Thursday, September 27, 2007

Origin of Life on Earth.... as we know it
Today's lesson focused on the origin of life. To understand the origin of life we must first understand what life is defined as.

Life -- The property or quality that distinguishes living organisms from dead organisms and inanimate matter, manifested in functions such as metabolism, growth, reproduction, response to stimuli, development (change over a lifetime), reproduction, and regulation (homeostasis).

Now that we have the definition of life down, we may proceed to The Origin of Life, or at least the three main hypotheses:
1. Creationism -- Was life created by a supernatural or divine force (i.e.: God). This hypothesis is untestable. (extra information: In 1925, the Scopes Trial ("Monkey Trial") was publicized due to the teaching of Darwin's theory of Evolution in a Tennessee high school by John Scopes. This broke the doctrine which stated that no information which denied the validity of creationism could be taught in public schools. Scopes was found guilty and paid a $100 fine. This law as repealed in 1967.)

2. Extraterrestrial Origin -- The idea that extraterrestrial objects such as meteorites and comets that struck the earth were the original source of organic materials such as carbon. This hypothesis is testable.

3. Spontaneous Abiotic Origin -- Abiotic: meaning non-living. The idea that life spontaneously arose from non-living materials such as inorganic molecules. This hypothesis is testable.

---- Abiotic Synthesis: In 1920 Oparin and Haldane proposed the reducing atmosphere hypothesis in which life originated in an environment that contained less than 1% oxygen and the majority of the atmosphere contained Carbon dioxide. In 1953, Miller and Urey found a way to test this hypothesis: an apparatus. This apparatus simulated early earth environments of which it was believed life formed from. The experiment resulted in that organic compounds such as amino acids, simple sugars, and nucleotides such as adenine (the building blocks of life) were formed. A diagram of this could be seen below:

Origin of Cells:

One theory suggests that the membrane of the cells were developed from lipid-membrane bubbles in that they were easily split into more bubbles, thus creating more cells. These proto-cells separated the inside from the outside (non-polar membrane). These cells preformed metabolism and reproduced.

3.5-2.0 billion years ago Prokaryotes (comprising the bacteria and cyanobacteria, characterized by the absence of a distinct, membrane-bound nucleus or membrane-bound organelles, and by DNA that is not organized into chromosomes) dominated the majority of life on earth. See diagram of ancient fossilized prokaryotes

Stromatolites: fossilized mats of prokaryotes resemble modern microbial colonies see photo below:

Photosyntheic Bacteria: Cyanobacteria, blue-green algae:
-Oxidized the atmosphere. They made aerobic respiration possible.

Eukaryotes: A single-celled or multi cellular organism whose cells contain a distinct membrane-bound nucleus. Developed by enfolding plasma membranes into and around the center going form an oval to a spherical circular. Provided internal micro-environments. The DNA was protected now in the nucleus.

Endosymbiosis: A mutually beneficial relationship in which one organism lives inside the other. This theory, developed by Lynn Margulis, is supported by structures found in modern cells such as mitochondria and chloroplasts that resemble bacterial structure, have their own DNA as does bacteria, move freely within the cell, and reproduce independently from the cell thus giving the illusion that they are separate organisms.

Evolution of Eukaryotes: Mitochondria and Chloroplasts

Mitochondria - cell engulfed aerobic bacteria but did not digest them. Provided a mutual-beneficial relationship.
Chloroplasts - Cell engulfed photosynthetic bacteria but does not digest them. Provided a mutual-beneficial relationship.

Which came first the RNA or the DNA?
RNA is most likely the first genetic material produced in that it has more functions in a cell. It codes information: self replicating, makes inheritance possible, allows for natural selection and evolution. Enzyme functions: robozymes and replication.

Classifying Life

Five Kindoms:

Three Domains ("Super Kingdoms"):
Archaea - (extremophiles-live in extreme enviornments)
Eukarya - Protists, fungi, plants, animals

And heres a few videos for your entertainment:

1942 Fantasia: The Rite of Spring - Part 2: Evolution

This is just a few cartoons put together with evolution parodys. Dilbert, Family Guy, and Simpsons are on it (its the same Simpsons on Kim's post, but the others are pretty good).

-- Shannah

oh and the next sherpa is ............. Maria

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