Structure and Function of Macromolecules Chapter 3 Versatility of carbon Carbon can form covalent bonds with many other atoms Carbon valence 4 Most frequently bonded to hydrogen other carbon atoms Diversity in biological molecules arises partly from variations in carbon skeletons functional groups Variety in carbon skeletons H H H H H H C C H H H H C C C H H H H Ethane Propane H H H H H H C H H H H C C C C H H H H H H C C C H H H H Butane 2 methylpropane isobutane a Length b Branching c Double bonds H H H H H H H H H C C C C H H H H C C C C H H H 1 Butene d Rings H H H H H H H C C C H C C H H C H H Cyclohexane 2 Butene H H C H C C H C C C H H Benzene Functional groups Carbon atoms can also form covalent bonds with other atoms most common important in biological molecules oxygen nitrogen phosphorus sulfur These are often arranged in functional groups attached to C skeleton Small variations in functional groups can have large effects on function Functional groups Functional groups most important in biological molecules Hydroxyl Carbonyl Carboxyl Amino Sulfhydryl Phosphate Methyl Functional groups 3 2 Properties Comments Polar O electronegative Hydrophilic Carbonyl group can be in middle or at end of molecule Functional groups 3 2 Properties Comments Acidic undergoes reversible ionization loses H Mostly ionized negatively charged at pH of cell Polar hydrophilic Basic undergoes reversible ionization gains H Mostly ionized positively charged at pH of cell Polar hydrophilic H N H N H H H Functional groups 3 2 Properties Comments Interaction between two sulfhydryl groups are critical for protein structure Role in protein regulation Acidic Always ionized at pH of cell Polar hydrophilic Critical for cellular energy transfers ATP Functional groups 3 2 Properties Comments nucleic acids others Not hydrophilic not reactive Methylation addition methyl group regulates gene expression hormone activity Four major classes of macromolecules Carbohydrates Nucleic acids Proteins Lipids Polymers long molecule consisting of many similar subunits called monomers linked by covalent bonds Have multiple functions in cells How do the structural features of macromolecules contribute to their cellular functions Synthesis and breakdown of polymers Synthesis of Polymers 3 3 H2O 2 HO Short polymer 3 H HO HO H Unlinked monomer Dehydration reaction HO H Longer polymer Polymerization synthesis of polymers from monomers Catalyzed by enzymes Requires energy Breakdown of Polymers 3 3 H2O HO H Longer polymer Hydrolysis reaction HO 2 Short polymer 3 H HO HO H Unlinked monomer Catalyzed by enzymes Releases energy Generates supply of monomers Polymer breakdown and synthesis in the body A Hydrolysis B Dehydration C Requires enzymes D Requires energy E Releases energy F Polymerization Breakdown Synthesis Carbohydrates slides15 24 of this file Carbohydrates Include both sugars small carbohydrates and their polymers Serve as energy storage and structural molecules Sugars Monosaccharides Smallest simplest sugars Serve as fuels building blocks of disaccharides and polysaccharides Molecular formula CH2O n Triose 3 C C3H6O3 Hexose 6 C C6H12O6 Suffix ose Length of C backbone Monosaccharides 3 4 Linear and ring structures of glucose 3 5 Synthesis of disaccharides 3 7a Disaccharides are formed from two monosaccharides by dehydration glycosidic linkage Polysaccharides Polysaccharides polymers of sugars Formed by polymerization dehydration Structure and function determined by monomer composition and the positions of glycosidic linkages Have energy storage and structural roles Storage polysaccharides starch and glycogen Chloroplast Mitochondria Starch granules 1 m 3 8 Glycogen granules 0 5 m Polymers of glucose Starch a plant polysaccharide Glycogen an animal polysaccharide Broken down to glucose by hydrolysis when energy needed Structural polysaccharides cellulose 3 9b Cellulose also a polymer of glucose major component of the rigid walls of plant cells provides structural support most abundant organic compound on Earth target of biofuels research Cotton Importance of different types of glycosidic linkages 3 8 3 9 Starch and cellulose are both polymers of glucose but have different glycosidic linkages Specifically recognized and hydrolyzed by human enzymes Usable form of energy for humans Cannot be hydrolyzed by humans Can be hydrolyzed by some other organisms Gut bacteria produce cellulase an enzyme that digests cellulose Fungi are key producers of cellulase biomass recycling Chitin exoskeletons of insects and crustaceans Nucleic acids slides 25 30 of this file Nucleic acids store and transmit hereditary information Two types Deoxyribonucleic acid DNA double stranded Ribonucleic acid RNA single stranded Both are polymers of nucleotides Nucleotides 3 21 and 3 22a Nucleotides monomer building blocks of nucleic acids Nucleic acid or polynucleotide Nucleotides 3 21 and 3 22b Nucleotides monomer building blocks of nucleic acids Hydrogen bonding in DNA 3 20 Hydrogen bonding in DNA 14 9 Proteins Encoded by genes Composed of amino acids Nucleotide sequence of gene specifies amino acid sequence of protein More than 50 of the dry mass of most cells Most structurally complex macromolecules Each protein has a unique structure shape that confers a unique function Huge array of functions Functions of proteins Enzymes Defense Function Selective acceleration of chemical reactions Example Digestive enzymes catalyze the hydrolysis of bonds in food molecules Function Protection against disease Example Antibodies inactivate and help destroy viruses and bacteria Antibodies Enzyme Virus Bacterium Storage Transport proteins Function Storage of amino acids Examples Casein the protein of milk is the major source of amino acids for baby mammals Plants have storage proteins in their seeds Ovalbumin is the protein of egg white used as an amino acid source for the developing embryo Function Transport of substances Examples Hemoglobin the iron containing protein of vertebrate blood transports oxygen from the lungs to other parts of the body Other proteins transport molecules across cell membranes Transport protein Ovalbumin Amino acids for embryo Cell membrane Functions of proteins Cell regulation hormones Cell regulation receptors Function Coordination of an organism s activities Example Insulin a hormone secreted by the pancreas causes other tissues to take up glucose thus regulating blood sugar concentration High blood sugar Insulin secreted Normal blood