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• Chapter 4~ Carbon & The Molecular Diversity of Life • Chapter 5~ The Structure & Function of Macromolecules Organic chemistry • Carbon – tetravalence – Tetrahedron – shape determine function Hydrocarbons • • • • Only carbon & hydrogen (petroleum; lipid ‘tails’) Covalent bonding; nonpolar High energy storage Isomers (same molecular formula, but different structure & properties) • structural~differing covalent bonding arrangement • geometric~differing spatial arrangement • enantiomers~mirror images pharmacological industry (thalidomide) Figure 4.6 Three types of isomers Functional Groups, I • Attachments that replace one or more of the hydrogens bonded to the carbon skeleton of the hydrocarbon • Each has a unique property from one organic to another • Hydroxyl Group H bonded to O; alcohols; polar (oxygen); solubility in water • Carbonyl Group • C double bond to O; At end of skeleton: aldehyde Otherwise: ketone Functional Groups, II • Carboxyl Group O double bonded to C to hydroxyl; carboxylic acids; covalent bond between O and H; polar; dissociation, H ion • Amino Group N to 2 H atoms; amines; acts as a base (+1) Functional Groups, III • Sulfhydral Group sulfur bonded to H; thiols • Phosphate Group phosphate ion; covalently attached by 1 of its O to the C skeleton; Polymers • Covalent monomers • Condensation reaction (dehydration reaction): One monomer provides a hydroxyl group while the other provides a hydrogen to form a water molecule • Hydrolysis: bonds between monomers are broken by adding water (digestion) D:\ImageLibrary1-17\05Macromolecules\05-02Macromolecules.mov Carbohydrates, I • Monosaccharides √ CH2O formula; √ multiple hydroxyl (-OH) groups and 1 carbonyl (C=O) group: aldehyde (aldoses) sugar ketone sugar √ cellular respiration; √ raw material for amino acids and fatty acids Carbohydrates • Functions: Energy source Provide building material (structural role) • Contain carbon, hydrogen and oxygen in a 1:2:1 ratio • Varieties: monosaccharides, disaccharides, and polysaccharides Carbohydrates, II • Disaccharides √ glycosidic linkage (covalent bond) between 2 monosaccharides; √ covalent bond by dehydration reaction • Sucrose (table sugar) √ most common disaccharide Figure 5.5 Examples of disaccharide synthesis Carbohydrates, III • Polysaccharides Storage: Starch~ glucose monomers Plants: plastids Animals: glycogen • Polysaccharides Structural: Cellulose~ most abundant organic compound; Chitin~ exoskeletons; cell walls of fungi; surgical thread Lipids • • • • • • • • No polymers; glycerol and fatty acid Fats, phospholipids, steroids Hydrophobic; H bonds in water exclude fats Carboxyl group = fatty acid Non-polar C-H bonds in fatty acid ‘tails’ Ester linkage: 3 fatty acids to 1 glycerol (dehydration formation) Triacyglycerol (triglyceride) Saturated vs. unsaturated fats; single vs. double bonds Triglycerides: Long-Term Energy Storage • Fatty acids are either unsaturated or saturated. Unsaturated - one or more double bonds between carbons GOOD type of fat • Tend to be liquid at room temperature – Example: plant oils Saturated - no double bonds between carbons • Tend to be solid at room temperature BAD FAT – Examples: butter, lard 15 Phospholipids • 2 fatty acids instead of 3 (phosphate group) • ‘Tails’ hydrophobic; ‘heads’ hydrophilic • Micelle (phospholipid droplet in water) • Bilayer (double layer); cell membranes Steroids • Lipids with 4 fused carbon rings • Ex: cholesterol: cell membranes; precursor for other steroids (sex hormones) Proteins • Importance: instrumental in nearly everything organisms do; 50% dry weight of cells; most structurally sophisticated molecules known • Monomer: amino acids (there are 20) ~ carboxyl (-COOH) group, amino group (NH2), H atom, variable group (R)…. • Variable group characteristics: polar (hydrophilic), nonpolar (hydrophobic), acid or base • Three-dimensional shape (conformation) • Polypeptides (dehydration reaction): peptide bonds~ covalent bond; carboxyl group to amino group (polar) 3.4 Proteins • Proteins are polymers of amino acids linked together by peptide bonds. A peptide bond is a covalent bond between amino acids. • Two or more amino acids joined together are called peptides. Long chains of amino acids joined together are called polypeptides. • A protein is a polypeptide that has folded into a particular shape and has function. 