Thursday, December 19, 2013

Yeast Lab 12/19

Purpose: The purpose of this lab was to demonstrate cell communication through different stages of the mating of yeast.
INTRODUCTION: Cells communicate through the release of chemical signals which illicit varying responses in the unicellular colonies. In this lab there are 2 types of yeast (a) and (alpha) they each secrete a mating (a) and (alpha) factor respectively. When the (a) type yeast cell receives the (alpha) factor and the (alpha) type yeast cell receives the (a) factor a change in the cytoskeleton of each yeast cell type undergoes a change. Each cell cytoskeleton elongates because of the opposite cell factor binding to a receptor on its cell membrane that caused a specific signal transduction pathway. The cytoskeleton elongating forms a shmoo, each shmoo veers towards one another and finally meet to form xxa zygote.
Cells communicate in order to relay information and thus illicit a cellular response. One way cells communicate is through g-protein coupled receptors. A signal stimulates the receptor to undergo a transduction pathway. During this transduction period, the signal molecule activates the receptor to displace GDP to GTP. This causes the g protein to activate, thus relaying the information it got from the receptor to a neighboring inactive enzyme. The active protein activates the enzyme, thus evoking a cellular response.
Methods:  We obtained alpha, a, and alpha/a mix yeast with broth in three different test tubes.
We made 3 different wet mounts that contained the alpha, a, and alpha/a cultures on each slide. To avoid contamination, we used three different pipettes when creating the wet mounts.
We placed these wet mounts under a light microscope. The zoom was calibrated, as it was difficult to focus on the mass of yeast cells. First we looked at the cultures at a X10 magnification then under a X40 magnification.
Then we looked for fields in which the yeast cells were possible to count. We chose 3 fields per wet mount. We took readings at intervals of time 0, 30 minutes, 24 hours, and a final reading at 48 hours. We recorded the amount of haploid, shmoo, zygote, asci, and budding cells there were per field.

Discussion: We isolated the two different groups into a isolated and alpha isolated. The two isolated cells did not show much  communication. In the 24 hour period, there was a decrease of alpha and an increase of A cells, but at the 48 hour mark there was an increase of A cells and a decrease of alpha cells. It seems as though both cells had
opposite living conditions under which they survive the best. Also, the budding of both cells might have undergone some fluxes due to various concentrations in different parts of the wet mount we saw. For example, the presence of air bubbles in the wet mount. The air bubbles pushed away the cells, making them compact and harder to count.
The mixed group showed many stages of cellular communication. We saw haploids, shmoo, zygotes, spores, and ascus. This, unlike the isolated colonies, showed a much higher rate and greater sophistication of cellular  communication. The formation of all of these was due to the sexual reproduction between alpha type and a type yeast cells.
The most particular formation was the pear-shaped shmoo cell. It gets its pear shaped from its ability to recieve a ligand (signal) through a g-protein coupled receptor. (to see how a g-protein works, see the introduction). The formation of shmoos would be an example of local signaling as the cell changes shape from within. Because the yeast cells don’t have the motor skills to move, it grows to a potential mate. The g protein coupled receptor sends that signal and tells the cell’s nucleus to grow towards where the signaling molecule concentration is the highest. Thusly, the cell will have a bigger chance to mate. This explains the pear shape of the shmoo as it grows towards a potential mate.

As you can see here is the Alpha yeast. This is the isolated apha culture that was allowed to reproduce asexually. You can see the rise and the fall of both the haploid and the budding haploid population
Below you have the Alpha Yeasts and A yeasts as isolated cultures. You can see the rise and fall of both Haploids and budding haploids over the 4 periods of time.

Based on our findings, we concluded that yeast cells communicate via direct contact as well as pheromones. Since the yeast cell does not have the ability to move on its own, the easiest way it can mate is by fusing with a close, neighboring cell. Pheromones come into play when the cells are more spread out. Signaling molecules (ligands) are ejected from the cell, thus motivating the alpha/a cells to grow towards where the signals are of greatest concentration. This produces shmoos. Once in close proximity, mating and sporulation occurs. Proximity is an important factor as to where shmoos will appear first in a petri dish with both alpha and a type yeast. Since it will be most efficient to send a ligand over a shorter distance, shmoos will appear first in the area of least distance between alpha and a type yeast. In a hypothetical situation, if we are given a petri dish with 4 distinct regions marked in the petri dish and 3 of the circles contain alpha type yeast and one circle contains a type yeast, presence of schmoos will first be detected in the alpha circle closest to the a type circle.

Conclusion: We concluded that the most cellular communication happened when the a culture was mixed with the alpha culture. The zygotes, shmoos, haploid cells, and asci proved that communication between alpha and A yeast cells needs more signals to carry out more complex responses. On the other hand, we have the separated a and alpha cells which, on their own, did communicate but only formed haploids and budding haploids. This asexual reproduction allowed for the yeast to multiply though not as fast like the mixed cells.

References: Lab


  1. References need to be a little more detailed. Nice job overall!

  2. A cuvette is a piece of laboratory equipment that is intended to hold samples for spectroscopic analysis.Cuvette

  3. I have been through the whole content of this blog which is very informative and knowledgeable stuff, I would like to visit again.
    Link -