在上期中，我们展示了一个学生的PS原文，和炜超老师的点评，本期我们来看看经过炜超老师修改的PS。

My dream of becoming an expert in biology can be traced back to my elementary school days. I managed small gardens fenced by lines of bushes, overflowing with flowers, willows, syringes, birds and bees. After my class, I used to run into the garden and watch the birds playing in the trees and bees singing in the flowers. As a young 11-year-old child, this world seemed so appealing and vivid. Oscar Wilde once said “Memory is the diary that we all carry about with us.” It is true and this diary determined my future development. To achieve my dream, I knew biology was the path I wanted to take at Wuhan University.

When I was in Wuhan University, I become more and more interested in biology. I knew it could bring me happiness and satisfaction. Sometimes, the knowledge I encountered was not described clearly. The library became my treasure-house to discovering the related materials to deal with problems. During the sophomore year in the class of Molecular biology, I was entirely enthused in “Transposition in recombination”. This kind of gene recombination is introduced simply in textbook; therefore I found out the GENE vii in library and sought some concerning related materials on the website of the Stanford University: highwire.org. After collected plenty of materials and information, I acquired many contents about it, such as its special structure frame, its own mechanism of recombination, which does not rely on any relationship between the sequences at the donor and recipient sites. One of its features that interests me is that they could move along with additional sequence; at that time, I thought it could provide new biotechnology to bring mutations in the genome. Later another realm-retrovirus, many Labs study now, proves my supposition correct. During the first two-year academic study, I was preparing for rigorous mental demands of doing research in the field of Biochem. & Molecular biology.

Chances were given to well-prepared people. In 2005, the junior year, I participated in the interview of recruiting research assistants, held by the State Key Molecular Virology Lab. With substantial command of academic knowledge, I won one of three offered positions against other 25 students from my grade. That was a good start of interweaving of my theory study and practice. I benefited a lot from this experience. I participated (joined) in the projects of “Identification of SARS-CoV Nonstructural Protein 14 and Characterization of its Activity” which are based on subgenomic mRNAs research primarily carried on our lab, aimed to identification and discovery of new activities of nonstructural proteins in coronavirus RNA synthesis and processing.

My first job, plasmid extraction, was a simple work but gave me a good introduction on Lab experience. From the view of economy, plasmid extracting in my lab is carried out by ….method. Before the work, I studied the Laboratory Manual, Molecular Cloning, and did experiment totally based on the steps it offered. However, the productivity of the plasmids cannot reach the normal level in my lab. After discussing with my instructor, I found out that there are some little changes in the step of resting on ice 30 minutes replaced by in the refrigerator for 20 minutes based on former experience.

My Lab life starts. To be best involved in this investigation, I made many preparations in many aspects such as dealing with genome organization of SARS-CoV and SARS-CoV special replication mechanisms of -1frameshift ORF reading, and code’s structural protein and functional protein. I refer to some important materials, like <Severe acute respiratory Syndrome Corona virus Group-specific Open Reading Frames Encode Nonessential Functions for Replication in Cell Cultures and Mice > published in 2005; < mechanisms and enzymes involved in SARS-CoV genome expression > in 2003; < identification and characterization of severe acute respiratory syndrome Coronavirus Replicase proteins>in 2004 from JGV, JV, JBC and etc. After accumulated enough academic knowledge about this field, I began to independently complete producing the antibodies against nsp3 in rabbits for detecting the mature protein product in Vero cell. But during the process of experiments, I encountered some problems. When I clone the nsp3 PCR fragment cleaved by Nco1 and Xho 1, the fragment was always larger than predicted mass 819bp. As the beginning, I thought the problem was caused by the unreasonable process. Therefore, from the PCR step, choosing of restriction endonucleases, to the taq ligase I did the whole experiment again and again. However, the problem was still not resolved. I, through discussing with the instructor, decided to check the origin of the sequence for PCR, and then I sent this segment of gene to the HuaDa Gene-sequencing Company in Beijing, finding that there is one transposon in the fragment.

Now, thanks to my exemplary lab performance and with the approval of my teacher, I am working in another research project “Expression and Purification of Recombinant Hepatitis B core antigen and development of a new sandwich ELISA” in which I directly took part in the new independent research of the project for the first time. In this project, I have finished my graduation thesis “Establishment and Evaluation of Double-antigen Sandwich ELISA detecting anti-HBc in human serum” and one paper “Development of a new double-antigen sandwich ELISA kit for antibody to hepatitis B core antigen in human serum” has been completed and submitted. Through the project, we set up a new way of using immuno-affinity chromatography to purify recombinant Hepatitis B core antigen protein. Because this protein will be used to set up the test method of ELISA, it must keep antigenicity. However, during the present process of rHBcAg purification, I found that elution buffer make targeted proteins denaturalize. After discussing with other researchers, I tried to test seven different elution buffers from PH 1.5, 2.5 to PH11.5 and added in magnesium salt and kalium salt to identify the influence of intense ion intensity. Finally, I found out the suitable elution buffer (0.1M TEA, pH 11.5). It seems like experiment is a course that you have to face new problems and defeat them. During experiment, I have been studying new things, learning the HRP-labeling HBcAg, mastering new technology ELISA, and acquiring immuno-affinity chromatography, all of which gives me a big present of experience and satisfactions of my mind.

The projects actually proved to me that the field of biology will fit my interests the best of all subjects. It appeals to my disciplined and inquisitive nature. Besides, my research in the Labs and my course work in classes have given me the analytical ability laboratory skills, and theoretical knowledge to excel in a rigorous doctoral program. And your esteemed university can help me to scale higher academic height in the field of biology. Your program is very appealing to me for free air research, good reputation and outstanding achievements, especially those innovative programs and courses offered at … Extensive work and model studies in several areas such as molecular biology and microbiology have been carried out. These things appeal to me deeply, for I intend to conduct research in these areas; I consider your program an ideal place for me to conduct in-depth and meaningful work.

　　从这个案例我们可以看出，PS的写作是一个需要集英文水平、专业知识、写作技巧、对西方教授思维方式的掌握、对PS结构的理解、以及丰富的PS写作经验于一体的高创造性过程。而不象有些人认为的，找个模板堆砌一些英文子句就行的简单劳动。

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