DNA Replication

1. Initiation

• Helicase unwinds the DNA and starts separating the strands.
• Single-Strand Binding proteins hold the strands in place and prevent them from coming back together
• Gryase cuts the DNA into smaller parts to prevent the tension from building up
• Primase place RNA Primers to signal Polymerase III to start making the replicated strand.

2. Elongation

• Polymerase III creates the replicated strand in the 5' to 3' direction.
  • The leading strand is done continuously (it is being unzipped in the 3' to 5' direction so the new strand can be created in the 5' to 3' direction without any breaks
  • The 'lagging' strand needs to be replicated in the opposite direction so it is done in sections called Okazaki Fragments.
• RNA Primase starts off each Okazaki Fragment and Polymerase III follows. Each Okazaki Fragment is approximately 100-200 nucleotides long

3. Termination

• Polymerase I 'proofreads' the replicated strand and corrects any errors. It also removes the RNA Primers and replaces them with Deoxyribonucleotides.
• Ligase forms Phosphodiester bonds between the Okazaki Fragments to hold them together.

Photosynthesis and Cellular Respiration Activity

In class we did a group activity, in which each group had to make a three-dimensional representation of one process of cellular respiration or photosynthesis. Our group was responsible for the non-cyclic electron transport chain in photosynthesis, which is pictured last. Following are all the models:

The ROM (and the Gairdner Symposium)

This Halloween, our class had the privilege of attending the Gairdner Symposium at the University of Toronto, where we were given speeches by recipients of the award about their lives with science. However, as interesting as that was, this blog post is about the tour of the ROM we had the opportunity to partake in following the presentation. We were led by a very knowledgeable and interesting tour guide who did a very good job explaining each exhibit and its significance. One in particular which stuck in my mind was one about the Arctic Fox and its main food source, the lemmings.

At first glance, the case shows what seems to be an unsurprising or relatively insignificant - An Arctic Fox with a minuscule lemming limply dangling from its jaw. "Okay," you might think, "What's so special about that?"

At least, that's what I thought when I looked at the display case before our tour guide started explaining the special, albeit delicate predator-prey relationship the Arctic Fox shares with the lemming. The entire basis of population dynamics is that populations of all species are interconnected in some way, and a slight fluctuation in one can affect the other in sometimes unpredictable ways. It's pretty difficult to demonstrate this idea better than the Arctic Fox.

Lemmings have what's known as a "boom and bust" population cycle - their population size fluctuates immensely. They have been known to go from exorbitant population sizes to near extinction in the span of a few generations. In fact, people have speculated that they might even commit suicide to give their species a better chance at survival (but this idea was faulty in many aspects).

Instead, what controls their population size is the carrying capacity - the maximum number of individuals that can survive in the given space with the given amount of resources. When population sizes start getting our of control, food and space becomes scarce, disease rates ramp up, and predators become more abundant due to an increase in the amount of available food - this is where the Arctic Fox comes in. Over time, the sizes of both the populations have been observed to have a strong correlation with each other. When the lemmings go through a "boom" phase, or have large numbers, the Arctic foxes will also have large litter sizes that year, and vice-versa for when the lemmings go through a "bust."

This is just a small aspect of population dynamics, but does a very good job in demonstrating how different species are interconnected in complicated, yet delicate ways. The main idea that the guide wanted us to walk away with after that presentation was that scientists have to consider every single aspect of a species' life before they can take any sort of action (like a conservation effort). This can often be difficult because of all the possible factors that can be present and have an effect in their lives.

Overall, the ROM was a positive experience which I took away a lot from. We covered a lot of different topics throughout the tour, including parasitic flowers smelling like rotten meat¹, how humans drove the most abundant bird species to complete extinction², fish that explode when caught³, and of course, dinosaur skeletons.

¹ Rafflesia
² Passenger Pigeon
³ Deep sea fish (like the angler fish)