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Chapter 2

Chapter 2: Origins of Life; Textbook with diagrams

15 Pages

Course Code
BIOL 1000
Julie Clark

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Chapter 2: Origins of Life Ch. 2.1b The Fundamental Unit of Life is the Cell • Cell Theory: 1. All organisms are composed of one or more cells • Prokaryotes are composed of a single cell • In unicellular organisms, the one cell is functionally independent, capable of life activities. • In more complex cells, life activites are divided among specialized cells ○ Individual cells of multicellular organisms are potentially capable of surviving alone if placed in a chemical medium that can sustain them • Metabolic processes occur in cells 1. The cell is the smallest unit that has the properties of life • Opening cells destroys the property of life and all life activities cease to occur. 1. Cells arise only from the growth & division of pre- existing cells • Cells carry hereitable information: ○ DNA & RNA contain the info required to manufacture a vast array of biological molecules. • New cells can arise only from the division of pre-existing cells. Ch. 2.3a The Origin of the Information System • All organisms contain DNA, a large, double stranded, helical molecule that contains a unique alphabet that provides the instructions to assemble important cell components from simpler molecules • DNA functions similarly in all organisms: ○ Info in DNA is copied onto molecules of RNA, which then directs the production of protein molecules ○ Even simple cells contain thousands of proteins coded from a DNA sequence. • Enzymes are required to catalyze the replication of DNA, the transcription of DNA into RNA & finally the translation of RNA into a protein • Info is preserved from generation to generation by the ability of DNA to direct its own replication so offspring receive the same molecular instructions their parents have. Ch. 2.3d The Development of Energy Harnessing Reaction Pathways • Oxidation-reduction rxns were the first E releasing rxns of the primitive cells • Humans oxidize food molecules & use liberated E (electrons) to reduce other molecules (ex. Those needed to synthesize proteins) • Electrons removed in an oxidation rxn in a primitive cell would be transferred directly to the OA in a 1 step process. ○ Changed over time b/c it wastes too much E into a multi step process where E from oxidation is released slowly. • ATP links E releasing rxns to those requiring E ○ May have 1 entered early cells as one of the organic molecules absorbed from the primitive environment, initially hydrolyzed into ADP & Pi causing a release of E ○ E releasing during electron transfer was used to synthesize ATP from ADP & Pi. Ch. 2.4 Early Life Ch. 2.4a Earliest Evidence of Life • Stromalites are a type of layered rock that is formed when microorganisms bind particles of sediment together, forming thin sheets. • Modern day stromalites are formed by the action of a group of photosynthetic prokaryotes called cyano bacteria • Evidence of early life is given from carbon composition in rocks as these organisms would have the ability to take CO2 from the atmosphere & fix it by incorporating it into various forms (sugar, etc) • Panspermia is the hypothesis that very simple forms of life are present in space & seeded Earth soon after it cooled • Both Prokaryotic & eukaryotic cells share common features: ○ Plasma membrane: separates external environment from the cytoplasm consisting of the cytosol and organelles ○ Electron transport chains: used to link the oxidation of molecules to the synthesis of ATP. ○ Transcription translation machinery that relies on ribosomes for the synthesis of proteins from RNA ○ Both DNA is organized in chromosomes.  DNA of a prokaryote lacks a nucleus, and is localized into the nucleoid • Some early cells developed the capacity to carry out photosynthesis using water as an electron donor; the oxygen produced as a by-product accumulated, and the oxidizing character of Earth’s atmosphere increased. From this time on, organic molecules produced in the environment were quickly broken down by oxidation, and life could arise only from preexisting life, as in today’s world. ○ Photosynthesis that relies on the oxidation of water is called oxygenic photosynthesis ○ In aerobic respiration, E is extracted from food molecules, with O2 acting as the final electron acceptor. ○ Aerobic respiration allows organisms to extract a much greater amount of E from food then anerorbic respiration. Ch. 2.5 Eukaryotic Cells • Eukaryotic cells possess an endomembrane system (collection of interrelated membranous sacs that divide the organelle) that probably evolved from infolding of the plasma membrane. ○ Consists of the nuclear envelope, the ER, and the Golgi complex ○ Infolding of the plasma membrane is believed to be responsible for the evolution of organelles explained by pockets of the plasma membrane extending inward & surrounding the nuclear region to fuse around DNA and form the nuclear envelope & nucleus  Remaining membranes formed vesicles giving rise to the ER & golgi complex • Membranes of the endomembrane system are connected by vesicles, which are small membrane bound compartments that transfer substances b/w parts of the system • Cytoplasm: cytosol & extra nuclear organelles • Lumen: interior of organelle • Cytosol: cell contents excluding organelles • The ER occurs in 2 forms: ○ Smooth: synthesizes lipids & breaks down toxic substances ○ Rough: makes proteins that become part of cell membranes or are released to the cell surface within vesicles that pinch off from the ER and join the golgi complex. ○ Proteins made by freely suspended ribosomes in the cytosol pass through the nuclear pores to enter the nucleus or become parts of other structures. • The Golgi complex chemically modifies proteins made in the rough ER and sorts finished proteins to be secreted from the cell or embedded in the plasma membrane ○ Proteins secreted from the cell are transported to the plasma membrane by secretory vesicles that release their contents to the exterior via exocytosis. Cells may also enter the cell via endocytosis. • Lysosomes budding from the golgi membrane contain hydrolytic enzymes that digest damaged organelles or contents of endocytic vesicles that fuse with them. • The E transducing organelles-chloroplasts & mitochondria- are thought to have been derived from free-living prokaryotic cells • Eukaryotic Nucleus: ○ Contains DNA & associated proteins, machi
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