BIO358 Lecture 1 - Origins of Life PDF

Defining Life and the Chemistry of Life Chapter 3 Carlo Bastianutto, PhD Image from https://opherworld.files.wordpress.com/2015/03/evolution6.jp g  Overview What is life Chemical origins of life Ma...

Defining Life and the Chemistry of Life Chapter 3 Carlo Bastianutto, PhD Image from https://opherworld.files.wordpress.com/2015/03/evolution6.jp g  Overview What is life Chemical origins of life Macromolecules of life Earliest life forms Eukaryotic cells and Multicellularity What is Life ?  Properties of Life All life is composed of cells Common Characteristics: Display same hierarchy Harness and utilize energy (metabolism) Sense and respond to stimuli Regulate through homeostasis All have genetic material which allow them to grow, reproduce and evolve independently  Properties of Life hierar chy Cell :basic unit of life geneti c Living need for mater Organisms energ ial y growth (DNA) Mutation/ interdepend metabolis Evolution ence m reproduc tion homeost asis responsive irritability ness  Why Viruses are not living organisms Contain nucleic acids, but lack their own cellular machinery Lack metabolism Completely dependent on living cells for reproduction Do not comply with the seven characteristics of life (respire, grow, excrete, reproduce, metabolize, move, and respond)  How did life originate? 4.6 billion years ago now Origins of Life - Prokaryotes At one point, no cells, hence no life existed Earth formed 4.6 billion years ago Life likely started around 3.8-4 billion years ago First clear fossil evidence of prokaryotic cells occurs 3.6 billion years ago  Origins of Life - Eukaryotes Eukaryotes emerged 2 billion years ago Animals 525 million years ago Humans have existed for only 150,000 years Origins of Life - Prokaryotes First fossil evidence of prokaryotes 3.6 billion years stromatolites cyanobacteria  Earth – A Habitable Zone Earth is in the habitable zone: distance from the sun allowed for liquid water to exist  Evolution of Life Evolution of life would have involved different steps Formation of biomolecules Assembly of biomolecules into cell like structure Acquisition of genetic capability by one of the biomolecules  Biologically Important Molecules Life is based on major macromolecules (biomolecules) Nucleic acids Proteins Lipids Carbohydrates http://scienceforkids.kidipede.com/chemistry/organic/ Can develop from simpler molecules protein.htm How did biomolecules originate? Three main hypotheses: Reducing atmosphere Deep-Sea Vents Extraterrestrial Origin  Reducing Atmosphere and molecules Primordial atmosphere (4 billion years ago) contained: Water vapor (H2O) Hydrogen (H2) Ammonia (NH3) Methane(CH4) No O2  Primordial Earth – Reducing Atmosphere In the 1920’s, Scientists - Oparin and Haldane proposed the primordial earth had a “reducing atmosphere” Early molecules (H2, CH4, NH3) contain abundance of electrons Very reactive molecules Can participate in reactions yielding larger more complex molecules Current Atmosphere - Oxidizing Today’s atmosphere – oxidizing High levels of oxygen are present which oxidizes molecules  UV light and Lightning Energy The lack of ozone in the atmosphere would allow energetic UV light to reach the lower atmosphere Lightning also abundant Energy sources for driving the formation of biological molecules  Miller – Urey Experiment Stanley Miller (1953), a graduate student, simulated the early reducing atmosphere by mixing H2, CH4, NH3, H2O in a closed chamber Energy was provided by sparking electrodes  Miller - Urey Experiment After one week many organic molecules were detected: Urea Amino acids Urea Lactic acid Formic acid Acetic acid Lactic acid Common in living organisms  More complex molecules If hydrogen cyanide (HCN) and formaldehyde were added to experiment Purines and pyrimidines formed, the components of nucleic acids Also, amino acids and fatty acids Sugars included: glyceraldehyde, ribose, glucose and fructose All molecules critical for life  Role of Deep Sea Vents Deep Sea (hydrothermal) vents also provide heat and reduced molecules including: methane, ammonia hydrogen sulfide https://images.app.goo.gl/ mwX1RmcE3HyATux18  Extraterrestrial origins Key organic molecules may have come from space via carbonaceous chondrite meteorites Rich in organic molecules including: amino acids (glycine, glutamic acid and alanine) Purines, pyrimidines  