This unit is designed for High School Chemistry students, which usually includes 10 th, 11 th, and 12 th graders. It is designed to extrapolate an entire year's worth of engaging, hands-on activities from the three foundational experiments in this unit, with the students becoming 'master high school chemists' by year's end. By using the repetition of materials and procedures from experiments, there will be an added benefit to the teacher of minimal preparation time, as well as minimal cleanup time, since the students will gradually take on more responsibility for this part of the process. By focusing on everyday life products such as diesel, soap, gasoline, and clean water that are all created from 'everyday items', students will be able to relate the value of Chemistry in 'Everyday Things'.
The topic of clean water (or lack thereof) is a well researched issue that is critical for our survival. Although the social issues caused by lack of clean drinking water are beyond the scope of this unit, the overarching problem must be addressed with students who are most likely unaware that a problem even exists. As one panel with the National Science Foundation put it,
Our community has just been hit with a major hurricane. Support services are limited and you and your team (class) have been commissioned to assist in the recovery of vital services. Using materials that you find within your neighborhood, the classroom, construct a biodiesel processing unit, a bioethanol processing unit, and a water purification, filtration, and distillation system. You will be given valuable raw materials (1 knorr's jar of waste vegetable oil, 1 knorr's jar of river or rain water, 2 ounces of yeast, 2.25 kg of sugar, and 2.25 kg of corn meal). Besides building the processing units, you must create 1 clean knorr's jar worth of distilled, purified, and filtered drinking water, 1 jar of biodiesel, and 1 jar of bioethanol). The timeframe to complete the project is 2 weeks. Good Luck. Our survival depends on this.
"Green Chemistry | US EPA." U.S. Environmental Protection Agency. (accessed July 13, 2009). This is the EPA's website regarding Green Chemistry. It is a great resource for teachers with links to activities and literature regarding sustainability and green chemistry initiatives.
How life on Earth began remains an unexplained scientific problem. This problem is nuanced in its practical details and the way attempted explanations feedback with questions and developments in other areas of science, including astronomy, biology, and planetary science. Prebiotic chemistry attempts to address this issue theoretically, experimentally, and observationally. The ease of formation of bioorganic compounds under plausible prebiotic conditions suggests that these molecules were present in the primitive terrestrial environment. In addition to synthesis in the Earth's primordial atmosphere and oceans, it is likely that the infall of comets, meteorites, and interplanetary dust particles, as well as submarine hydrothermal vent synthesis, may have contributed to prebiotic organic evolution. The primordial organic soup may have been quite complex, but it did not likely include all of the compounds found in modern organisms. Regardless of their origin, organic compounds would need to be concentrated and complexified by environmental mechanisms. While this review is by no means exhaustive, many of the issues central to the state of the art of prebiotic chemistry are reviewed here.
The origin of life remains unexplained despite decades (or perhaps centuries, depending on where one historically marks the starting point) of research. A considerable amount of study has provided compelling details as to how it might have occurred and whether it is likely to be a universal phenomenon. The development of modern thought on the topic has a long and winding history and has been modified to adapt to developments in other fields, including astronomy, biology, chemistry, and geology. This review covers the synthesis of small organic compounds; however, it should be borne in mind that the major uncertainties revolve around how these compounds self-organize into self-replicating systems.
Coincidentally, Watson and Crick published their structure for the DNA double helix within a week of the publication of Miller's results (Watson and Crick 1953). Until that time, it had been widely debated whether proteins or nucleic acids were the carriers of genetic inheritance (though the evidence was strongly in favor of the latter): the structure of DNA left little doubt. This close historical juxtaposition of discoveries reveals a common motif in prebiotic chemistry and in origins-of-life models in general: discoveries in other fields frequently drive advances in origin of life models.
Some analyses of this tree suggest hyperthermophilic archaebacteria are the oldest organisms on Earth (Wang et al. 2007), which has been used to argue that the types of environments these organisms inhabit presently were the earliest environments for life and thus likely sites of the origin of life. This idea remains controversial (Arrhenius et al. 1999; Gupta 2000). The reconstructed tree suggests that the Last Universal Common Ancestor (LUCA) of all modern biology was a single-celled prokaryote, albeit one with an already sophisticated and very modern biochemistry, suggesting a prior protracted period of biochemical evolution.
