BES 108D Lecture 2: Organisms in Their Environment PDF

1 BES 108D Lecture 2 10th Jan 2025 Organisms in their environment By Dr. Benazir Alam ([email protected]) Copyright © 2025 Pearson Canada, Inc. 25 - 1  2 Topic 1: Prokaryotes: Bacte...

1 BES 108D Lecture 2 10th Jan 2025 Organisms in their environment By Dr. Benazir Alam ([email protected]) Copyright © 2025 Pearson Canada, Inc. 25 - 1  2 Topic 1: Prokaryotes: Bacteria and Archaea Chapter 25: The History of Life on Earth Copyright © 2025 Pearson Canada, Inc. 25 - 2  Conditions on Early Earth Made the Origin of Life Possible Chemical and physical processes on early Earth may have produced very simple cells through a sequence of stages: 1. Abiotic synthesis of small organic molecules such as amino acids and nitrogenous bases 2. Joining of these small molecules into macromolecules such as proteins and nucleic acids 3. Packaging of molecules into protocells droplets with membranes that maintained an internal chemistry different from that of their surroundings 4. Origin of self-replicating molecules that eventually made inheritance possible Copyright © 2025 Pearson Canada, Inc. 25 - 3 Synthesis of Organic Compounds on Early Earth (1 of 4) About 4.6 billion years ago, the solar system formed from a rotating disk of gas, rocks and dust. As particles collided and stuck together, they formed larger bodies, including planets such as earth. For its first few hundred million years, Bombardment of Earth by asteroids or commets that are composed up to dust, rocks and ice likely produced so much heat that all of the available water was vaporized and that prevented seas from forming before 4.2 to 3.9 billion years ago This massive bombardment ended 4 billion years ago, setting the stage for the origin of life. Copyright © 2025 Pearson Canada, Inc. 25 - 4 Synthesis of Organic Compounds on Early Earth (2 of 4) Earth’s early or the first atmosphere had little oxygen and likely contained – water vapour – chemicals released by volcanic eruptions, including nitrogen, nitrogen oxides, carbon dioxide, methane, ammonia, hydrogen, hydrogen sulfide – As Earth cooled, the water vapour condensed into oceans, and much of the hydrogen escaped into space likely due to its low molecular weight. High temperature of the earth at that time could have provided hydrogen molecules with sufficient energy to overcome Earth’s gravity. Some hydrogen may have reacted with oxygen to form water, which eventually condensed into oceans, further reducing the amount of hydrogen in the atmosphere. Copyright © 2025 Pearson Canada, Inc. 25 - 5 Synthesis of Organic Compounds on Early Earth (3 of 4) In the 1920s, A.I. Oparin and J.B.S. Haldane independently hypothesized that the early atmosphere was a reducing environment (electron gaining common in anaerobic conditions, such as in certain wetlands, deep-sea hydrothermal vents) They hypothesized that organic compounds could have formed from simpler molecules using the energy from lightning and intense UV radiation. Haldane suggested that the early oceans were a solution of organic molecules, a “primitive soup” from which life arose. In 1953, Stanley Miller and Harold Urey conducted lab experiments showing that the abiotic synthesis of organic molecules in a reducing atmosphere is possible Copyright © 2025 Pearson Canada, Inc. 25 - 6 Synthesis of Organic Compounds on Early Earth (4 of 4) The first organic compounds may have been synthesized near volcanoes or deep-sea vents with reducing environment Miller-Urey–type experiments demonstrate that organic molecules could have formed with various possible atmospheres Copyright © 2025 Pearson Canada, Inc. 25 - 7 Amino Acid Synthesis in a Simulated Volcanic Eruption Comparison of Miller and Urey’s 1953 experiment and 2008 reanalysis Copyright © 2025 Pearson Canada, Inc. 25 - 8 Organic Compounds May Have Been Produced Near Deep-Sea Vents qSome deep sea alkaline vents release water that has high pH (9-11) and warm 40-90º C qThis could have provided an environment suitable for the abiotic synthesis of organic molecules, and the first cells qEarly oceans were acidic, and so a pH gradient would have formed between the interior of the vents and the surrounding ocean water. qEnergy for the synthesis of organic compounds could have been harnessed from this pH gradient. Copyright © 2025 Pearson Canada, Inc. 25 - 9 Abiotic Synthesis of Macromolecules: Where did amino acids and organic molecules came from? Amino acids have also been found in meteorites Meteorite also contained other key organic molecules, including lipids, simple sugars, and nitrogenous bases such as uracil. RNA purine (adenine and guanine) and pyrimidine (cytosine and uracil) monomers could also be produced spontaneously from simple molecules Scientists have produced polymers of these molecules simply by dripping solutions of amino acids or RNA nucleotides onto hot sand (can provide heat), clay or rock without the help of enzymes or ribosomes The minerals in clay or rock can provide catalytic surface to facilitate the polymerization of these small molecules into larger chains, such as proteins or RNA. Copyright © 2025 Pearson Canada, Inc. 25 - 10  Protocells A protocell is a theoretical model of an early form of life that resembles a cell but lacks the complex structures and functions of modern cells. Protocells are often considered as a step in the transition from non-living chemical systems to living organisms. Replication and metabolism