Monthly Archives: January 2016

Cell Cycle Movie

Our Cell Cycle Movie
This week, we created our stop motion movie of the cell cycle. In particular, this gave us a chance to trace a cell’s DNA through the cycle. First, in the synthesis stage, the DNA is duplicated, creating two new identical strands where before there was one. However, ideally these news strands will be exact copies of the original, and thus carry no new information. Before Mitosis, the DNA condenses into chromosomes by winding around specialized proteins, histones. This allows DNA to split into two identical copies of the same information, called sister chromatids, which ensures that each daughter cell will have the same genetic information. These sister chromatids are attached by a groups of proteins called the centromere.
  
During Mitosis, mitotic cyclins peak in the cell and trigger kinases, which in turn trigger the breaking apart of the protein bonding the sister chromatids together. One of each chromatid, now called a chromosome, is pulled to each of the new daughter cells, ensuring that they recieve a full copy of DNA. If the sister chromatids fail to separate, they can end up both travelling to the same cell.
  
This results in aneuploid daughters cells, which are cells that do not have the correct amount of chormosomes. These cells often (but not always) cannot function properly because they are either missing genetic information or they have too many copies of certain genes. When genetic information is changed at any point in the cell cycle, this is called a mutation.
  
  This causes the DNA of the cell or daughter cells to change, sometimes by only tiny variations. Though this happens very rarely in regular cells, certain outside chemicals or radiation (called mutagenic factors) can cause mutations. For example, ultraviolet radiation can alter the structure of DNA, and caffeine can accidentally replace certain base pairs. When enough mutations occur to damage both tumor suppressing genes and protooncogenes, which are respectively in charge of regulating cell growth and promoting it, a cell can lose control of how often in divides. This out-of-control cell growth (cancer) can begin to interfere with surrounding tissues and, through metastasis, can spread to other areas of the organism. Given the drawbacks of this condition, it is clear why cells devote so much energy to ensuring that they replicate completely and accurately in the cell cycle.

Your Inner Fish

Though we often hear that all living things are somehow related, this documentary showed how many resulting similarities we have to other organisms. For example, the structure of the bones in our limbs matches that of birds, and even, yes, fish.
  
But that’s not where the similarities end. Human and fish embryos share early forms of gills, the same overall cells, and undescended gonads. But with all these similarities between species, it can be hard to imagine how our differences evolved. This documentary recounted the search for the first organisms to transfer from living underwater to living on land. Eventually, they it revealed Tiktaalik, a transitional flat-headed fish. Like fish, it had scales, fins and gills, but like mammals, it had a neck and lungs. It even matched the skeletal pattern of our limbs today. Other transitional organisms, like the animals between reptiles and mammals, would also share characteristics of both groups of organisms. An animal linking reptiles to mammals might have fur for insulation, but also be cold-blooded. In addition, it may have given live birth. Like both reptiles and mammals, it would have had a backbone. Here’s a drawing of one possible transitional animal: