Cell Communication

Introduction:
Yeast cells have two "sexes," called a-type and alpha-type. They locate each other via specific secreted factors. The exchange of factors causes them to mate. When these two cultures mix, the haploid cells (meaning they only have one complete set of chromosomes) become gamete cells (a mature sexual reproductive cell). The yeast cells halt asexual reproduction and grow into pear-shaped gametes called schmoos. When a-type and alpha-type come into contact with each other, they fuse, and the haploid nuclei form a diploid nucleus.

Purpose: The purpose of the lab was to analyze the cell signaling that occurs between the alpha-type and a- type yeast cells. The mating interaction of the two yeast types mixed together was the focus of the experiment. Our results for the mixed culture should support the idea of yeast cells mating with the use of special factors that attach to the opposite mating type. The characteristics of each yeast cell type were also individually analyzed.

Methods: 

1.We labeled 3 agar plates and 3 culture tubes as alpha-type, a-type, or mixed.

2. We added about 2 mL of sterile water to each tube and transferred a small amount of each yeast type into its designated tube.

To do this we used a toothpick to gather yeast cells and mixed the yest cells with the sterile solution by swishing the toothpick in the solution. For the mixed culture, we gathered a-type cells with a toothpick and placed it into the solution. Then with a different toothpick we gathered alpha-type cells and placed it in the same solution. Drops of yeast suspension were placed on their designated plates. We used different cotton swabs like in the picture below to spread the suspension on the agar plates.

 

 We then looked at the yeast under the microscope at different intervals of time to see what occurred in the life cycle. We captured images at 0 minutes,30 minutes, and 24 hours later. Unfortunately, the 0 and 30 minute images are unable to upload, but below are images of the alpha-type, a-type, mixed-type, and experiment yeast suspensions on the agar plates after 24 hours.

Mixture of alpha and a type saw the most growth on the agar plate. Best cell communication

alpha type yeast saw some growth too, but still not as dense as the mixed plate. Mating factors of the different yeast type can signal the opposite sex type, which impedes cell communication.

a type yeast cells grew a bit

we placed alpha and a type yeast on opposite ends of the plate (separated). Growth occured in the sides of each individual type but failed to develop towards the middle of the plate since the mating factors never or barely came in contact.



Data/graph

 

Discussion 

A large part of analyzing this lab is noticing the differences in the yeast over a period of time. In order from least amount of change to most amount  of change overnight it goes; the mixed separate dish, a-type, mixed, and then alpha-type. The reasons that the separate mixed was the least had to do with the fact that we started the yeast on opposite sides of each other. This makes it difficult for the yeast cells to sense the actual amount of cells in the dish, and therefore they do not shmoo as much as they should. Even when they do, it is a far distance across the dish for these little cells to get to. This slows down the overall process even more. The reasoning for the mixed being one of the highest producing ones is because it was mixed. This gives more opportunity for diversity within the cells and makes them able to produce faster. The reasons, I believe, that alpha was the largest change, was just due to its genetic make-up. It was obviously more adapted to move and produce quickly. This experiment proves how cells communicate with one another. After they got to a certain density, they stopped producing. We were also able to see how they changed their cytoskeleton to reach one another. This experiment truly shows how cells signal one another. 

Conclusion:
This lab proves that yeast cells communicate through pheromones, also known as chemical signals transmitted between organisms. Because a-type and alpha-type cultures changed into their gamete form, they detected a signal from the opposite type. Also based on the fact that alpha-type yeast changed the most, we can conclude that this type releases the most mating factor.