Most of the eukaryotic genes are mosaic (嵌合体), consisting of intervening sequences separating the coding sequence ◼ Exons (外显子): the coding sequences ◼ Introns (内含子) : the intervening sequences ◼ RNA splicing: the process by which introns are removed from the pre￾mRNA. ◼ Alternative splicing (可变剪接): some pre-mRNAs can be spliced in more than one way , generating alternative mRNAs. 60% of the human genes are spliced in this manner

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

Quiz: Section K, L, M and N, 40 min, English answer only 1. Please list the important cis-acting elements and transacting enzymes/factors in prokaryotic transcription including initiation, elongation and termination, and briefly describe their corresponding roles (35 point)

1. What is “DNA cloning”? how could you make a genomic library cloning? (30 points) 2. What is “subcloning”? What are the purposes of subcloning. (15 points)

（1）开卷考试，个人独立完成 （2）不须偷看别人的答案 （3）老师宣布收试卷时，试卷必须快速由每排的最左

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)

Q1: Please name the following amino acids (three letter name, for example: Ala for alanine). Q2: Which of them are hydrophobic AA, and which are hydrophilic?

1. What are the gene expression stages that can be regulated? (10 points) Regulated stages in gene expression: (1) transcription initiation (the most important stage): RNAP binding of the promoter, transition from the closed complex to the open complex; promoter escape 4’ (2) stages after initiation (elongation and termination) 2’ (3) RNA processing (alternative splicing) in eukaryotes 2’ (4) translation 2’

1. Please describe the main features of the DNA structure. (10 points) Key features: (1) Double helical structure (4’) (2) Two strands are held together in an antiparallel orientation (3’) by base paring (1’)

Describing the following terms (4 points each) 1. Cre recombinase 2. CSSR recombination 3. Mating-type switching 4. Mismatch repair 5. Polymerase switching 6. 30-nm fiber 7. Core histones