Cell Biology

Instructions

Each    question    should    be    answered    within    1    page    (single    or    1.5-spaced,    1margins,    12    point    font),    although    additional    pages    can    be    used    for    figures    and    references    if    necessaryQUESTIONS1. Cohesin forms a circular structure that tethers replicated DNA to hold sisterchromatids together. We discussed the cohesin complex in class, and how thevarious subunits assemble in an ATP-dependent manner. However, we didntdiscuss how the cohesin complex is loaded and locked onto DNA, especially during replication. Find two research articles published in the last 5 years that reveals mechanism(s) by which cohesin is loaded and/or locked onto chromatin, and briefly summarize their findings. Be sure to incorporate this knowledge into a modelof cohesin function.2. Some organisms, such as naked mole rats, either dont get cancer or have a low incidence of getting cancer despite their longevity (~30 years vs. 4 years for mice). Interestingly, their fibroblasts secrete a high molecular mass variant of hyaluronan, an extracellular matrix component, which accumulates in the surrounding tissues. Interestingly, this gives them an advantage for tunneling underground by giving them skin with high elasticity, but also has the added benefit of inhibiting cell division (see link to article below). Their cells display early contact inhibition (ECI), where they inhibit the growth of neighbouring cells when they come into close proximity. Describe the pathway by which HA inhibits cell division, as described in the article. Relate this to material that was covered in class and indicate how/when this blocks the cell cycle. Lastly, what did the authors do to induce tumour formation in naked mole rats?https://www.nature.com/nature/journal/v499/n7458/full/nature12234.html3. Dolly was the first mammal cloned by somatic cell nuclear transfer (SCNT), and she made headlines around the world. While she developed as expected into an adult sheep, she was euthanized at 6.5 years old after suffering from several age-related illnesses. The lifespan of her species is ~11-12 years old, and her telomeres were short compared to other sheep her age, which led to a debate as to how old Dolly really was. Subsequent studies have found no, or minimal health defects in other sheep cloned by SCNT arguing against this theory (e.g. see link to article below). Why is telomere length considered a determinant of age, and is it the only factor 2 that should be considered why or why not? Find one research article that describes a study where telomere length was linked to the age of an organism, and briefly summarize it.https://www.nature.com/articles/ncomms123595. The asymmetric localization of proteins during the first C. elegans division is crucial to give rise to the future body plan. Similarly, Drosophila neuroblasts divide asymmetrically to produce a cell that eventually differentiates into neurons, and another neuroblast. Ken Kemphues and his lab discovered the PARs partitioning defective genes, some of which are highly conserved and play a crucial role in regulating asymmetric division in C. elegans embryos and Drosophila neuroblasts, among other organisms and cell types. How do the PARs (and other proteins) create and maintain unique cortical domains (e.g. anterior vs. posterior or apical vs. basal)? How do these domains influence the mitotic spindle to ensure that they divide asymmetrically? To make it easier, describe how this works in one system (e.g. C. elegans or Drosophila), and be sure to include one or two references to support your answer.Ignore the parts that say relate the material the things covered in class

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