A variety of organic compounds have been identified in CCs, including many found in modern biochemistry (Pizzarello et al. 2006). That these compounds are indigenous to the meteorites, and not terrestrial contamination, is suggested by the facts that they have unusual isotopic ratios and include types of compounds not typically found in biochemistry; and that compounds with stereocenters are found in nearly equal quantities with respect to their optical isomers, with some notable exceptions (Pizzarello and Cronin 2000; Glavin and Dworkin 2009). A brief summary of the types and relative abundances of compounds identified to date is shown in Table 2.
We do not know which compounds were required for the origin of life. Prebiotic chemists tend to focus on compounds which are present in modern biochemistry, ignoring the large fraction of compounds found in meteorites or produced in simulations that are not found in biology. A recent study of the Murchison CC using sophisticated analytical instruments revealed the presence of many as around 14 million distinct low molecular weight organic compounds (Schmitt-Kopplin et al. 2010). This can be contrasted with the approximately 1,500 common metabolites found in contemporary cells (Morowitz 1979) and the some 600 small molecules positively identified in the Murchison meteorite to date (Table 2).
The Murchison CC contains small amounts of straight-chain fatty acids, though some of these may be contamination (Yuen and Kvenvolden 1973). Amphiphilic components have been observed in the Murchison meteorite and in various laboratory simulations of prebiotic chemistry (Dworkin et al. 2001) (Fig. 5c), though the composition of these remains undetermined.
Additionally, when aqueous solutions of HCN and HCHO are mixed, the major product is glycolonitrile (Schlesinger and Miller 1973), which could preclude the formation of sugars and purines in the same location (Arrhenius et al. 1994). Nevertheless, both sugar derivatives and nucleic acid bases have been found in the Murchison meteorite (Cooper et al. 2001; Callahan et al. 2011), and it seems likely that the chemistry which produced the compounds found in Murchison meteorite was from aqueous reactions of simple species such as HCN and HCHO. This suggests that the synthesis of sugars, amino acids, and purines from HCHO and HCN may take place under certain conditions.
The difficulties with prebiotic ribose synthesis and nucleoside formation have led some to speculate that perhaps a simpler genetic molecule with a more robust prebiotic synthesis preceded RNA (Joyce et al. 1987). Substituting sugars besides ribose has been proposed (Eschenmoser 2004). Oligomers of some of these also form stable base-paired structures with both RNA/DNA and themselves, opening the possibility of genetic takeover from a precursor polymer to RNA/DNA. Such molecules may suffer from the same drawbacks as RNA with respect to prebiotic chemistry, such as the difficulty of selective sugar synthesis, sugar instability, and the difficulty of nucleoside formation. It has been demonstrated based on the suggestion of Joyce et al. (1987) and proposed chemistry (Nelsestuen 1980; Tohidi and Orgel 1989) that backbones based on acyclic nucleoside analogs may be more easily obtained under reasonable prebiotic conditions, for example by the reaction of nucleobases with acrolein obtained from mixed formose reactions (Cleaves 2002).
Whether in meteorites or on Earth, prebiotic chemistry may have occurred largely in an aqueous environment, as water is a ubiquitous component of the solar system and the Earth's surface. Among the variables of the local environment which could affect the way this chemistry occurs are pH, temperature, inorganic compounds such as metals, mineral surfaces, the impact of sunlight, etc. The potential role of mineral surfaces on prebiotic chemistry is an especially complex and under-explored aspect of this chemistry. Although we do not presently know which compounds were essential for the origin of life, it seems possible to preclude certain environments if even fairly simple organic compounds were involved (Cleaves and Chalmers 2004).
Proceeding outward from the Sun, complex organic chemistry likely occurs in the atmospheres of Saturn and Jupiter. The conditions on the solid surfaces of these planets are thought to be too hostile for more complex organic chemistry. Nevertheless, the presence of various organic species has been confirmed in their atmospheres (Lodders 2010).
A number of outer-planet moons have intriguing environments which appear to foster prebiotic chemistry and could conceivably be capable of sustaining biology. For example, Saturn's moon Titan is now known to harbor a rich organic chemistry (Waite et al. 2007). Jupiter's moon Europa is covered with a thick ice layer which may harbor a watery ocean several kilometers thick (Manga and Wang 2007). If this ocean does exist, its organic content remains unknown. 2b1af7f3a8