◼ What are the main challenges of translation and how do organisms overcome them? ◼ What is the organization of nucleotide sequence information in mRNA? ◼ What is the structure of tRNAs, and how do aminoacyl tRNA synthetases recognize and attach the correct amino acids to each tRNA? ◼ How does the ribosome orchestrate the translation process?

Although DNA replication, repair, homologous recombination occur with high fidelity to ensure the genome identity between generations, there are genetic processes that rearrange DNA sequences and thus lead to a more dynamic genome structure Two classes of genetic recombination for DNA rearrangement: • Conservative site-specific recombination (CSSR): recombination between two defined sequence elements • Transpositional recombination (Transposition): recombination between specific sequences and nonspecific DNA sites

◼ All DNA is recombinant DNA. ◼ Genetic exchange works constantly to blend and rearrange chromosomes, most obviously during meiosis, when homologous chromosomes pair prior to the first nuclear division. ◼ During this pairing, genetic exchange between the chromosomes occurs. This exchange, classically termed crossing over, is one of the results of homologous recombination

Q1. Prokaryotic cell E. coli consists of a single closed-circular DNA molecule of 4.6 x 106 bp long. This DNA molecule would be 1.6 mm if the double helix is relaxed. Please describe what strategies does E. coli use to pack such a long molecules into its nucleoid less than a micrometer (mm) in diameter. (20 points)

1. Please define the term “mutation”, and list the major types of DNA mutations and their corresponding phenotypic effects. (20 points) 2. Please define the term “DNA lesion”. Please list the three types of DNA lesions and the chemical or physical mutagens cause these lesions. (20 points)

Q1. Prokaryotic cell E. coli consists of a single closed-circular DNA molecule of 4.6 x 106 bp long. This DNA molecule would be 1.6 mm if the double helix is relaxed. Please describe what strategies does E. coli use to pack such a long molecules into its nucleoid less than a micrometer (mm) in diameter. (20 points)

（1）不离开自己的座位。（2）收起书和笔记，不可放 在桌面上。（3）只能看和写自己的试卷（4）老师宣布 停的时候，所有学生必须放下自己的笔，眼睛 向前看。 （5）老师宣布收试卷时，试卷必须快速由每排的最左 边传向右边，每排最右边的同学负责把试卷交给当堂助 教

（1）不离开自己的座位。（2）合上书和笔记。（3） 个人只能看和写自己的试卷（4）老师宣布停的时候， 所有学生必须放下自己的笔，眼睛 向前看。（5）老师 宣布收试卷时，试卷必须快速由每排的最左边传向右边， 每排最右边的同学负责把试卷交给当堂助教

（1）桌上只有笔和答题纸。（2）不离开自己的座位。 （3）不偷看，不讲话 (有问题举手）（4）老师宣布停 的时候，必须放下自己的笔。（5）老师宣布收试卷时， 试卷必须快速由每排的最左边传向右边，每排最右边 的同学负责把试卷交给当堂助教

2.不许离开自己的座位，不许看他人试卷，不许讲话 (有问题举手） 3.老师宣布收试卷时，试卷必须快速由每排的最左边传向右边，每排最右边的同学负责把试 卷交给当堂助教。迟交者不收！