Hypotheses of Life's Origin

Blog 1.D.1 and 1.D.2

Hypothesis of Life’s Origin
Kelly Nienburg, AP Biology P.4
October 16, 2014


Today we'll be talking about several popular hypotheses of how life on earth came
to be. I hope y'all learn something. :)

The earth was first predicted, in 1897, to be between 20 and 40 million years old. But even 40 million years was not enough time for the level of evolution that the earth has.

It was determined in 1956 by radiometric dating on meteorites that the earth is approximately 4.5 billion years old. The earth was also unsuitable for life for the first half a billion years it was formed because it was essentially a molten ball of lava and toxic gasses.

It took half a million years for the earth to cool down enough and produce water. But how did life come along? Well, there are many hypotheses about how life on Earth came to be. 

One of the most famous is the “Organic Soup Model,” which shows how with water with only nutrients and gases that were thought to cover early Earth, organic compounds were formed. These compounds are the basics of genetic material that all life contains.

Another popular hypothesis is that a meteor brought organic compounds and amino acids to earth.  What makes this possible is that in Australia, an asteroid rich in organic compounds and containing 70 amino acids and nucleotide bases was discovered.

These organic molecules combines with Earth’s inorganic precursors could have, in both cases, synthesized with all the free energy available and became monomers. The absence of a large amount of oxygen helped also.

These monomers then joined and formed into more complex molecules called polymers, including nucleotides and amino acids. These new polymers had the ability to reproduce, store and transfer information, like ones in current organisms’ cells.

Soon enough, these polymers were packaged into probionts, which were what could be called the first cell-like things, as they had fatty membranes. These probionts then formed into liposomes, which contained the first lipid bilayers when added to water. This membrane was semi-permeable.

The RNA World Hypothesis proposes that RNA may have been the planet’s earliest genetic material, as it essentially runs protein synthesis and even has enzyme-like functions. RNA later on provides the foundation for DNA.

The oldest fossils knows were made of many layers of bacteria and sediment. They are called Stomatolites. These bacteria were autotrophic and some photosynthetic. These prokaryotes were the only known life form on earth for about 1.5 bya. These photosynthetic bacteria created a ton of oxygen, which caused many species of prokaryotes to become extinct. One of these kinds of bacteria are the LCA, or last known common ancestor to all life.

The first eukaryotic cells came into existence around 2.1-2.7 bya. They were a sort of chimera of an aerobic heterotroph and a host cell. The ancestors to what we know today as Mitochondria and Chloroplasts entered the cell. Plastids came about to be inside the cell later on. These allowed the new cells to metabolize energy.

Next came multicellular prokaryotes, around 1.5 bya after the first eukaryotes were formed. After these first formed, these cells began to evolve into eukaryotic animals, known as the Cambrian period. Autotrophic bacteria evolved, forming a waterproof wax coating to prevent desiccation, roots, spores to protect them from radiation, a vascular system to transfer water and nutrients through the plant from the roots and tough cells for support(stems); all of these allowed for the colonization of land by plants. Animals soon evolved their own mutations and were able to populate the land soon after the plants.

And that's how life most likely came to be! :)

Citations:
http://resources0.news.com.au/images/2011/08/10/1226112/560528-meteorite-dna.jpg
https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh66GOEK2oAi-H3IU-WRWlxvAvBNPs7jC67DS7CJlGpby5TZ2PFYlmtlZLOknJqqCLznmVapkGj6mhADTa4b4WOe7fw6-9i2Wn8-Nt9L6qQnTHXU_FtBMqN15pJVCpx77oRe0esnrTxm-M/s1600-h/Miller-Urey_experiment_svg.png
http://media-2.web.britannica.com/eb-media/01/123001-004-2FC93D97.jpg
http://www.rsc.org/images/wochner1HR_410_tcm18-200601.jpg

http://whyevolutionistrue.files.wordpress.com/2011/08/fossil-stromatolite.jpeg
http://upload.wikimedia.org/wikipedia/commons/e/e8/Frangula_alnus_with_magnesium_deficiency.jpg

http://www.mlhi.org/science/period2/Period2_files/image007.gif

Part 1.C.1 - 1.C.2

1.C.1: Speciation and extinction

First, let’s talk about what we know as speciation and extinction. I’m sure we all know what extinctions, because honestly, what idiot HASN’T heard about the extinction of the dinosaurs billions of years ago? Okay that was mean and I’m certain that there are other homo sapiens that haven’t had the education and luck to be as informed as you and I, but that’s beside the point! The point is, extinction means the eradication of a species. Which means once the last organism of that species dies, then that species is gone for good. Inexistent.

