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Chapter 2- Origins of Life.docx

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York University
BIOL 1000
Paula Wilson

Notes on chapter2 (2.1b, 2.3a, 2.3d, 2.4, 2.5) 2.1 The Fundamental Unit of Life is the Cell  All organisms are composed of one or more cells  All cells come from preexisting cells  The cell is the smallest unit of life 2.3a The Origin of the Information System  All organisms contain deoxyribonucleic acid (DNA). DNA is a large , double-stranded, helical molecule that contain instructions for assembling many important components  DNA function similarly in all organisms – the Information in DNA is copied onto molecules of a related substance, ribonucleic acid (RNA) , which then directs the production of protein molecule  Enzymes are required to catalyze the replication of DNA, the transcription of DNA into RNA, and, subsequently, the translation of the RNA into protein. 2.3d The Development of Energy-Harnessing Reaction Pathways  Oxidation-reduction reaction were probably among the first energy-releasing reaction of the primitive cells  ATP may first have entered early cells as one of many organic molecules absorbed from the primitive environment 2.4a Earliest Evidence of Life  Stromatolites - are a type of layered rock that is forming when microorganisms bind particles of sediments together, forming thing sheets. 2.4b Could Life Have Come to Earth from Space  Life on earth developed very quickly after the earth was formed  The earth was formed 4.6 billion years ago, and we have clear fossil evidence of life dated to about 3.5 billion years ago and chemical evidence about 3.9 billion years ago  Extremophile can thrive under any harsh conditions 2.4c Prokaryotes Have Properties Common to All Cells  Prokaryotes – lack a nucleus  The cytoplasm consists of the cytosol, which is mostly water, salts and various organic molecules  The DNA of both prokaryotic and eukaryotic cells is organized into chromosomes. The structure of the chromosome is distinctly different between prokaryotes and eukaryotes.  DNA of a prokaryote is found localized in a central region of the cell called a nucleoid 2.4d Prokaryotes Display Remarkable Diversity  Prokaryotes have much less internal membrane organization  Prokaryotes display remarkable metabolic flexibility, being able to use a variety of substances as energy and carbon sources and to synthesize almost all of their required organic 2.24e Oxygenic Photosynthesis and the Rise of Atmospheric Oxygen  Geologic evidence indicates that the earliest prokaryotic cells relic on anaerobic metabolism as the atmosphere of the earth lacked molecular oxygen  However, starting about 3 billion years ago a group of prokaryotes called cyanobacteria appeared  A consequence of oxidizing water was that besides releasing electrons and protons, the “splitting of water” resulted in the formation of O2 , which was released and over millions of years slowly accumulated in the atmosphere  The development of oxygenic photosynthesis was also a critical even in the evaluation and diversification of life on earth because the rise in atmospheric O2 led quite rapidly to the evolution of prokaryotic cells, which are able to undergo aerobic respira
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