promoter dNA, which forms a close complex, then the promoter is melted to form the open complex, and synthesis of RNA is then started. RNa polymerase usually has to synthesize several short RNAs before escaping from the promoter region to enter the elongation phase. Promoter escape requires the dissociation of the o factor from the core polymerase 2)Elongation(3): RNa polymerase synthesis RNA, unwinds DNA in front re-anneals it behind, dissociate the growing RNA chain. In addition, RNa polymerase carries out two proofreading functions as well. Rna polymerase catalyzes the removal of one incorrectly inserted ribonucleotide by reincorporation of PPi, called pyrophosphorolytic editing. RNa polymerase can also backtracks by one or more nucleotides and cleaves the rna product stimulated by Gre factors, called hydrolytic (3) Termination(3): Transcription in bacteria can be terminated by rho-independent or rho-dependent mechanism Rho-independent termination requires the terminators contain a short inverted repeat rich in G and C followed by a stretch of about eight A:T base pairs. After the terminator transcription, the mRNA can form a strong hairpin structure followed by a stretch of weak A: U base pairs with its DNA template and mRNA easily dissociates from the DNa template. Rho-dependent termination requires no intrinsic terminator RNA structure but requires rho factor that uses the energy derived from atP hydrolysis to stop transcriptionbroken ends. 2’ (The above was the criteria that TA used to grade. Prof. Zhang suggested that 3 points are assigned to answer the causes of DSB, and 7 points are assigned to answer the RecBCD repair pathway in E. coli. Answer of nonhomologous end joining will be awarded to 1 point at most.这题主要是 test 大家是不是熟练掌握了细菌里的 RecBCD 修复机制) 3. What are the three principle classes of transposable elements? Who discovered the transposition? What do you learned from the research career of the person who discovered transposition? (10 points) 1) The three principal classes of transposable elements: DNA transposons; 2’ Viral-like retrotransposons (LTR retrotransposons); 2’ Poly-A retrotransposons (nonviral retrotransposons) 2’ 2) Barbara McClintock discovered transposable elements in maize in the late 1940s. 2’ 3) This is an open question, so just write down your own opinions (e.g. about perseverance, strong interest, hard-working, etc.). 2’ 4. Please describe how the transcription in bacteria is initiated, elongated and terminated? (10 points) (1) Initiation (4’): The initiation factor σ recognizes and binds to promoter (1’). In the case of E. coli, the most common σ factor is σ 70 that contains two conserved sequences: -35 and -10 regions. Binding of the σ factor facilitates RNA polymerase to bind the promoter DNA, which forms a close complex, then the promoter is melted to form the open complex, and synthesis of RNA is then started. RNA polymerase usually has to synthesize several short RNAs before escaping from the promoter region to enter the elongation phase. Promoter escape requires the dissociation of the σ factor from the core polymerase. (2) Elongation (3’): RNA polymerase synthesis RNA, unwinds DNA in front, re-anneals it behind, dissociate the growing RNA chain. In addition, RNA polymerase carries out two proofreading functions as well. RNA polymerase catalyzes the removal of one incorrectly inserted ribonucleotide by reincorporation of PPi, called pyrophosphorolytic editing. RNA polymerase can also backtracks by one or more nucleotides and cleaves the RNA product stimulated by Gre factors, called hydrolytic editing. (3) Termination (3’): Transcription in bacteria can be terminated by Rho-independent or Rho-dependent mechanism. Rho-independent termination requires the terminators contain a short inverted repeat rich in G and C followed by a stretch of about eight A:T base pairs. After the terminator transcription, the mRNA can form a strong hairpin structure followed by a stretch of weak A:U base pairs with its DNA template, and mRNA easily dissociates from the DNA template. Rho-dependent termination requires no intrinsic terminator RNA structure but requires Rho factor that uses the energy derived from ATP hydrolysis to stop transcription