Q3 - Ordering a Proline Biosynthesis Pathway by Cross-Feeding

Theoretical A Real exam question - full text reproduced under IBO's CC BY-NC-SA 4.0 license

Scientists have isolated three different strains of bacteria ProA¯, ProB¯, and ProC¯ that require added proline for growth. One is cold-sensitive, one is heat-sensitive, and one has a gene deleted. Cross-feeding experiments were carried out by streaking the strains out on agar plates containing minimal medium supplemented with a very low level of proline. In cross-feeding experiments, metabolites leaking from one strain can feed a neighbouring strain. After growth at three temperatures, the results were shown in Figure Q.3.

Figure 1. Figure 1.

Using the information and data, determine which of the statements are true or which are false.

A. The intermediate that accumulates in the ProC¯ strain comes after the block in the ProA¯ strain.

B. The intermediate that accumulates in the ProB¯ strain comes after the block in the ProA¯ strain

C. There are at least three different genes that affect proline biosynthesis.

D. Under at least one condition, the proline that is produced is rapidly used for protein synthesis and is prevented from being synthesized in excess of needs.

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Question reproduced from IBO 2016, Theoretical Paper A, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)