Yeasts are single-cell microbes that usually reproduce asexually by a process called budding. Budding occurs when part of the cell is pinched off and develops into an identical cell.

Question

A) Identify a signaling molecule from the model presented. Explain how receptors play a role in cell differentiation.

B) Identify the dependent variable and two controls the experimenters used when conducting this experiment.

C) Evaluate if the number of Variant 1-Type cells with mating projections was significantly different from those of the Wild Type. Use chi-square analysis.

D) Scientists propose that a mutation has occurred that either changed the mating pheromone or receptor site on the Variant 1-Type yeast cells. Predict where the mutation occurred. Justify your prediction with evidence from the experiment and scientific reasoning, based on your knowledge of cell-signaling pathways.

Answer 1

A) One signaling molecule from the model presented could be the mating pheromone. Mating pheromones are released by yeast cells to signal their readiness to mate and attract mating partners. Receptors play a crucial role in cell differentiation by binding to specific signaling molecules (such as pheromones) and initiating intracellular signaling cascades that lead to changes in gene expression and cell behavior. In the case of yeast mating, receptors on the cell surface bind to mating pheromones, triggering a signaling pathway that ultimately results in cell fusion and mating.

B) The dependent variable in the experiment could be the number of yeast cells exhibiting mating projections (indicating readiness to mate). Two controls the experimenters could use are:

1. A negative control where yeast cells are grown in the absence of mating pheromones to assess background levels of mating projections.
2. A positive control where yeast cells of the Wild Type strain (known to respond to mating pheromones) are exposed to mating pheromones to ensure that the experimental conditions are conducive to mating projection formation.

C) To evaluate if the number of Variant 1-Type cells with mating projections was significantly different from those of the Wild Type, chi-square analysis could be performed. Chi-square analysis compares observed frequencies with expected frequencies to determine if there is a significant association between variables. The null hypothesis would be that there is no significant difference in the proportions of Variant 1-Type and Wild Type cells with mating projections. The chi-square test would provide a p-value indicating the probability of obtaining the observed results by chance. If the p-value is below a predetermined significance level (e.g., p < 0.05), the null hypothesis is rejected, suggesting that there is a significant difference between the groups.

D) Based on the proposal that a mutation has occurred that either changed the mating pheromone or receptor site on the Variant 1-Type yeast cells, it is likely that the mutation occurred in the receptor site on the Variant 1-Type yeast cells. This inference is supported by the observation that the Variant 1-Type yeast cells did not respond to mating pheromones in the same way as the Wild Type cells. If the mutation had occurred in the mating pheromone itself, the Variant 1-Type cells would still have been able to respond to mating pheromones produced by other cells in the population. However, the fact that they did not respond suggests that the mutation likely affected the receptor site on the Variant 1-Type cells, rendering them unable to recognize or bind to the mating pheromones. Therefore, it is reasonable to predict that the mutation occurred in the receptor site of the Variant 1-Type yeast cells.