20 Functions of Proteins • Metabolism Most enzymes are proteins that act as catalysts to accelerate chemical reactions within cells. • Support Keratin and collagen • Transport Hemoglobin and membrane proteins • Defense Antibodies • Regulation Hormones are regulatory proteins that influence the metabolism of cells. • Motion Muscle proteins and microtubules 21 Synthesis and Degradation of a Peptide Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. amino group amino acid Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. amino group peptide bond acidic group dehydration reaction hydrolysis reaction amino acid amino acid dipeptide water Levels of Protein Structure • Proteins cannot function properly unless they fold into their proper shape. When a protein loses it proper shape, it said to be denatured. • Exposure of proteins to certain chemicals, a change in pH, or high temperature can disrupt protein structure. • Proteins can have up to four levels of structure: Primary Secondary Tertiary Quaternary 24 Four Levels of Protein Structure Primary • The sequence of amino acids Secondary • Characterized by the presence of alpha helices and beta (pleated) sheets held in place with hydrogen bonds Tertiary • Final overall three-dimensional shape of a polypeptide • Stabilized by the presence of hydrophobic interactions, hydrogen bonding, ionic bonding, and covalent bonding Quaternary • Consists of more than one polypeptide 25 Primary Structure • Conformation: Linear structure • Molecular Biology: each type of protein has a unique primary structure of amino acids • Ex: lysozyme • Amino acid substitution: hemoglobin; sickle-cell anemia Secondary Structure • Conformation: coils & folds (hydrogen bonds) • Alpha Helix: coiling; keratin • Pleated Sheet: parallel; silk Tertiary Structure • Conformation: irregular contortions from R group bonding hydrophobic disulfide bridges hydrogen bonds ionic bonds Quaternary Structure • Conformation: 2 or more polypeptide chains aggregated into 1 macromolecule collagen (connective tissue) hemoglobin Nucleic Acids, I • • • • Deoxyribonucleic acid (DNA) Ribonucleic acid (RNA) DNA->RNA->protein Polymers of nucleotides (polynucleotide): nitrogenous base pentose sugar phosphate group • Nitrogenous bases: pyrimidines~cytosine, thymine, uracil purines~adenine, guanine 3.5 Nucleic Acids • Nucleic acids are polymers of nucleotides. • Two varieties of nucleic acids: DNA (deoxyribonucleic acid) • Genetic material that stores information for its own replication and for the sequence of amino acids in proteins. RNA (ribonucleic acid) • Perform a wide range of functions within cells which include protein synthesis and regulation of gene expression 31 Structure of a Nucleotide • Each nucleotide is composed of three parts: A phosphate group A pentose sugar A nitrogen-containing (nitrogenous) base • There are five types of nucleotides found in nucleic acids. DNA contains adenine, guanine, cytosine, and thymine. RNA contains adenine, guanine, cytosine, and uracil. • Nucleotides are joined together by a series of dehydration synthesis reactions to form a linear molecule called a strand. 32 Nucleotides Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. phosphate P C O 5' 4' S 1' 2' 3' pentose sugar nitrogencontaining base Figure 5.28 DNA cell RNA protein: a diagrammatic overview of information flow in a Nucleic Acids, II • Pentoses: – ribose (RNA) – deoxyribose (DNA) – nucleoside (base + sugar) • Polynucleotide: – phosphodiester linkages (covalent); phosphate + sugar Nucleic Acids, III • Inheritance based on DNA replication • Double helix (Watson & Crick - 1953) H bonds~ between paired bases van der Waals~ between stacked bases • A to T; C to G pairing • Complementary Structure of DNA and RNA The backbone of the nucleic acid strand is composed of alternating sugar-phosphate molecules. RNA is predominately a single-stranded molecule. DNA is a double-stranded molecule. • DNA is composed of two strands held together by hydrogen bonds between the nitrogencontaining bases. The two strands twist around each other to form a double helix. – Adenine hydrogen bonds with thymine – Cytosine hydrogen bonds with guanine • The bonding between the nucleotides in DNA is referred to as complementary base pairing. 37 A Special Nucleotide: ATP • ATP (adenosine triphosphate) is composed of adenine, ribose, and three phosphates. • ATP is a high-energy molecule due to the presence of the last two unstable phosphate bonds. • Hydrolysis of the terminal phosphate bond yields: The molecule ADP (adenosine diphosphate) An inorganic phosphate Energy to do cellular work • ATP is called the energy currency of the cell. 38 ATP Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a. adenosine triphosphate c. NH2 NH2 N N N H2O P N adenosine b. P P triphosphate ATP N N N P N adenosine P diphosphate ADP c: © Jennifer Loomis / Animals Animals / Earth Scenes + P phosphate + ENERGY