1.5 The origin of cells

Cellular origins The cell theory dictates three things: The cell is the most basic unit of life. All organisms are made of one or more cells. All cells come from pre-existing, living cells. Wait….if all cells came from pre-existing cells, then where did the first cell come from? ????? If we can trace that zygote back to the sex cells that our parents produced, and we can trace the origin of all the cells in their bodies back to the cells in their parents bodies……etc. etc. and so forth, why can’t we just go back to the first life form?

Cellular origins Louis Pasteur – scientist in the 1800s hypothesized about the origin of life Humans thought for many years that life had spontaneously come about, out of nothing. This guy performed a series of experiments to prove that spontaneous generation of organisms does not still occur on Earth. Using these

Experimental setup Pasteur found that nutrient broth in a sealed flask would remain unchanged, whereas nutrient broth when exposed to air, would show bacterial growth This proved that cells only come from pre-existing cells

A logical conclusion Assuming aliens are not the source of life on the planet, life must have arose from non-living material 4 Stages: Production of carbon compounds, such as sugars and amino acids Assembly of carbon compound polymers Formation of membranes Development of a mechanism for inheritance 1 st Stage 2 nd Stage 3 rd Stage4 th Stage

1. Production of Carbon compounds 1. Organic compounds introduced 2. Organic Compounds heated 3. Electricity run through organic compounds as a vapor 4. Water condensed and sampled Scientists hypothesized that using the building blocks of organic matter, organic compounds could be induced to be created

Check out this video in order to be able to answer the following questions : What was the goal of the Miller-Urey Experiment? What evidence did the Miller-Urey Experiment provide against the theory of Spontaneous Generation? What were the discoveries of this experiment?

2. Assembly of carbon compounds into polymers Polymer – multi-unit molecule, consisting of two or more repeating parts Hydrothermal vents – provide surplus of energy in form of heat, and reagents in the form of chemicals Yay – Attenborough! 71 In what way are the modern hydrothermal vents analogous to the ancient atmosphere? How do the organisms get their energy?

3. Formation of membranes If phospholipids were among some of the carbon compounds created, then they would naturally form into a bilayer membrane due to it being the most energy-favorable position for them These membranes would allow for a different chemistry to be created internally as compared to the surroundings Liposomes in 3D configuration Liposome formation video

4. Development of a mechanism for inheritance Cells originally only possessed RNA, which can replicate itself and act as its own catalyst for the process of replication. It would not be until much later that DNA was in use in cells, due to the fact that it needs much more complex mechanisms for its replication and operation

Endosymbiosis = “within” + “mutually beneficial relationship” The origin of eukaryotic cells can be explained by the endosymbiotic theory. This states that mitochondria and chloroplast were once separate individual organisms, which were engulfed by larger prokaryotic organisms Which type of cells did human cells come from?

Inquiry Activity – Endosymbiotic Theory Your Task – To prove whether the endosymbiosis of mitochondria and chloroplast is worth or not. Determine the following: Benefit to eukaryotic cells Benefit to mitochondria Benefit to chloroplast Detriments to any of the above elements Compose your argument in a brief argumentative statement to the following, based on your research: Was the endosymbiosis of chloroplast and mitochondria worth for eukaryotic cells? Was it more beneficial to larger organisms or smaller organisms? Finally, respond to the following statement: Animal cells are more evolved than plant cells. Use your research to either agree or disagree with the above statement. Why is it mutually beneficial? ? ? ? ? ? ?