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We conducted several experiments with Saccharomyces cerevisiae, in order to study the life cycle of yeast, the principles of complementation, and tetrad analysis. The life cycle of yeast can be easily studied at various stages because it reproduces through budding and exhibits predictable morphological changes in this process. Genetic complementation is the reappearance of the wild-type phenotype in offspring when there are two different homozygous recessive mutations present in the parent organisms. Complementation can be easily observed in yeast using the ADE mutations. If the ADE mutations, which inhibit adenine biosynthesis, are on separate genes, then complementation will occur. Complementation in yeast would result in the ability to produce adenine, even though neither of the haploid strains are capable of doing so. Tetrad analysis involves examining the completion of the entire yeast life cycle.

The author’s central argument is that there are occasions where killing someone is better than letting someone die. She uses Nesbitt’s ‘Smith and Jones’ scenario to prove that Nesbitt’s ‘difference thesis’ (states that killing someone is morally worse than letting someone die) is false. Kuhse goes on to say that killing someone is not necessarily an evil thing nor harming the patient when it comes to the field of medicine. Life isn’t always good and can be filled with suffering. It is when the patient is suffering that killing the patient is better than letting the patient die. If the doctor were to leave the patient to die on his own, that would not be beneficial to the patient and would be seen as incapacitated. We would not want those kinds of doctors nor people around us because they act like rocks or trees and do not feel compassion. Kuhse then provides his own examples of when killing is better than letting die.

After three days of incubation, the growth of yeast on each plate was unique. On the YED plate, all colonies grew very well, but some colonies were red while others were white (Figure 4). The MV+Adenine plate had all colonies grow well to a slightly lesser degree than the YED plate. The colonies on this plate were all white cells (Figure 5). The MV plate was the most drastic difference. While some colonies grew to the same degree as on the MV+Ade plate, there were colonies which were extremely weak, or completely non-existent. The colonies that were healthy were white, while the remains of sickly colonies were red (Figures 6 and 7).

Fruit flies (Drosophila melanogaster) go through a 4-stage life cycle. A life cycle that is 11-14 days long providing an efficient option for observations in a laboratory setting (Potter 2000-2016).  This cycle can be altered simply by exposing the larvae to different hormones. We were eager to see the effect varying concentrations of Juvenile Hormone, a hormone essential to fruit fly development, inhibitor had on the life cycle of a fruit fly in a lab setting (Yamamoto R1, Bai H, Dolezal AG, Amdam G, Tatar M. 2013). Because of the fact that the juvenile hormone is essential to fruit fly development we hypothesize that the overall development will be stunted and predict to see a larger percentage of larvae in trials that contain a higher concentration of inhibitor and a lower percentage of pupae in trials that contain a higher concentration of inhibitor. We mixed 10ml of water (Control) or various concentrations (0.01, 0.1, and 1) Juvenile hormone (JH) Inhibitor with 2 grams of dehydrated fly media. We then added 2 male and 2 female flies to each tube. For a week we let the flies mate in the media. In the second week we removed all the adults from each trial and placed the tubes back into the incubator. After the third week we scored the vials for: number of larva, number of pupa, number of males and female adults, average length of adults. As you can see in Figure 1 there is an upwards trend seen in the percentage of larvae as the concentrations increase, as supported by the fact that 14% of flies in the 0.01 concentration were larvae and in the vial a concentration of 1 approximately 38.4% of the full population is larvae. Also in Figure 2 a downward trend is seen in the percentages of pupae, as supported by the fact that 63.4% of the population in 0.01 concentration were in the pupae stage, while the population with a concentration of 1 only had 35.1% of the population in the pupae stage.

Both factors, osmolarity and volume, of blood have lasting effects on the body and the functions that occur throughout. Both factors change independent from each other, but work together to maintain an overall homeostasis within the body. For example if an individual were to work out and drank only water then the overall osmolarity of the blood would decrease due to the increase of water. However the volume will not change because the water lost in sweat would be replaced by the water consumed. The change in the osmolarity would lead to a reduction of vasopressin release and an increase in renin production. The renin production increase would promote the reabsorption of sodium, bringing the osmolarity back to an equilibrium state. This is a prime example of independent pathways that work together within the body in order to maintain homeostasis. 

