Chapter 6 Study Guide - Study Guide 6 UNIT I: - The Atoms...

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UNIT I: - The Atoms & Molecules of Ancient Earth (Basic Chemistry) - Thermodynamics and Chemical Energy - The Origin of Life’s Energy-Rich Molecules, Redox Reactions and Carbon; Functional Groups - The Properties of Water; Water Chemistry - Organic & Macromolecules; Polymerization, Chemical Evolution; Catalysis & the First Macromolecules - Lipids, Semi-Permeable Membranes and the First Cells A. Lipids: fats , phospholipids , steroids ; these are generally hydrophobic . 31232) fatty acids are long hydrocarbon chains with a single carboxyl (acidic) group at one end (see Figs. 6.2, 6.3 ). The hydrocarbon chain may be saturated or unsaturated . Unsaturated fatty acids have one or more double bonds between carbons. Animals can make saturated and mono-unsaturated, but not polyunsaturated fatty acids; we need both kinds. 2) Structure of fat: note the ester linkage between glycerol and 3 fatty acids ( Figs. 6.3b ). 3) phospholipids: two fatty acids and a phosphate-containing group ester-linked to the glycerol ( Fig. 6.4b ). Phospholipids have a hydrophobic fatty acid and a polar phosphate region; they are “ amphipathic ” and well- suited to form cellular membranes (shown at right, and see Figs. 6.5, 6.7 ). 4) steroids (e.g., cholesterol, Fig. 6.4a ): Cholesterol is an important component of cell membranes, and is a precursor to steroid (sex and adrenal) hormones. Cholesterol is also amphipathic. B. Membranes and the first cells While cells now have phospholipid bilayer membranes, the first semi-permeable barriers surrounding cells may have been made of other lipids or even proteins. Experiments have been dome to create artificial vesicles with such molecules ( Fig. 6.7a ), and the vesicles have been shown to be semi-permeable. Thus, the phospholipid bilayer membrane may have been a later evolutionary development, much as DNA is thought to have evolved after RNA as the informational molecule. 30928) The phospholipid bilayer structure of membranes was known since the early 1900s, when size and amount of phospholipids was correlated with the surface area of mammalian red blood cells: there are enough phospholipids per erythrocyte to wrap around each cell twice. The amphipathic nature of phospholipids (a hydrophobic and a hydrophilic part) suggested the bilayer structure ( Figs. 6.4, 6.5 ). When pure phospholipids are mixed with water, they can spontaneously (i.e., in an exergonic event) form phospholipid bilayer vesicles called
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Chapter 6 Study Guide - Study Guide 6 UNIT I: - The Atoms...

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