2 1 Atomic Structure is the Basis for Life s Chemistry 1 Matter composed of atoms Chapter 2 a Each atom consists of positive charged nucleus ade up of protons and neutrons b Surrounded by electrons bearing negative charges 2 Mass of proton neutron is one dalton 1 7x10 24 grams 3 Mass of electron 0 0005 Da 9x10 28 4 Element is pure substance that contains only one kind of atom a of protons in nucleus defines element 5 Most organisms composed of a Carbon b Hydrogen c Nitrogen d Oxygen e Phosphorus f Sulfur 6 Atomic number of protons 7 Mass number protons neutrons 8 Electron shells a First shell two electrons b Second and greater eight electrons 9 Molecules two or more atoms bonded together 2 2 Atoms interact and form molecules 10 Ionic bonds a Form when atoms gain or lose one or more electrons to achieve stability b Ion is electrically charged particle that forms when an atom gains or loses one or more electrons c i Cations positive charge ion ii Anions negative charged ion Ionic bonds form when ions with opp Charges attract result in stable molecules that are often referred to as salt i 11 Covalent bond Ionic attractions are weak salts dissolve in water 1 give molecules their 3 d geometry and shapes of molecules contribute to biological a Sharing one or more pairs of electrons Important aspects of covalent bonds b i Orientation 1 very strong therefore lots of energy to break them functions ii strength and stability iii multiple covalent bonds 1 single double triple bonds iv degree of sharing electrons 1 attractive force an atomic nucleus exerts on electrons in a covalent bond is electronegativity a electronegativity depends on how many protons molecule has v Polar covalent bond electrons drawn to one nucleus more than the other 1 Oxygen has slightly negative charge in H20 delta negative 12 Hydrogen bonds a May form between hydrogen and strongly electronegative atom b contributes two properties of water i Heat capacity 1 Raising them of liquid water takes a lot of heat 2 High heat of vaporization a lot of heat required to change water from liq To gas ii Cohesion 1 capacity of water to resist coming apart from one another when placed under tension 13 Polar molecules are hydrophilic water loving a in aqueous solutions these molecules become separated and surrounded by water molecules 14 Nonpolar molecules are hydrophobic water hating a weaker bonds and cause nonpolar substances to aggregate 15 Functional groups a Has specific chemical properties and when attached to larger molecule give those properties to larger molecules b One propery is polarity c Determine molecular shape and reactivity 16 Macromolecules large molecules formed by covalent linkages of smaller molecules a Formed by condensation rxns that link together monomers containing particular functional b Four kinds are characteristic of living things 1 formed from different combinations of 20 amino acids all of which share chemical 1 formed by linking together chemically similar sugar monomers monosaccharides to groups i Proteins similarities ii carbohydrates form polysaccharides iii nucleic acids iv lipids 1 formed from four kinds of nucleotide monomers linked together in long chains 1 noncovalent forces maintain the interactions between lipid monomers c With exception of lipids all are polymers constructed by covalent bonding of smaller molecules called monomers i polymers broken down by seiries of reactions involving water 1 condensation removal of water links monomers together 2 hydrolysis addition of water breaks polymer into monomers 2 3 Carbohydrates consist of sugar molecules 17 Carbohydrates general formula Cn H2O n 18 Carbohydrates have four major biochemical roles a They are a source of stored energy that can be released in a form usable by organisms b They are used to transport stored energy within complex organisms c They function as structural molecules that give many organisms their shapes d They serve as recognition or signaling molecuels tat can trigger specific biological responses 19 Monosaccharides are simple molecules with up to seven carbon atoms a Pentoses are five carbon sugars b Hexoses six carbon sugars all have formula C6H12O6 Include glucose fructose mannose and galactose i c Disaccharides oligosaccharides and polysaccharides are all constructed from monosaccharides that are covalently bonded by condensation reactions that form glycosidic linkages i a single glycosidic linkage between two monosaccharides forms a disaccharide ii polysaccharides contain long chains of monomers d Oligosaccharides contain several monosaccharides bound together by glycosidic linkages 20 Polysaccharides a Large polymers of monosaccharides connected by glycosidic linkages b Starches comprise a family of molecules that are all polysacharides of glucose i principal energy storage of plants c Glycogen is water insoluble highly branched polymer of glucose i major energy storage molecule in mammals d Cellulose is most abundant carbon containing biological compound on earth i polysaccharide of glucose but much more stable molecule than starch 2 4 Lipids Are Hydrophobic Molecules 21 Lipids are hydrocarbons and are insoluble in water because of nonpolar covalent bonds a Have several roles in living organisms i Store energy in C C and C H bonds ii Structural roles in cell membranes and on body surfaces iii Thermal insulation 22 Common units are triglycerides AKA simple lipids If solid at room temp around 20 degrees Celsius are called fats If liquid at room temp called oils a b c Contains three fatty acid molecules and one glycerol molecule i Glycerol is small molecule with three hydroxyl groups therefore an alcohol d Fatty acid consists of long nonplar hydrocarbon chain attached to a polar carboxyl group therefore a carboxylic acid i Saturated fatty acid 1 all bonds between carbon atoms in hydrocarbon chain are single 2 no double bonds 3 Molecules rigid and straight and are packed tightly ii Unsaturated fatty acid 1 Hydrocarbon chain contain one or more double bonds 2 Have kinks in the chain due to double bonds preventing molecules from being packed together tightly low melting points and are liquid at room temp iii Fatty acid has hydrophilic end and long hydrophobic tail 1 Two opposing chemical properties called amphipathic both polar and nonpolar ends e Phospholipids two fatty acids and a hydrophilic phosphate containing polr group attached to glycerol i Phosphate containing compound replaces one of the fatty acids giving