Read the research paper by Santin et al., ‘In vitro activity of the essential oil of Cymbopogon citratus and its major component (citral) on Leishmania amazonensis’ (published in 2009 in the journal Parasitology Research, volume 105 (November), pages 1489–96). A PDF version of this paper is available from the ‘Assessment’ section of the module website, as is a web-page version of the same content.
You are advised to spend about 40 minutes reading the paper and making preliminary notes before answering the questions below. The paper contains many technical details, especially in the ‘Materials and methods’ section, that we do not expect you to understand. However, you should be able to understand the main points and how the ideas are developed through the article.
The following questions then test your understanding of key features of the style, structure and content of the article. Understanding the style and structure, and the use of simple diagrams, will help you in preparing your report for TMA 04, which contributes 25% of the marks towards your overall examination score (OES). Write no more than 1000 words and state your word count at the end of question 5. The abstract and full formatted reference do not count towards the word limit, neither do words within figures/diagrams. However, words within tables (including the title and caption and the column headings) are counted towards the word count as are in-text citations. You can obtain your word count using the Word Count tool in Microsoft Word, or equivalent.
- i. In one sentence, state what the authors set out to determine. (2 marks)
- ii. In the introduction to the paper, the authors state two main limitations to existing drugs. What are these limitations? (4 marks)
- iii. Summarise each of their three main findings and, for each one, briefly explain why the authors consider these findings to be important. (12 marks)
- i. Describe the data presented in Figure 1 of the paper and explain its relevance for developing drugs against Leishmania. (6 marks)
- ii. How do the authors account for the differences in the effectiveness of the essential oil (‘EO’) versus citral on parasite viability? (2 marks)
- c. The authors suggest several cellular targets and mechanisms by which the essential oil and citral damage and kill Leishmania parasites. List these cellular targets and summarise the evidence the authors present to support each mechanism of action. (16 marks)
- d. Give a brief evolutionary explanation for why plants such as Cymbopogon citratus contain compounds with anti-protozoan activity. (2 marks)
- i. Draw the life cycle of Leishmania amazonensis, with numbers for each step, and then use short sentences to describe the most important stages. This diagram should be your own work; you will not gain any marks for a diagram that is simply copied and pasted from the Internet, etc. Indeed, a direct copy-paste would be treated as plagiarism. We do not expect your diagram to be a piece of high-quality art; a simple block diagram, or something that is hand-drawn and then scanned, is fine. (Hint: one way to adapt a figure is to combine several pieces of information into a single new depiction). If you adapt an existing figure, then you must cite where the original image(s) came from, and include a screenshot of the original(s) at the end of your answer. (8 marks) In addition, search the Internet for a peer-reviewed article or review that provides additional details of how Leishmania parasites manage to remain in the sandfly midgut and then find their way to the mouthparts. Write a few short notes about this and paste the abstract of the paper into your answer, including the title, authors and journal name/volume/pages. (4 marks).
- ii. Describe the various ways in which Leishmania amazonensis is adapted to life inside a human host. (4 marks)
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