DNA Replication: The Movie Report

Here is a link to the DNA Replication video that the group made:

https://www.youtube.com/watch?v=4fhPwZePSOU

Though we had read through the DNA Replication chapter in our textbook and even sat through multiple lectures with Mr. Wong about DNA Replication in both Eukaryotes and Prokaryotes, each member of the group learned more about DNA Replication through producing this video.

I think the most difficult concept to grasp from DNA Replication was the concept of the lagging strand. When I first came to class, I knew that DNA on the lagging strand was completed in fragments, but it didn't really understand why and how DNA Polymerase did this. Being forced to model the motion of the protein and track its path delivering and connecting nucleotides to the new strand of DNA after finding an RNA primer, I realized the how the protein's one way system of elongation worked. Because the strands are antiparallel and DNA Polymerase only works from the 5' to the 3' direction, the lagging strand must be broken into fragments to keep up with the splitting of the replication fork by helicase.

Furthermore, I had always wondered why the DNA strand couldn't just be split into two large molecules, the absolute 5' end of each molecule is primed, and then replication occurs, but only in one direction. Then, when I started putting together the fake DNA strands for the video and had to keep track of all the nucleotides and make sure the strand didn't double over or kink, I realized how impossible that split would be floating around in a cell's nucleus. The best way to counteract the kinking and twisting of the molecule would be to keep it together until the last possible moment, then split it and replicate the DNA. This is how cells do it, using replication bubbles instead of breaking up the entire strand of DNA.

I think my group made plenty of mistakes when creating our video, such as not using RNA and DNA Polymerase I to show how RNA primers on the new DNA molecule are removed, but I think that through this process, the entire group now has a mental representation of what DNA Replication must look like and has a concrete experience moving the proteins around. This will help us immensely when thinking critically about DNA problems, and being able to model the process in our minds will far outweigh other students' ability to memorize names and processes.

Your Inner Fish Blog Entry

I was fascinated by the entire Inner Fish program because discovering the links between our distant ancestor species and uncovering more about the human evolutionary history is extremely interesting and gives us a greater understanding of where we came from and why our bodies are shaped the way they are. I think at the beginning of the program I expected an organism like Tiktaalik to be the transitional animal between fish and amphibians: one with strong and flat arms used to kind of shuffle around on land, possessing both gills and lungs, scaled, possessing fins and a fishlike tail, and one that spends most of its time in the water but can also go for periods above water exploring land. I think Tiktaalik is a lot like some modern fish, pikes I believe, that are actually able to do the same thing and climb onto shore and walk around land for a short time. These fish possess both lungs and gills, but their lungs have a very small capacity so therefore they must return to their native water to survive. Though I will never see if this is true or not because evolution takes so long, I think that these types of pike fish could possibly open up another branch of animal evolution.

I think that a transitional animal between reptiles and mammals would look a lot like a crocodile or a lizard with fur. I think that the animal would be partially scaly, but large portions of its body would be covered in fur as most mammals are. The animal would walk on four legs and have short, stubby legs that it must swing from side to side to move forward. Also it would probably be a land based creature, because most mammals do live on land and not in the ocean like dolphins and whales. I believe that the transitional animal would have hardshell eggs, but incubate them internally and then give birth to live young because this is a combination between reptile and mammalian forms of birth. This creature would also produce milk as all mammals do to feed their young. As for the features of the animal, I think it doesn't have a fully articulated neck, but more like a neck that only looks up and down like a crocodile, and have binocular eyes like most mammals, not eyes on each side of its head as some reptiles like the chameleon has. Finally, the animal would have been warm blooded, which is necessary for the internal incubation of eggs as mentioned above. If the animal was cold blooded, the dramatic shifts in temperature could hurt the offspring. Below is a picture of what I think the transitional animal between reptiles and mammals looked like.

The brown areas of the animal represent the fur-covered areas, while the green parts are covered in scales. The animal is very squat and short, and probably moves around in a shuffling run.