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Lecture 2

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Western University
Biology 1001A
Tom Haffie

September 18/2011 Biology Chapter 2- Origins of Life (Lecture 2) 2.1-What is Life? • Seven Characteristics that all forms of Life Share o Display Order (arranged in highly ordered manner, cell being fundamental of life) o Harness and Utilize Energy (acquire energy from environment to maintain highly ordered state) o Reproduce o Respond to stimuli (make adjustments based on changes in environment) o Exhibit Homeostasis (regulate internal environment) o Growth and Development (increase in size/number of cells) o Evolve (evolution over course of time) • The Fundamental unit of Life is the Cell o All organisms are composed of one or more cells.  Unicellular Organism- one cell is a functionally independent organism  Multicellular Organism- plants and animals. Life activities divided among specialized cells. o The Cell is the smallest unit that has the properties of life  If the cell is broken open the property of life is lost (unable to grow, reproduce, respond to outside stimuli) o Cell arise only from the growth and division of pre-existing cells  DNA and RNA cannot orchestrate the formation of an entire cell, only division of cell can Q- WHY ARE VIRUSES NOT CONSIDERED A FORM OF LIFE? A- BECAUSE THEY LACK THE CELLULAR MACHINERY TO SYNTHESIZE THEIR OWN PROTEINS 2.2-The Chemical Origins of Life • The Solar System and Earth were formed about 4.6 billion years ago The Oparin-Haldane Hypothesis The Miller-Urey Experiment - Organic molecules that formed the - Demonstrated that abiotic synthesis of building blocks of life (amino acids) could biologically important molecules is possible have been formed given the conditions that prevailed on primitive Earth, including Abiotic- non living a reducing atmosphere that lacked oxygen. - Ultraviolet light provided the energy to accumulate simple building blocks of life • Primordial Atmosphere o Contained abundance of water vapour, large quantities of hydrogen sulphide (H 2), Carbon dioxide (CO 2, ammonia (NH ),3and methane (CH ) 4 • Protobionists: The First Cells o Protobiont- term given to group of abiotically produced organic molecules that are surrounded by a membrane or membrane-like structure. They allowed for an internal environment to develop that was different from the external environment Q- WHAT WAS THE SIGNIFIGANCE OF THE MILLER-UREY EXPERIMENT? A- DEMONSTRATED THAT ABIOTIC SYNTHESIS OF BIOLOGICALLY IMPORTANT MOLECULES IS POSSIBLE (ORGANIC MOLECULES COULD BE SYNTHESIZED SPONTANEOUSLY UNDER CONDITIONS SIMULATING PRIMORDIAL EARTH) 2.3- The Origins of the Information System • 1979, a group of RNA molecules that could themselves act as catalysts were discovered; called RIBOZYMES o Can catalyze reactions on the precursor RNA molecules that lead to their own synthesis, as well as on unrelated RNA molecules o Ribozyme function depends on how it is folded (like protein) o Advantage is that they are single stranded and can fold into very specific shapes • Living cells required the development of several critical components; energy-harnessing pathways, and a system based on nucleic acids that could store and pass on information required to make proteins • Because Ribozymes can store information and drive catalysts, it is thought that RNA was the first molecule from which both DNA and proteins developed • Proteins became dominant structural and functional macromolecule of cells due to greater diversity • DNA is more stable than RNA and evolved as a better repository of genetic information • Early metabolism was probably based on simple oxidation-reduction reactions (redox) Q- IN WHAT WAYS WAS DNA BETTER THAN RNA AS A MEANS OF STORING GENETIC INFORMATION? A- THREE MAJOR REASONS: 1. DUE TO DEOXYRIBOSE, DNA IS CHEMICALLY MORE STABLE 2. BY USE OF THYMINE OPPOSED TO URACIL, (IT IS THOUGHT THAT) ANY DAMAGED CYTOSINE CAN BE RECOGNISED AND REPAIRED 3. DNA IS DOUBLE STRANDED SUCH THAT MUTATIONS ON ONE STRAND CAN BE REPAIRED BY COMPLEMENTARY STRAND 2.4- Early Life • Earliest Evidence of Life o Stromatolites- type of layered rock that is formed when microorganisms bind particles of sediment together forming thin sheets  Stromatolites dated to 2.3 billion years ago represent the earliest fossil evidence of life • Extraterrestrial origin of life o Panspermia- the hypothesis that very simple forms of life are present in space and seeded Earth soon after it cooled o The Earth formed 4.6 billion years ago and first fossil evidence 3.6 billion years ago. Scientists argue that this window fo
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