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Chapter 3

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Wilfrid Laurier University
Matthew Smith

 3.1 - What is Life?  Characteristics of life are emergent  Emergent since characteristics arise from many simple interactions  7 Characteristics of Life  Display order  Arrangement (i.e. flower petals)  Harness and utilize energy  All life acquires energy from environment and uses it to maintain order  Reproduce  Respond to stimuli  Organisms able to adjust themselves (i.e. structure, function, behaviour, etc.) in response to environment  Exhibit homeostasis  Ability to regulate internal environment  Growth and development  Evolve  3.2 - The Chemical Origins of Life  Earth is 4.6 billion years old  Life evolved on Earth since Sun is far away enough that water can remain in liquid state  Earth within habitable zone of solar system  Biologically important molecules can be synthesized outside of living cells  Hypothesis 1: Reducing Atmosphere  Abundance of water vapour in primordial atmosphere due to abundance of hydrogen, carbon dioxide, ammonia, and methane (oxygen almost nonexistent)  Oparin and Haldane suggested that organic molecules could've formed in primordial atmosphere  Key --> early atmosphere was reducing atmosphere (due to large amts. of hydrogen, methane, ammonia); such molecules contain many electrons and hydrogen  Today's atmosphere is oxidizing atmosphere; high levels of oxygen present; oxygen accepts large amounts of electrons and is reduced to water  No ozone in primordial atmosphere (no oxygen); thus UV rays able to reach Earth in large amts. as well as lots of lightning which provided plenty of energy for formation of organic molecules  Miller-Urey Experiment put the Oparin-Haldane hypothesis to the test  Experiment demonstrated that abiotic synthesis of biologically important molecules is possible  Polymers such as proteins and nucleic acids not produced; though that polymerization reactions can occur on solid surface such as clay  Hypothesis 2: Deep-Sea Vents  Organic molecules could've originated on ocean floor in deep-sea (hydrothermal) vents  Cracks found near sites of volcanic/tectonic activity and release superheated nutrient-rich water at temp. greater than 300 degrees Celsius, as well as reduced molecules including methane, ammonia, and hydrogen sulfide  Many of these life forms able to thrive under great pressure and in absence of light  Hypothesis 3: Extraterrestrial Origins  Organic molecules came from space  500+ meteorites collide w/ Earth each year; meteorites composed of carbonaceous chondrites (rich in organic molecules)  Murchison meteorite contains biologically important molecules such as various amino acids (i.e. glycine, glutamic acid, alanine) as well as purines and pyramidines  3.3 - From Macromolecules to Life  Protobiont --> group of abiotically-synthesized organic molecules that are surrounded by membrane or membrane-like structure  Liposome --> lipid vesicle where lipid molecules form a bilayer similar to cell membrane; are selectively permeable; form spontaneously  May have been first membrane-bound compartment that developed into first cells  Central dogma  DNA ---(transcription)---> RNA ---(translation)---> Protein  Ribozymes --> group of RNA molecules capable of catalyzing specific reactions; since they can
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