Examination Candidate Number: Desk Number: UNIVERSITY OF YORK BA, BSc, and MSc Degree Examinations 2017-8 Department : BIOLOGY Title of Exam: Molecular microbiology Time Allowed: 1 hour 30 minutes Marking Scheme: Total marks available for this paper: 80 Sec on A: Short answer ques ons (30 marks) Sec on B: Problem ques ons (20 marks) Sec on C: Long answer ques on (marked out of 100, weighted 30 marks) The marks available for each ques on are indicated on the paper Instructions: Sec ons A and B answer all ques ons in the spaces provided on the examina on paper Sec on C answer either ques on A, B or C, write your answer on the separate paper provided and a ach it to the back of the ques on paper using the treasury tag provided Materials supplied: CALCULATOR For marker use only: For office use only: 1 2 3 4 5 6 7 Module total as % DO NOT WRITE ON THIS BOOKLET BEFORE THE EXAM BEGINS DO NOT TURN OVER THIS PAGE UNTIL INSTRUCTED TO DO SO BY AN INVIGILATOR page 1 of 8
SECTION A: Short answer questions Answer all questions in the spaces provided Mark total for this section: 30 1. Diauxic growth occurs when Escherichia coli is grown on a mixture of glucose and lactose as a carbon source. A schematic of diauxic growth of a bacterial culture is shown in the graph below with a solid line. a) Add a dashed line to the graph above for glucose concentration in the culture liquid, and identify in the graph, or describe in words, when the camp concentration is high. (1 mark) b) Briefly outline the key molecular events that lead to an increase in the bacterial camp level. page 2 of 8
c) How does camp help coordinate expression of different genes in E coli? (1 mark) 2. srna, a riboswitch or RNA binding protein can all affect translation. a) Which step in gene expression can be controlled by all three of these mechanisms? (1 mark) b) Two different proteins are reduced in expression when a small organic molecule is added to a culture.you find that expression of one gene is controlled by an srna and the other by a riboswitch, both in response to the compound. Identify two differences between these mechanisms regarding how the compound leads to changes in gene expression. (4 marks) (i) (ii) The space above this line should be sufficient for your answer. page 3 of 8
3. a) Compare and contrast the assembly of proteins via the Sec and Tat pathways. (5 marks) b) Outline the structure and function of the Type 3 Secretion System. (5 marks) page 4 of 8
4. a) Which are the enzymatic activities of the Rho terminator protein? (2 marks) b) How do these activities mediate transcription termination? c) If multiple amino acid substitutions are introduced in the N-terminal domain, what function of Rho would be affected? (1 mark) 5. a) Describe the role of the AraC protein in the presence of arabinose. b) If the AraC N-terminal arm is deleted, how does the protein function in the: (i) presence of arabinose? (0.5 mark) (ii) absence of arabinose? (0.5 mark) page 5 of 8
SECTION B: Problem questions Answer all questions in the spaces provided Mark total for this section: 20 6. You are researching a particular bacterial species, and you suspect there are two different genes both encoding superoxide dismutase (SOD) enzymes. Outline approaches to: a) Determine whether the two SOD enzymes are closely related to one another. (2 marks) b) Predict whether the enzymes are located in different parts of the bacterial cell. (2 marks) c) Predict whether the two enzymes are expressed in response to different environmental cues. page 6 of 8
d) Determine experimentally whether the two enzymes are expressed in response to different environmental cues 7. You have sequenced the genome of a bacterium isolated from the lake at the University of York and have named it Jorvikia coli. The assembled chromosome is 5.2 Mb and you have also assembled a 500 kb plasmid. a) Estimate how many genes are likely present in the chromosome and explain how you reached this number. b) What experiments could you use to determine if genes present in the plasmid are essential for the bacterium to grow? c) The Jorvikia coli genome contains a prophage sequence in its genome. How would you determine whether this prophage was still active or was cryptic? (4 marks) page 7 of 8
SECTION C: Long answer question Answer one question on the separate paper provided Remember to write your candidate number at the top of the page and indicate whether you have answered question A, B or C Mark total for this section: 30 EITHER A) Discuss biological nitrogen fixation, focusing on why, and how, the process is tightly regulated. OR B) Discuss why the ability of regulatory proteins to change conformation in response to small-molecule ligands is an effective strategy to regulate gene expression in bacteria. OR C) Describe, with examples, how growth experiments can inform us about gene function in microbiology. page 8 of 8