On pages 40-44, Dr. Moalem describes how the wood frog survives the harsh winters of its habitat by freezing itself solid. This relates to Big Idea 2, biological systems utilize free energy and molecular building blocks to grow, reproduce, and to maintain dynamic homeostasis because wood frogs utilize glucose to help them resist death from the cold and to maintain homeostasis in the frozen climate.
Explain how the wood frog is able to survive these harsh conditions and how glucose is used to aid this process. In addition, give examples of other organisms that go through this same process. Also, explain the reasons at a molecular level why even though in normal circumstances dehydration is fatal, it can be beneficial in the extreme cold. Finally, explain how we can use this information to help humans in the future.
(Tony Massat tsmassat@mac.com)
The wood frog, Rana sylvatica, has intrigued many scientists due to its ability to survive freezing winter temperatures by freezing itself solid. After the temperatures rise, the frog comes back to life after an almost science-fiction-like state of cryogenic sleep. The biochemical reasons for this survival technique revolve around Big Idea 2, as the frog uses glucose, proteins, and various signals to induce this state.
ReplyDeleteOne of the most dangerous aspects of surviving freezing temperatures is keeping the newly formed ice within the body from damaging organs of cell membranes. The first step after the frog senses the dropping temperatures is to move water out of its blood and organ cells. Any ice within the body is dangerous, but the frog pools the water into the abdomen, where the ice crystals will pose the least danger and the ice may actually have a positive effect.
Another thing the frog does is have the liver dump massive amount of glucose into its bloodstream, pushing its blood sugar level up a hundredfold. This is done because the sugar significantly reduces the freezing point of whatever water remains in the frog’s bloodstream, serving as sugary antifreeze.
Some insects are also capable of this feat. Since water requires a particle such as dust to crystallize, these insects alter their biochemistry and metabolism to clear the gut of lipoprotein nucleators. Like the frog, these insects are able to survive cold temperatures by altering their biochemistry to maintain homeostasis (Big Idea 2). A National Geographic Article (http://news.nationalgeographic.com/news/2005/03/0301_050301_woodfrog_2.html) explores this idea further. It states that besides the insect species that can withstand freezing temperatures are also “six North American frog species, one European lizard, and a handful of North American turtles”. The article also explains that one day, this ability may be observed in a number of Asian animal species.
Anyone that has been out on a hot day without water knows that dehydration is detrimental to overall health. This is true for a typical metabolism, but the case of the frog changes things. We learned early in the year that water serves many purposes, one of which is to keep the body cool in hot temperatures (i.e. sweat), but this is clearly of no use in freezing temperatures. And since the frog is basically frozen solid and doesn’t conduct any metabolic processes for the duration of the winter, it does not need water in the same way that we need water. While enduring freezing temperatures, the frog benefits from dehydration because it does not need water for its metabolism and the removal of water reduces the chance that ice crystals formed within its body cause damage to tissue, organs, or cell membranes.
The frog is basically freezing its organs and after a while, they are thawed and fully functional. How can figuring out how to keep organs functional for a long period of time while frozen be beneficial to us humans? According to organdonor.gov, an average of 18 people die each day because they can’t receive an organ transplant on time. If we are able to figure out how the wood frog is able to keep its organs functional after months of being frozen, we may be able to apply it to human organ transplants so that organs are given to people that need them in time. Many people do not get organ transplant in time because “a human kidney can be preserved for just two days outside the human body, while a heart can last only a few hours” (Moalem 42). We don’t know how to keep human organs frozen and functional for long periods of time, but the wood frog has the same major organs as humans, making it a good candidate for figuring out how to keep organs functional, a “huge breakthrough that could save thousands of lives each year” (Moalem 42).
(Mikhail Iouchkov mikhailiouchkov@gmail.com)