Week 3 Course Notes: Chapters 4-6
Week 3 Course Notes: Chapters 4-6 Biol 2002
U of M
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This 6 page Class Notes was uploaded by Sydney Diekmann on Monday September 21, 2015. The Class Notes belongs to Biol 2002 at University of Minnesota taught by Dr. Susan Wick, Dr. David Matthes in Fall 2015. Since its upload, it has received 118 views. For similar materials see Foundations of Biology in Biology at University of Minnesota.
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Chapter 4 Nucleic Acids and the RNA World RNA world hypothesis chemical evolution led to the existence of a ribonucleic RNA molecule that could replicate itself I errors in replication gt genetic variation gt natural selection 41 What is a Nucleic Acid nucleic acid polymer made up of monomers called nucleotides I components of nucleotides 1 a phosphate group 2 a fivecarbon sugar 3 a nitrogencontaining base I nucleotides polymerize to form nucleic acids 1 phosphodiester linkage result of condensation reaction gt formation of bond between a hydroxyl on sugar component of one nucleotide and phosphate group of another nucleotide 2 when the nucleotides involved contain the sugar ribose RNA is produced 3 when the nucleotides involved contain sugar deoxyribose DNA is produced I DNA and RNA strands are directional due to sugarphosphate backbone of nucleic acid 0 the order of different nitrogenous bases in a nucleic acid forms the molecule s primary structure I polymerization reactions that join nucleotides into nucleic acids are catalyzed by enzymes 0 potential energy of nucleotides raised through addition of phosphate group gt becomes quotactivatedquot gt why linking 2 phosphates with covalent bonds generates strong repulsive forces 42 DNA Structure and Function DNA and RNA molecules have a sugarphosphate backbone phosphodiester linkages and a sequence of any 4 nitrogen bases that extend from it I DNA strands are antiparallel which when twisted together form a double helix structure 0 structure is stabilized by hydrophobic interactions and by hydrogen bonding between the base pairs AT and GC I DNA carries the information required for the organism s growth and reproduction o DNA s primary structure is template for synthesis of a complementary strand gt Le contains the information needed for a copy of itself to be made 1 heatingenzymecatalyzed reactions cause double helix to separate 2 free deoxyribosenucleotides form hydrogen bonds with complementary bases on the original strand of DNA ie the template strand gt formation of phosphodiester linkages to create new strand ie the complementary strand 3 complementary base pairing allows each strand of DNA double helix to be copied exactly gt 2 daughter strands I stability of DNA makes it a poor catalyst 0 therefore could not catalyze reactions that promote its own replication first life form did not consist of RNA 43 RNA Structure and Function I RNA differs from DNA structurally because it has 3 levels of structure 0 primary structure ribose sugarphosphate backbone formed by phosphodiester linkages and sequence of nitrogenous bases gt pyrimidine base thymine replaced by uracil o secondary structure WITHINSTRAND BASE PAIRING by hydrogen bonding between pyramidine and purine bases AU and GC gt stemandlook structure hairpin where fold occurs is unpaired bases then bases repair on same strand 0 tertiary structure arises when secondary structures fold into more complex shapes gt diversity in size shape and reactivity I the structure of RNA makes it versatile 0 RNA is the intermediate structurally and functionally between DNA and proteins I RNA contains bases and can therefore function as an information containing molecule 0 RNA can make copies of itself I RNA can function as a catalytic molecule for chemical reactions 0 ribozymes 44 The First LifeForm in order to make a copy of itself the first living molecule had to 1 provide a template that could be copied 2 catalyze polymerization reactions that would link monomers into a copy of that template I RNA is capable of both processes gt proposition of first lifeform o no selfreplicating RNA molecules have been discovered yet Chapter 5 Carbohydrates carbohydratesugar monomers called monosaccharides small polymers called oligosaccharides large polymers called polysaccharides 51 Sugars as Monomers sugars provide chemical energy in cells and provide some of the molecular building blocks required for the synthesis of larger more complex compounds I ribose sugar required for the formation of the nucleotides that make up nucleic acids A Monosaccharides simple sugars monomers of carbohydrates molecular formula C3H503 0 same molecular formula different structures gt carbonyl group with multiple hydroxyl groups provide sugars with multiple reactive and hydrophilic groups gt can participate in many chemical reactions 0 number of carbon atoms present varies gt trioses 3carbon sugar pentose 5carbon sugar hexose 6carbon sugar 0 simple changes in structure can affect the sugar s function BIG IDEA many monosaccharides exist because many aspects of the structure are variable B Structure of Polysaccharides complex carbohydrates gt chains of sugars of varying lengths o polymerization occurs when a condensation reaction occurs between hydroxyl groups gt covalent interactions glycosidic linkage gt hydrolysis separates these linkages o the location and geometry of glycosidic linkages can vary gt linkages form between hydroxyl groups and every monosaccharide contains 2 hydroxyls starch in plants monosaccharides stored for later use in this form glycogen in animals monosaccharides store for later use in this form cellulose structural polysaccharide in plants major component of the cell wall chitin structural polysaccharide in fungi and