未知题型 由于日月地绕转，在地球上的月球直射点可达赤道南北28o...

单项选择题 课堂教学应该面向（ ），以（ ）为中心。

未知题型 二、FILL IN: (20 points, 1point for each) 1. Any piece of DNA which replicates as a single unit is called a ( ). 2. Almost all RNA start sites consist of a ( ) residue. G is more common at the transcription start site than A. 3. RNA Pol III synthesizes the precurssors of ( ) rRNA, tRNA and other ( ) and cytosolic RNAs. Like RNA Pol II, it is located in the ( ). 4. The tRNA ( ) adds the sequence 5’-CCA-3’ to the 3’-end to generate the mature 3’-end of the tRNA in tRNATyr processing of eukaryotes. 5. The replicase in prokaryotes is ( ), while in eukaryotes is ( ). 6. The major force involved in maintaining the secondary structure of protein is ( ) bond. 7. In NER，an endonuclease ( ) cleaves the DNA a precise number of bases on either side of the lesion. In E.coli, the gap is filled by ( ) and the final phosphodiester bond made by ( ). 8. Enzymes exist which regulate the level of supercoiling of DNA molecules, these termed ( ). 9. The ( ) factor is not required for transcription elongation and is released from the transcription complex after initiation. The remaining enzyme, which translocates along the DNA, is known as the ( ) enzyme. 10. The assembled ribosome has two tRNA-binding sites. These are called the A- and P-sites, for ( ) and ( ) sites. 11. Alternative splicing includes the following items: alternative selection of ( ), alternative selection of poly(A), retention of an ( ) and ( ) skipping.