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Origins of Life Objectives • The primitive earth • The primitive atmosphere • Theories on the origin of life • Matter & Energy • Cell surface-to-volume ratio Let’s start at the beginning… • Scientists believe the universe started with The Big Bang • Evidence for this comes from the fact that we know the universe is always expanding • According to second law of thermodynamics, the universe is increasing in entropy (disorder) as time goes on • What we find is that life is becoming more and more complex (orderly). • We do this at the expense of our universe and ‘pay for order’ in the form of energy Two things keep us from being killed by the sun’s radiation 1. The magnetosphere formed by the movement of the iron core 2. The atmosphere The Primitive Atmosphere • The primitive atmosphere was made up of hydrogen, ammonia and methane • Nitrogen, carbon dioxide, sulfur dioxide, and water vapor emitted from volcanoes replaced the remaining primitive gases • The earth is 4.6 billion years old • The earth was too hostile for life until about 3.9 bya • First fossils date back to 3.5 bya Origin of life What’s wrong with this graph? Origin of Life Overview • Primitive Earth provided inorganic precursors from which organic molecules could have been synthesized due to the presence of available free energy and the absence of a significant quantity of oxygen • In turn, these molecules served as monomers or building blocks for the formation of more complex molecules, including amino acids and nucleotides. • The joining of these monomers produced polymers with the ability to replicate, store and transfer information. • These complex reaction sets could have occurred in solution (organic soup model) or as reactions on solid reactive surfaces. • The RNA World hypothesis proposes that RNA could have been the earliest genetic material Evidence for the origin of life • Geological • Fossil record • Chemical • Miller-Urey experiment • Molecular • Shared genes • Common characteristics for life Geologic Time Scale • No oxygen oxygen • No life life • Single-celled multi-celled • Prokaryote eukaryote (no nucleus nucleus) • Dating fossils • Not ONE thing out of order Miller-Urey Experiment • Done in the 1950’s • Abiogenesis: the creation of life (organic matter) from non-life (inorganic matter) • When they simulated the early atmosphere they collected more complex molecules and amino acids that had been synthesized over time • This was a sterile environment with NO gaseous oxygen Expanding upon the Miller-Urey • His experiment is still going • Now can find up to 25 different amino acids • These amino acids are considered “old” in terms of ancient genes • Other scientists who have repeated his experiment have found the formation of nucleic acids (DNA & RNA) Molecular Evidence • We all came from a common ancestor • ALL LIFE • Uses DNA and/or RNA to transmit information between generations • Uses proteins to carry our metabolic functions • Uses ATP for energy • Has a cellular membranes made up of a phospholipid bilayer • Undergo cell division • You share 50% of your DNA with a banana • If it were by chance, you would share 25% of your DNA (because there are four letters in the genetic code) Energy + Matter = Life Need energy and matter for: • Growth • Homeostasis • Reproduction • In accordance with the laws of thermodynamics, to offset entropy, energy input must exceed energy lost from and used by an organism to maintain order • All of this takes a massive coordination between obtaining energy and utilizing macromolecules Energy • Getting energy • Autotrophs: photosynthesis to capture free energy from sun and turn it into sugars and CO2 • Heterotrophs: eat plants or animals & use the carbon molecules they made already • Using energy • Cellular respiration (with oxygen) and fermentation (without oxygen) harvest free energy from sugars to produce free energy carriers, including ATP. • Storing energy • fats Matter • Cells & organisms must exchange matter with the environment in order to make complex molecules WATER CARBON NITROGEN PHOSPOROUS Overview • There are four macromolecules The Big Picture • Cells & organisms must exchange matter with the environment and all life uses the same elements to build their macromolecules WATER CARBON Proteins NITROGEN Nucleic Acids PHOSPOROUS Carbohydrates Lipids Cell Surface Area-to-Volume Ratio • A cell is CONSTANTLY interacting with their environment • Cell MUST be able to bring stuff into the cell (endocytosis) & get waste out of the cell (exocytosis) • As a cell grows, it’s volume increases faster than it’s surface area (decreasing SA-to-V ratio) • If cell gets too big, the middle of the cell becomes too disconnected from the outside world Video • https://www.youtube.com/watch?v=3yOUgTaKDkM