animals cell wall for fungi and exoskeletons for crustaceans and insects peptidoglycan structural support in bacterial cell walls C Function of Carbohydrates 0 provide structural support gt cellulose and chitin are structural compounds that form long strands of molecules that overlap to form tough structure of cell walls gt few organisms have the enzymes to break down hydrolysis cellulose and chitin due to absence of water in cellulose fibers 0 cell identity gt the variety in the components and structure of carbohydrates means that they can display information to other cells through their structure PWP gt glycoprotein protein that has 1 carbohydrates covalently bonded to it gt each cell in the body has glycoproteins on the plasma membrane that identify it as part of your body 0 immune cells distinguish body cells from foreign cells bacteria gt each different type of cell has a different glycoprotein on its surface 0 Le nerve cells have different glycoproteins on their plasma membrane than muscle cells 0 energy storage gt carbohydrates store sunlight chemical energy as chemical energy 0 photosynthesis is the process where kinetic energy from sunlight is stored in the bonds of carbohydrates gt enzymes break down hydrolysis polysaccharides to release glucose from glycogen and starch o glycogen and starch are forms of stored monosaccharides gt energy stored in glucose is used to make ATP 0 the energy released when sugars are processed is used to synthesize ATP from ADP BIG IDEA carbohydrates store chemical energy and ATP makes the energy useful to the cell through processes like polymerization Chapter 6 Lipids Membranes and the First Cells plasmacell membrane layer of molecules that surrounds the cell interior and separates it from the environment I serves as a barrier by keeping harmful compounds out and allowing needed compounds to enter I keeps chemicals enclosed gt reactants collide more frequently gt chemical reactions necessary for life to occur 61 Lipid Structure and Function lipid carboncontaining compounds that are found in organisms and are largely nonpolar and hydrophobic ie do not dissolve easily in water due to significant hydrocarbon component I fatty acids are lipids that are the building blocks to other lipids consisting of a hydrocarbon chain bonded to a carboxyl COOH group I bond saturation of fatty acids is determined by the hydrocarbon structure 0 saturated hydrocarbon chains that only have single bonds between carbons gt fatty acid had the max number of hydrogen atoms attached to its carbon frame 0 unsaturated hydrocarbon chains that have one or more double bonds between carbons gt fatty acid has a lesser number of hydrogen atoms attached to its carbon frame A Types of Lipids found in Cells 1 fats nonpolar molecules consisting of three fatty acids linked by an ester linkage to a threecarbon molecule glycerol 2 steroids lipids consisting of thick hydrophobic fourring structure 0 differ from one another by functional groups attached to rings 3 phospholipids consist of glycerol linked to phosphate group which is linked to a chargedpolar organic molecule and two hydrocarbon chains isoprenoids or fatty acids gt polar head that is hydrophilic and nonpolar tail that is hydrophobic B Structure of Membrane Lipids I membraneforming lipids have polarhydrophilic region not found in all lipids and non polarhydrophobic region found in all lipids 0 example phospholipids have a polar head and a nonpolar tail 0 amphipathic compounds 0 that contain both hydrophilic and hydrophobic compounds 62 Phospholipid Bilayers amphipathic lipids can be one of two structures I micelles droplets where hydrophilic heads interact with water form hydrogen bonds and hydrophobic tails interact with each other I lipid bilayer when two sheets of lipid molecules align o hydrophilic heads in each layer face surrounding solution 0 hydrophobic tails face one another inside the bilayer A Selective Permeability of Lipid Bilayers I selective permeability some substances cross a membrane more easily than others 0 small nonpolar molecules cross quickly 0 large polar molecules cross slowly or not at all gt more stable when dissolved in water than in the nonpolar interior of bilayer and membrane I bond saturation and hydrocarbon chain length affect membrane fluidity and permeability o unsaturated hydrocarbon tails gt spaces between tails gt weakened barrier gt more permeabilityfluidity o saturated hydrocarbon tails gt fewer spaces gt stronger barrier gt less permeabilityfluidity I cholesterol reduces membrane permeability o steroid rings in cholesterol are bulky so they fill gaps in the membrane I temperature affects permeability 0 higher temperatures gt molecules in bilayer move more quickly gt more permeable 0 lower temperatures gt molecules in bilayer move more slowly gt less permeable 63 Diffusion and Osmosis A Diffusion spontaneous movement of moleculesions that results from their kinetic energy I difference in solute concentrations creates concentration gradient 0 movement of molecules from areas of high concentration to areas of low concentration gt spontaneous results in an increase in entropy B Osmosis specific case of diffusion involved with the movement of water I occurs when solutions of different concentrations are separated by a selectively permeable membrane 0 only unbound water molecules can diffuse across membrane I can either swell or shrink membranebound vesicle 1 hypotonic solution inside membrane has lower concentration than exterior gt water leaves vesicle 2 hypertonic solution inside membrane has higher concentration than exterior gt water enters vesicle 3 isotonic solution inside membrane and solution outside membrane have equal concentrations gt no m movement of water
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