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Lecture 2

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Biological Sciences

Lecture 2 + 4 + 6 (Chapter 2) ORIGINS OF LIFE - There are 7 characteristics that all forms of life share: 1) DISPLAY ORDER, all forms of life consists of organized cells. 2) HARNESS AND UTILIZE ENERGY, all forms of life acquires energy from the environment and uses it to maintain their biological function. 3) REPRODUCE, all organisms have the ability to make more of their won kind. 4) RESPOND TO STIMULI, organisms can make adjustment to their structures, function, and behaviour in response to changes to the external environment. 5) MAINTAIN HOMEOSTASIS, organisms are able to regulate their internal environment such that conditions remain relatively constant. 6) SHOW GROWTH and DEVELOPMENT, all organisms increase their size by increasing the size and/or number of cells. 7) EVOLVE, populations of living organisms change over the course of generations to become better adapted to their environment. - Viruses are not considered a form of life because they lack the cellular machinery to synthesize their own proteins. They have to highjack the machinery and metabolism of a living cell in order to reproduce. - CELL THEORY: 1) All organisms are composed of one or more cell. 2) The cell is the smallest unit that has the properties of life. 3) Cells arise only from the growth and division of pre-existing cells. CONDITIONS ON PRIMORDIAL EARTH - Bombardment of rock from still forming solar system and extensive volcanic and seismic activity. - Earth radiated some of its heat and surface layers cooled and solidified into the rocks of the crust. - Because of its size, Earth’s gravitational pull was strong enough to hold an atmosphere around the planet. - Primordial atmosphere contained an abundance of water vapour from the evaporation of water at the surface, and large amount of hydrogen sulphide (H2S), carbon dioxide (CO2), ammonia (NH3), and methane (CH4), which are basic building blocks for formation of life. - Compounds were formed by reactions in the atmosphere and volcanic eruptions. - Organic molecules such as amino acids, sugar, and the nucleotide bases that form DNA and RNA are essential to the formation of life and could have been made in the absence of life (abiotic synthesis) - Early atmosphere was a reducing atmosphere because of the high concentration of molecules such as hydrogen (H2), methane and ammonia. - Today’s atmosphere is an oxidizing atmosphere because of the presence of O2 (strong oxidizing molecule). THE MILLER-UREY EXPRIMENT - Primordial atmosphere = lack of oxygen = no ozone (O3) layer to block sun’s ultraviolet light. - Ultraviolet light + lighting provided the energy that combined with the reducing conditions present in the atmosphere  accumulation of the simple “building blocks” required for life. - STANLEY MILLER, created a simulation of the reducing atmosphere. Miller placed components of a reducing atmosphere (hydrogen, methane, ammonia, and water vapour) in a closed apparatus and exposed the gases to an energy source in the form of continuous sparking electrodes. Water vapour was added at one part and condensed back into water by cooling another part. - MILLER found all sorts of organic compounds in the water, including urea, amino acids and lactic, formic, and acetic acid. 15% of carbon in methane was converted to organic compound. - When HCN and CH2O molecules were added to the simulated atmosphere in Miller’s apparatus, all building blocks of complex molecules were produced (amino acids, fatty acids, and the purine and pyrimidine building blocks of nucleic acids, sugar such as glyceraldehydes, ribose, glucose, and fructose, and phospholipids, which forms the lipid bilayers of biological membrane.) THE SYNTHESIS OF POLYMERS FROM MONOMERS - Nucleic acids and proteins are not individually synthesized molecules, called monomers. They are macromolecules, built up from large numbers of subunit monomers coming together to produce what are called polymers. - Nucleic acids are polymers of nucleotides, proteins are polymers of amino acids, and carbohydrates are polymers of simple sugar. - Polymerization: joining of monomers together into polymers. PROTOBIONTS: THE FIRST CELL - A protobiont: a group of ABIOTICALLY produced organic molecules that are surrounded by a membrane or membrane-like structure. - Protobiont is important because it allowed for an internal environment to develop that was distinctly different from the external environment: the concentration of key molecules could be higher, and molecules could attain more order in a closed space. - Protobionts could have formed spontaneously from abiotically produced organic compound. - Protobionts were produced in the lab - Have small membrane-bounded droplets called liposomes that can form when lipid molecules are added to water - Form a unique internal chemistry - Are capable of simple reproduction and metabolism THE ORIGINS OF INFORMATION AND METABOLISM - The development of a system for the storage, replication, and translation of information for protein synthesis and the development of metabolic pathways that would capture and harness energy for metabolism. - All organisms contain deoxyribonucleic acid (DNA). - DNA = large, double stranded, helical molecule. - The information in DNA is copied onto molecules of a related substance, ribonucleic acid (RNA), which then directs the production of protein molecules. RIBOZYMES ARE BIOLOGICAL CATALYSTS THAT ARE NOT PROTEINS - Ribozymes are a group of RNA molecules that could themselves act as cat
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