The earth is about 5 billion years old while the universe is perhaps about 15 billions years old and the earth contains heavy elements that originated from long gone supernovas. Therefore the universe had perhaps three times as much time and far more opportunities than a single planet earth to create life as we know it. Still, many believe that the earth is very special with an ideal sun at the correct heating distance, the right size planet regarding gravity and the ability to hold a protective atmosphere regarding lethal UV light.
I vote for the creation of life on earth but who knows how many distant planets in our galaxy or distant galaxies also succeeded long ago or will far into the future? A leading set of theories are based on the RNA World model. And it was found that RNA molecules, called ribozymes, can catalyze chemical reactions.
In theory, there would be a ribozyme capable of self-replication. Throw in the inaccuracy of replication without proofreading enzymes and you will get variation. Replication and variation lead to evolution. Once you get a self-replication RNA molecule capable of evolving, you have life according to some origin of life researchers. The replicating molecule would probably have to be enclosed in a vesicle of some sort.
A prebiotically plausible vesicle can be made of fatty acids. Jack Szostak has made good progress showing the plausibility of a single-gene protocell. He works with fatty-acid vesicles. The vesicles also contain montmorillonite, which catalyzes the linkage of nucleotides into chains. Szostak has also shown that activated nucleotides can enter the vesicles, but once they are linked together they cannot exit. This provides a means of concentrating nucleotides from the surroundings. Further, he showed that vesicles with more RNA in them "steal" fatty acids from their neighbors, resulting in both competition and growth.
In addition, it has been found that ribose preferentially passes through the fatty-acid membrane of the protocell, helping to explain how ribose could be concentrated from a complex mix of sugars. That's an overview of one leading view. What the heck are scientists thinking, anyways? Teaching opportunities for this episode: Charles Darwin, natural selection, evolution, true love. Students label and define parts of a prokaryotic cell. This page provides links to many biology homework assignments, all currently used, continually tested and refined in live courses.
New assignments are regularly added and updated. Curious stories about what drives scientists! The story of Henrietta Lack's and her immortal cells.
Science will use it to fight cancer and maybe even bring extinct animals back from the dead! Viruses have been downsizing!
What's eating you is smarter than you think! Students are crazy about Radiolab! See what they have to say about the podcast in: Love Letters to Radiolab.
Cell Division - Meiosis. Diagram and describe steps of meiosis starting with six chromosomes. Cell Division - Mitosis. Diagram and describe steps of mitosis starting with six chromosomes. Scientists may someday be able to use it to fight cancer and even resurrect extinct animal. But could tinkering with this biotechnology change the course of human evolution? Prompts students to relate the antiparallel nature of DNA to how it must be copied.
Students define these processes, transcribe a segment of DNA and translate proteins. Students examine their phenotype and possible genotype for several traits of simple inheritance.
Students identify and describe the selective and differential aspects of of two types of specialized growth media from photos. Highlights the relationship between differential bacterial growth media and microbial metabolism.
The Cell Biology chapter of this High School Biology Homework Help course helps students complete their cell biology homework and earn better.
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