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Lecture 3

Biology 1001A Lecture 3.pdf

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Western University
Biology 1001A
Beth Mac Dougall- Shackleton

Biology 1001A | 2012 LECTURE NOTES Lecture 3 The Origins of Life –––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– Viruses Are Not Alive - viruses have to rely on other forms of life - but humans also rely heavily on organisms to survive So, What is life? - Seven Characteristics of Life a. display order b. harness and utilize energy c. reproduce d. respond to stimuli e. exhibit homeostasis f. growth and development g. evolve - you can’t simply say that something is not life because it doesn’t have DNA What do we know about life? - the earth has been around for 4.6 billion years - we have geological evidence of life dating to 3.5 billion years ago called stromatolites - these are produced by cyanobacteria - these are believed to have been produced by microbial activity - cyanobacteria are fairly complex organism capable of photosynthesis like modern plants - it is believe that some form of life predated the cyanobacteria, therefore the start of life might have been around 4.0 billion years ago - it seems that relative to the age of earth, life developed quite fast LUCA (last universal common ancestor) - all cellular life fits on the tree of life - it is believed that bacteria, archaea and eukaryotes have a single common ancestor called LUCA because similarities in biochemical characteristics such as: ▯ 1. cells are made of lipids ▯ 2. genetic systems based on DNA ▯ 3. DNA to RNA to protein transfer of information ▯ 4. common system of protein assembly ▯ 5. everything uses ATP ▯ 6. glucose & glycolysis - this does not mean that there was only one form of primitive life, it means that this was the last one which was common to all current forms of life - there were many initial forms of life, but the one that had the biochemistry similar to modern forms are Biology 1001A | 2012 Prokaryotes don’t exist - no single group of organisms that can be defined as prokaryotes - the idea that prokaryotes came before eukaryotes is not substantiated by any proof - bacteria and archaea were often put together and called prokaryotes but they are very unrelated as they share no ancestors after LUCA - archaea are actually more closely related to eukaryotes than they are to bacteria - the lack of nuclear envelopes in bacteria and archaea developed independently of each other - “pro” suggests that prokaryotes came before the eukaryotes, and that eukaryotes are therefore an advancement of prokaryotes, this is wrong - there is no evidence to suggest that prokaryotes came before eukaryotes - the idea that eukaryotes are always more advanced organisms is also incorrect - evolution does not have to go from simple to complex organisms - it is possible that LUCA was a proto-eukaryote and that it had a nuclear envelope and metabolic processes that are not present in bacteria or archaea - bacteria and archaea got rid of many things due to reductive evolution - reductive evolution is the removal of unnecessary things the streamlining of systems - this makes the organism more energy efficient, faster at reproduction - but why would the bacteria and archaea get rid of the eukaryotic stuff? - to save energy - faster rate of reproduction - extremophiles - can grow in hot springs and other extreme environments where eukaryotes can’t live Stages of Prebiotic Evolution - so what do you need? - abiotic synthesis – creation of biological molecules without living organisms - heritable information - cells - metabolism - three stages of prebiotic evolution i) Geophysical stage –> what was the composition of the Earth and the atmosphere? ii)Chemical Stage –> how could the building blocks of life be synthesized abiotically? iii)Biological Stage -> how did the building blocks organize into living cells? - this was investigated by the Miller-Urey Experiment - the process for making the necessary molecules abiotically is reasonably well understood, but how this was able to be formed into living organisms capable of reproducing is not well understood - Australopithecus afarensis - our ancestors looked very different from us 4 million years ago - explaining evolution of life is easy, explaining the start of life is difficult Biology 1001A | 2012 ii) Chemical Stage - Miller-Urey experiment proved that molecules needed for biological systems can be synthesized abiotically - unanswered questions - although Miller-Urey produced monomers, it d
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