From monomers to polymers Polymers (macromolecules; e.g.: proteins, DNA) formed by monomers (simple molecules; e.g. amino acids) bonded together Solid surfaces, like clays, could have enabled a polymerization friendly environment (clay hypothesis)  Key attribute of life How did we go from Biomolecules to living organisms? Key attributes of life: Membrane to define compartment System to store genetic information and translate it into proteins Pathways to acquire and use energy  Lipid spheres (liposomes) Lipid spheres = compartments May have led to the development of early cells – a closed space allowing reactions to proceed Probiont = abiotically produced organic molecules surrounded by a membrane  Probionts Probionts can spontaneously form similar to liposomes (lipid vesicles) – bilayer structures Selectively permeable – only specific molecules can move in and out Clay also accelerates the formation of lipid vesicles  The central dogma Life now: Proteins “execute” the information through enzymatic activity Information is Information Information stored in DNA in DNA is copied in RNA guides the into RNA synthesis of proteins  The central dogma Life at the beginning? (RNA world): Information is stored and executed by RNA  RNA World – Information and Catalysis Ribonucleic acid (RNA) may have been the first genetic and enzyme molecule RNA can act as catalysts (i.e., ribozymes) which catalyze reactions Folding of RNA molecules into specific shapes can: impart function http://en.wikipedia.org/wiki/Ribozyme carrier of information RNA later replaced by DNA & Proteins Specialized molecules for information storage and catalytic functions developed Some RNA molecules may have been able to direct the synthesis of small proteins More variability in proteins (20aa vs 4 nucleotides) => more biological catalysts DNA then emerged and is chemically more stable than RNA  Simple Oxidation Reduction Reactions Simple step reactions occurred first, leading to more efficient multi-step reactions ATP became established as the coupling agent that links energy- releasing and energy-requiring reactions http://www2.estrellamountain.edu/faculty/farabee/BIOBK/BioBookATP.html  Earliest Forms of Life Stromatolites are the earliest fossilized evidence of life deposits formed by the action of photosynthetic bacteria (cyanobacteria) Used oxygenic photosynthesis – using sunlight to oxidize water and release oxygen.  Common Ancestor Present day organisms categorized in one of three domains: Archaea Prokaryotes Bacteria Eukaryotes All arose from a common ancestor LUCA: Last Universal Common Ancestor Common Ancestor  Eukaryotic Cells and Multicellularity Eukaryotes arose approximately 2.5 billion years ago Characteristics: 1. Separation of DNA and cytoplasm by a nuclear envelope 2. Membrane-bound compartments (organelles) with specialized functions in the cytoplasm  Eukaryotic Cells and Multicellularity Other organelles include: Mitochondria Chloroplasts Endoplasmic reticulum Golgi complex How did they originate? http://pencestudio.com/portfolio/animal-cell /  Endosymbiotic Theory Chloroplasts and mitochondria descended from free-living prokaryotic cells Mitochondria from aerobic bacteria Chloroplasts from photosynthetic cyanobacteria These cells were engulfed by larger prokaryotic cells forming an endosymbiotic relationship  Endosymbiotic Theory Chloroplasts and mitochondria have prokaryotic characteristics: Double membrane Independent reproduction Genetic information Both have circular DNA Mitochondrial DNA: 39 genes Chloroplast DNA: 100 genes Chloroplast DNA similar to cyanobacteria’s Ribosome type (70S) Endosymbiosis and Horizontal Gene Transfer Some proto-endosymbiotic genes would be redundant and gradually lost. Other genes were relocated to the nucleus Horizontal gene transfer  Why Eukaryotes? More energy efficient Specialized mitochondria enable greater energy production by the cells Cells could become more complex and support a greater volume and larger genome Allows for evolution of specialization and multicellularity  Summary Properties of Living Organisms How life may have originated on earth Theories explaining the formation of the first biomolecules and living cell (LUCA) Acquisition of basic life properties (energy, genetic material) RNA as the first genetic and enzymatic molecules From Prokaryotes to Eukaryotes Endosymbiosis Advantages of Eukaryotes