Throughout the process of this lab many mechanisms of evolution were observable, most prominently the mechanism of natural selection. In order for evolution by natural selection to occur three requirements must be met. The first is that individuals in the population must vary in trait that is being considered. Also the trait be considered must also be heritable, meaning it must be able to be passed down from generation to generation through germline cells. Lastly there must a selection differential, which simply means that the trait being considered must either increase or decrease the likelihood of the organism to survive and reproduce. This idea of evolution through natural selection was discussed throughout the SimUText Lab and was displayed during the Flat Periwinkle snail activity. In the activity the trait of Periwinkle shell thickness was shown to be variable, heritable and provided a selection differential, in the case of this trait a thicker shell resulted in a greater likelihood to survive and reproduce in an environment that contained predation by crabs. This trend of thicker shells leading to a higher likelihood of survival and reproduction in Flat Periwinkle populations was the driving force behind the constructed hypothesis for the effects of crab predation on the Dogwinkle snail population. The Dogwinkle snail species is the species under observation in the experiment, the Dogwinkle species exists in two distinct factions, an Eastern and a Western. In the Eastern population there is a predation pressure due to the presence of Rock Crabs and the average shell thickness of the Eastern population is thicker than the Western population in which there is no Rock Crabs present. With all of this information under consideration the hypothesis reads as follows, if there is predation by crabs present and the trait of shell thickness is being observed, then evolution by natural selection will occur and a shift to a larger average shell thickness in the experimental tanks containing the Dogwinkle snails can be expected.

Dr. Chao’s current research involved how the mitochondria gets its shape and factors that influence mitochondrial organization. F1F0 ATP synthase dimers play a pivotal role in the formation of creases and folds in the mitochondria needed for increasing surface area. Dr. Chao showed this by increasing the amount of ATP synthase dimers, which in turn increased the number of creases and organization in the mitochondria observed. Dr. Chao also wanted to understand how dynamic membranes are regulated. This dynamic membrane and formation of cristae is regulated by a number of proteins included Mfn1/2 and OPA1, both of which are in the dynamin family of GTPases. Dr. Chao is currently looking to into the relationship between these proteins and membrane conformation.

Also importantly, they discovered the pre-fusion state envelope protein to be dimeric, while the post-fusion state envelope protein was trimeric. Based on these findings, Dr. Chao and Harrison conducted where they discovered yield of fused membranes increased if they increased the size of the contact patch, and yield decreased as the pH of buffer increased. They also were able to show that the trimerization of envelope proteins is a kinetic bottleneck, limited by the availability of monomers required for fusion. This is important because of its possible application in drug development. The kinetic bottleneck that Chao and Harrison propose means that full saturation would be needed in order to block entry, as opposed to drugs targeting SNAP/SNARE vesicle fusion, which fires and fuses rapidly in the presence of calcium.

Flavivirus is a genus of viruses that includes west Nile virus and cause severe disease such as yellow fever. Flavivirus genomic RNA replication occurs on the rough endoplasmic reticulum, in membranous compartments, and the focus of Dr. Chao and his advisor Dr. Stephen Harrison’s research at Harvard was the fusion of the viral and cellular membranes. Cellular entry by the virus requires this membrane fusion and in order to do so, viral fusion proteins undergo dramatic conformational rearrangements. These proteins, which exist on the surface of the viral envelope, must undergo conformational changes to create a thermodynamically favorable chemical reaction and overcome the energetic barriers to merge the two membranes and create hemisfusion (lost him a bit in the biochemistry on this part).  They discovered that the envelope protein comprised of three main domains, one largely hydrophobic involved in the fusion loop. In its pre-fusion state, the hydrophobic domain is tucked in the protein, however the hydrophobic domain extends into cell membrane then collapses to bring membrane together and create hemifusion and full pore opening.

The research seminar I attended was given by Dr. Luke Chao who is the head of a laboratory at the Department of Molecular Biology at Massachusetts General Hospital and the Department of Genetics at Harvard Medical School.  Dr. Chao received his B.S/M.S in Biochemistry from Brandeis University and received his Ph.D. in Molecular and Cell Biology from UC-Berkeley where he worked with John Kuriyan doing structural studies of calcium/calmodulin-dependent protein kinase II. The majority of Dr. Chao’s seminar discussed his work as a postdoctoral fellow in the laboratory of Stephen Harrison at Harvard investigating the mechanism of flavivirus membrane fusion, however, he also discussed briefly research he is currently conducting regarding the assembly and maintenance of cellular ultrastructures such as organelles.