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The Chemical Building Blocks of Life Carbon Chapter 3 • Framework of biological molecules consists primarily of carbon bonded to – Carbon – O, N, S, P or H • Can form up to 4 covalent bonds • Hydrocarbons – molecule consisting only of carbon and hydrogen – Nonpolar – Functional groups add chemical properties 2 Isomers • Molecules with the same molecular or empirical formula – Structural isomers – Stereoisomers – differ in how groups attached • Enantiomers – mirror image molecules – chiral – D-sugars and L-amino acids 3 4 Macromolecules • 4 classes of large biological molecules – – – – Carbohydrates Nucleic acids Proteins Lipids • Polymers – Made of linked monomers • small, similar chemical subunits (building blocks) 5 6 Carbohydrates • Dehydration synthesis – Formation of large molecules by the removal of water – Monomers are joined to form polymers • Molecules with a 1:2:1 ratio of carbon, hydrogen, oxygen • Empirical formula (CH2O)n • Hydrolysis – Breakdown of large molecules by the addition of water – Polymers are broken down to monomers • C—H covalent bonds hold much energy – Carbohydrates are good energy storage molecules – Examples: glucose, starch, glycogen 7 8 Monosaccharides • Simplest carbohydrate • 6 carbon sugars play important roles – Glucose C6H12O6 – Fructose is a structural isomer of glucose – Galactose is a stereoisomer of glucose • Enzymes that act on different sugars can distinguish structural and stereoisomers of this basic six-carbon skeleton 9 10 Disaccharides • 2 monosaccharides linked together by dehydration synthesis • Examples: sucrose, lactose, maltose 11 12 Polysaccharides Starch • Long chains (polymers) of monosaccharides (monomers) • Energy storage – Plants use starch – Animals use glycogen • Structural support – Plants use cellulose – Arthropods and fungi use chitin Glycogen 13 Cellulose 14 Nucleic acids • Polymer – nucleic acids • Monomers – nucleotides – sugar + phosphate + nitrogenous base – Sugar is deoxyribose in DNA or ribose in RNA – Nitrogenous bases include • Purines: adenine and guanine • Pyrimidines: thymine, cytosine, uracil – Nucleotides connected by phosphodiester bonds 15 16 17 18 19 20 Deoxyribonucleic acid (DNA) • Encodes information for amino acid sequence of proteins – Sequence of bases • Double helix – 2 polynucleotide strands connected by hydrogen bonds – Base-pairing rules • A with T • G with C Ribonucleic acid (RNA) • RNA similar to DNA except – Contains ribose instead of deoxyribose – Contains uracil instead of thymine • Single polynucleotide strand • RNA uses information in DNA to specify sequence of amino acids in proteins 21 Other nucleotides 22 Proteins Protein functions include: 1. Enzyme catalysis 2. Defense 3. Transport 4. Support 5. Motion 6. Regulation 7. Storage • ATP - adenosine triphosphate – Primary energy currency of the cell • NAD+ and FAD+ – Electron carriers for many cellular reactions 23 24 • Proteins are polymers • Amino acids joined by dehydration synthesis – Composed of 1 or more long, unbranched chains – Each chain is a polypeptide – Peptide bond • Amino acids are monomers • Amino acid structure – Central carbon atom – Amino group – Carboxyl group – Single hydrogen – Variable R group 25 26 4 Levels of structure 4 Levels of structure • The shape of a protein determines its function 1. Primary structure – sequence of amino acids 2. Secondary structure – localized interaction of amino acids 3. Tertiary structure – folded 3-D shape od polypeptide chain – Stabilized by a number of forces 4. Quaternary structure – arrangement of individual chains (subunits) in a protein with 2 or more polypeptide chains – ! helix – " sheet 27 28 Additional structural characteristics • Motifs – Common elements of secondary structure seen in many polypeptides – Useful in determining the function of unknown proteins • Domains – Functional units within a larger structure – Most proteins made of multiple domains that perform different parts of the protein’s function 29 30 Chaperones • Once thought newly made proteins folded spontaneously • Chaperone proteins help protein fold correctly • Deficiencies in chaperone proteins implicated in certain diseases – Cystic fibrosis is a hereditary disorder • In some individuals, protein appears to have correct amino acid sequence but fails to fold 31 32 Denaturation Lipids • Protein loses structure and function • Due to environmental conditions • Loosely defined group of molecules with one main chemical characteristic – They are insoluble in water • High proportion of nonpolar C—H bonds causes the molecule to be hydrophobic • Fats, oils, waxes, cholesterol, steroid hormones, prostaglandins and even some vitamins – pH – Temperature – Ionic concentration of solution 33 34 Saturated fat Fats Unsaturated fat • Triglycerides – Composed of 1 glycerol and 3 fatty acids • Fatty acids – Need not be identical – Chain length varies – Saturated – no double bonds between carbon atoms • Higher melting point, animal origin – Unsaturated – 1 or more double bonds • Low melting point, plant origin – Trans fats produced industrially 35 36 Phospholipids • Composed of – Glycerol – 2 fatty acids – nonpolar “tails” – A phosphate group – polar “head” • Form all biological membranes 37 • Micelles – amphipathic lipid molecules orient with polar (hydrophilic) head toward water and nonpolar (hydrophobic) tails away from water 39 38 • Phospholipid bilayer – more complicated structure where 2 layers form – Hydrophilic heads point outward – Hydrophobic tails point inward toward each other 40