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Bio1140 D.Johnson Notes.docx

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Department
Biology
Course Code
BIO1140
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A L L

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Chapter 2Origins of life21What is life The types of atoms and molecules found in living things are no different from those found in nonliving forms of matter living cells obey the same fundamental laws of chemistry and physics as does the abiotic nonliving worldthe biochemical reactions that take place within living cells although seemingly remarkably complex are only modifications of reactions that take place in the abiotic world21aSeven characteristics that all forms of life shareall forms of life share a set of attributes that collectively differentiate them from nonliving thingseven fundamental characteristics that are common to all forms of lifeoDisplay order all forms of life are arranged in a highly ordered manner with the cell being the fundamental unit of lifeoHarness and utilize energy all forms of life acquire energy from the environment and use it to maintain their highly ordered stateoReproduce all organisms have the ability to make more of their own kindoRespond to stimuli organisms can make adjustments to their structure functions and behaviour in response to changes to the external environmentoExhibit homeostasis organisms are able to regulate their internal environment such that conditions remain relatively constantoGrowth and development all organisms increase their size by increasing the size andor number of cellsoEvolve populations of living organisms change over the course of generations to become better adapted to their environmentIs a virus aliveA handful of biological entities straddle the definition of life and the best example of these is a virus Viruses seemingly display many of the properties of life including the ability to reproduce and evolve over timethe characteristics of life that a virus possesses are based on its ability to infect living cellsAlthough viruses contain nucleic acids they lack the cellular machinery to synthesize their own proteinsFor this reason most scientists do not consider a virus alive21bThe fundamental unit of life is the cellcell theoryoAll organisms are composed of one or more cells in unicellular organisms the one cell is a functionally independent organism capable of carrying out all life activitiesIn more complex multicellular organisms including plants and animals major life activities are divided among varying numbers of specialized cellsoThe cell is the smallest unit that has the properties of life If cells are broken open the property of life is lost they are unable to grow reproduce or respond to outside stimuli in a coordinated potentially independent fashionoCells arise only from the growth and division of preexisting cells Although deoxyribonucleic acid DNA and ribonucleic acid RNA contain the information required to manufacture a vast array of biological molecules they cannot orchestrate the formation of an entire cell New cells can arise only from the division of preexisting cells22the chemical origins of lifebeen a time when no cells existed when there was no lifecells with the characteristics of life arose out of a mixture of molecules that existed on the primordial Earth22bconditions of primordial earthEvidence using a range of dating methods has firmly established that Earth the Sun and the other planets of the solar system all formed at about the same time According to the most widely accepted hypothesis the solar system was formed by the gravitational condensation of matter present in a molecular cloud which initially consisted mostly of hydrogen Intense heat and pressure generated in the central region of the cloud formed the Sun whereas the remainder of the spiralling dust and gas condensed into the planetsOnce Earth was formed its early history was marked by bombardment of rock from the stillforming solar system and extensive volcanic and seismic activityOver time Earth radiated away some of its heat and surface layers cooled and solidified into the rocks of the crust Because of its size Earths gravitational pull was strong enough to hold an atmosphere around the planetThe primordial atmosphere probably contained an abundance of water vapour from the evaporation of water at the surface as well as large quantities of hydrogen sulphide HS carbon dioxide CO ammonia NH and methane CH2234Some of these compounds were formed spontaneously by reactions in the atmosphere whereas others were the result of volcanic eruptions From these basic building blocks the molecules essential to the formation of life are thought to have formed22cThe MillerUrey ExperimentThe lack of oxygen in the primordial atmosphere meant that there was no ozone O 3layer to partially block the Suns energetic ultraviolet light from reaching Earths surface Stanley Miller a graduate student of Harold Urey at the University of Chicago created a laboratory simulation of the reducing atmosphere believed to have existed on early Earth Miller placed components of a reducing atmospherehydrogen methane ammonia and water vapourin a closed apparatus and exposed the gases to an energy source in the form of continuously sparking electrodesWater vapour was added to the atmosphere in one part of the apparatus and subsequently condensed back into water by cooling in another partMiller found a large assortment of organic compounds in the water including urea amino acids and lactic formic and acetic acidsWhen HCN and CHO molecules were added all the building blocks of complex 2biological molecules were producedamino acids fatty acids the purine and pyrimidine building blocks of nucleic acids sugars such as glyceraldehyde ribose glucose and fructose and phospholipids which form the lipid bilayers of biological membranes22dthe synthesis of polymers from monomerskey building blocks of life such as nucleic acids and proteins are not individually synthesized molecules called monomersInstead they are macromolecules built up from large numbers of subunit monomers coming together to produce what are called polymers
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