are key properties of life and may have appeared together in a protocell Protocells may have been fluid-filled vesicles with a membrane-like structure In water, lipids and other organic molecules can spontaneously form vesicles with a lipid bilayer Adding clay can increase the rate of vesicle formation Vesicles exhibit simple reproduction and metabolism and maintain an internal chemical environment Copyright © 2025 Pearson Canada, Inc. 25 - 11  12 Copyright © 2025 Pearson Canada, Inc. 25 - 12  Role of Montmorillonite clay in protocell formation Montmorillonite clay (composed primarily of silicate layers with aluminum and magnesium), common in early earth is produced by weathering of volcanic ash It provides surfaces on which organic molecules become concentrated, increasing the likelihood that the molecules will react with each other and form vesicles Copyright © 2025 Pearson Canada, Inc. 25 - 13 Self-Replicating RNA (1 of 2) The first genetic material was probably RNA, not DNA RNA plays a central role in protein synthesis, but it can also function as an enzyme-like catalyst RNA molecules called ribozymes catalyze many different reactions – For example, ribozymes can make complementary copies of short stretches of RNA given they are supplied with nucleotide building blocks Copyright © 2025 Pearson Canada, Inc. 25 - 14  Self-Replicating RNA (2 of 2) Natural selection on the molecular level might have produced ribozymes capable of self-replication in the laboratory. RNA molecules that were more stable or replicated more quickly would have dominated. Early genetic material might have formed an “RNA world” Small RNA molecules were able to replicate and store genetic information about the vesicles that carried them. Vesicles with RNA capable of replication would have been protocells although the first such protocells likely carried limited amounts of genetic information, specifying only a few properties. RNA could have provided the template for DNA, a double stranded genetically more stable material that could also be replicated more accurately Copyright © 2025 Pearson Canada, Inc. 25 - 15  16 Transition from RNA to DNA Accurate replication was advantageous as genomes grew larger through gene duplication and other processes and as more properties of the protocells became coded in genetic information. Once DNA appeared, the stage was set for the blossoming of new forms of life—a change we see documented in the fossil record Copyright © 2025 Pearson Canada, Inc. 25 - 16 The Fossil Record Documents the History of Life The fossil record reveals changes in the history of life on Earth Sedimentary rocks are deposited into layers called strata and are the richest source of fossils Copyright © 2025 Pearson Canada, Inc. 25 - 17 The Fossil Record (2 of 3) Keep in mind that a fossil is an incomplete chronicle of evolution. Many of Earth’s organisms did not die in the right place and time to be preserved as fossils. Of the fossils that were formed, many were destroyed by later geologic processes, and only a fraction of the others have been discovered. Few individuals have fossilized, and even fewer have been discovered The study of fossils has helped geologists establish a geologic record. The fossil record is biased in favour of species that – Existed for a long time – Were abundant and widespread – Had hard parts Copyright © 2025 Pearson Canada, Inc. 25 - 18  19 The Geologic Record Copyright © 2025 Pearson Canada, Inc. 25 - 19  How Rocks and Fossils Are Dated Sedimentary strata reveal relative ages of fossils, i.e. the sequence in which the fossils were laid down Absolute ages of fossils can be determined by radiometric dating – A radioactive “parent” isotope decays to a “daughter” isotope at a characteristic rate – Each isotope has known half-life, the time required for half of the parent isotope to decay which is not affected by temperature, pressure, or other environmental variables – Carbon-14 has a half-life of 5730 years. This means that after 5730 years, half of the original amount of Carbon-14 in a sample will have decayed. Uranium-238 decays has a half-life of 4.5 billion years. Copyright © 2025 Pearson Canada, Inc. 25 - 20 Radiometric Dating (2 of 2) A living organism contains the most common carbon isotope, carbon- 12, as well as a radioactive isotope, carbon-14. When the organism dies, it stops accumulating carbon-14, and the amount of carbon-12 in its tissues does not change over time. However, the carbon-14 that it contains at the time of death slowly decays into another element, nitrogen-14. By measuring the ratio of carbon-14 to carbon-12 in a fossil, we can determine the fossil’s age. Radiocarbon dating can be used to date fossils up to 75,000 years old To date older fossils, ages of sediments in sedimentary rocks are considered. If two volcanic layers surrounding fossils are found to be 525 million and 535 million years old, for example, then the fossils are roughly 530 million years old. Copyright © 2025 Pearson Canada, Inc. 25 - 21  Oxygen Revolution The initial rise in O2 was likely caused by oxygenic photosynthetic prokaryotes Later increases in atmospheric O2 might have been caused by the evolution of eukaryotic cells containing chloroplasts This “oxygen revolution” from 2.7 to 2.4 billion years ago caused extinction of many anaerobic prokaryotic groups Some groups survived and adapted using cellular respiration to harvest energy Copyright © 2025 Pearson Canada, Inc. 25 - 22