Speciation is exactly the opposite- speciation is the phenomenon that occurs when species evolve from old species (who eventually die off). Something called Adaptive radiation helps this along. Adaptive radiation occurs when other species or populations disappear from an ecosystem and surviving species evolve and replace those that once lived there. For example, when the dinosaurs went extinct, mammals – who were rodent-like creatures at that time – were able to evolve many times over and eventually replace them.

What does it mean to evolve? Evolving, better known as evolution, is the process of organisms changing into new organisms (species) by random mutations in their DNA. Every organism that ever existed has existed because of evolution from one ancestor, billions of years ago. And all organisms that have yet to exist will exist because of evolution. Isn’t that interesting?

 Speciation is also the origination of biodiversity

1.C.2: Reproductive Isolation

Reproductive isolation is the phenomenon that prevents organisms of separate species species from producing fertile offspring. Either they produce sterile hybrids, or will not, due to species specific mating rituals, reproduce.

There is also mechanical isolation in which the genitals will not match up between the organisms to fertilize a gamete.

Pre-zygotic barriers prevent the fertilization of an egg, and post-zygotic barriers ensure the organism can not reproduce or dies before it reaches sexual maturity.

1.C.3: Populations Evolve

Now let’s talk about how populations evolve.

When an organism develops a mutation in its DNA, there are several things that can happen. One is that it could have absolutely no effect, having changed a nucleotide in a codon to one that codes for the same nucleic acid. An example would be changing a CGU to a CGA, both of which codes for Arginine and therefore will not affect the organism physically. If this happened to turn CGU, for example, into GGU, then it would code for Cysteine instead of Arginine. This could change a characteristic of the organism for better or worse. An insertion (adding in a polypeptide that wasn’t there before)or a deletion (the accidental removing of a polypeptide during the copying of the RNA or DNA) of a nucleotide in the DNA could potentially destroy an organism or create a new species, as it would change all DNA after the insertion or deletion.

This image is a codon chart^ All DNA and RNA are made to code for these amino acids.

But anyways, when organisms and the population they live in evolve they survive if they have favorable (fit) traits that give them the survival advantage for their environment. They then reproduce with others in the population and form a separate species.  For example, if a population of aphids were sprayed with a pesticide and a dozen had a genetic advantage (an evolved trait) that allowed them to survive, they would reproduce and therefore be fit. This is an example of adaptive evolution.

Citations:

http://www.greenrootslandscaping.com/wp-content/uploads/2014/04/aphids.jpg

Kelly Nienburg - Period 04 - AP Biology

All About Phylogenetic Trees

First… What is a Phylogenetic Tree, exactly?

The word combination Phylogenetic Tree is derived from the word “phylogeny,” which means the evolutionary history of a group or species. The “tree” part is added because the chart somewhat resembles a tree.

A phylogenetic tree, also known as a genetic tree, is a branching diagram showing chronological, evolutionary relationships between organisms and their ancestors. Phylogenetic trees are models of hypotheses of evolutionary history.

https://www.youtube.com/watch?v=fQwI90bkJl4
^Bozeman video on Phylogenetic Trees
Taxonomy, which also helps to organize species into phylogenetic trees, is the organization of organisms into categories. Species are organized by a method called hierarchical classification. The organisms are organized by the words below, with Domain being the broadest category and species the most specific:

“Dreadful King Phillip Came Over From Great Spain” is a good way to remember how to organize these words!

 

How is a phylogenetic tree organized?

It is organized based on some of their physical and genetic traits (DNA). Also, where the organism was discovered. The taxa joined in the tree are said to have descended from a common ancestor. They are put into categories showing their relation to other organisms, either ancestral or descendent.

https://www.youtube.com/watch?v=bILvTe2_FEE

Bozeman video of how organisms are classified and organized^

In a lab we recently did, we had to guess where an unknown fossil went in an example of a phylogenetic tree. We went onto a website and compared its DNA sequences to that of modern day organisms. Through those comparisons and observations, each of us decided where the organism belonged, based on relation to each animal its DNA was compared to.

Citations:

PowerPoint for Phylogenetic Trees

www.dictionary.com

http://www.wiley.com/college/pratt/0471393878/instructor/activities/phylogenetic_trees/index.html
https://bioweb.uwlax.edu/bio203/s2013/phillips_reb2/classification.htm