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Chapter 3 The Molecules of Cells PowerPoint Lectures for Biology: Concepts and Connections, Fifth Edition – Campbell, Reece, Taylor, and Simon Lectures by Chris Romero Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Got Lactose? • Lactose intolerance illustrates the importance of biological molecules to the functioning of living cells and to human health • Molecular interactions, such as those between the gene for lactase production, the enzyme lactase, and the milk sugar lactose, drive all biological processes Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings INTRODUCTION TO ORGANIC COMPOUNDS 3.1 Life's molecular diversity is based on the properties of carbon • Organic compounds contain at least one carbon atom • Covalent bonding enables carbon to form complex structures – A carbon atom has four electrons in its outer shell – To complete the shell, it can form four covalent bonds – The way bonding occurs among atoms determines the overall shape of the molecule Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 3-1a Structural formula Ball-and-stick model Space-filling model Methane The 4 single bonds of carbon point to the corners of a tetrahedron. LE 3-1b Ethane Propane Carbon skeletons vary in length. LE 3-1c Butane Isobutane Skeletons may be unbranched or branched. LE 3-1d 1-Butene 2-Butene Skeletons may have double bonds, which can vary in location. LE 3-1e Cyclohexane Benzene Skeletons may be arranged in rings. Animation: Carbon Skeletons Animation: Isomers Animation: L-Dopa Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Hydrocarbons are composed of only hydrogen and carbon – A series of covalently bonded carbons forms the carbon skeleton of the molecule – Isomers are molecules with the same molecular formula but different structures and properties Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 3.2 Functional groups help determine the properties of organic compounds • Functional groups are groups of atoms attached to the carbon skeleton of molecules – Usually participate in chemical reactions – Give organic molecules their particular properties Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 3-2 Estradiol Female lion Testosterone Male lion • Five main functional groups are important in the chemistry of life: – Hydroxyl group – Carbonyl group – Carboxyl group – Amino group – Phosphate group • These groups are all polar and make compounds containing them hydrophilic (waterloving) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 3.3 Cells make a huge number of large molecules from a small set of small molecules • Four main classes of biological macromolecules – Carbohydrates – Lipids – Proteins – Nucleic acids Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Cells make the most of their large molecules by joining smaller organic monomers into chains called polymers – Monomers are usually linked by dehydration reactions • A water molecule is removed Animation: Polymers Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 3-3a Short polymer Unlinked monomer Dehydration reaction Longer polymer – Polymers are broken down to monomers by the reverse process, hydrolysis • A water molecule is added Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 3-3b Hydrolysis CARBOHYDRATES 3.4 Monosaccharides are the simplest carbohydrates • Monosaccharides (single sugars) are carbohydrate monomers • A monosaccharide has a formula that is a multiple of CH2O – Contains hydroxyl groups and a carbonyl group – May be isomers, such as glucose and fructose – May take chain or ring forms Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 3-4b Glucose Fructose LE 3-4c Structural formula Abbreviated structure Simplified structure 3.5 Cells link two single sugars to form disaccharides • Two monosaccharides can join to form a disaccharide – Linked by a dehydration reaction – Example: two glucose monomers form the disaccharide maltose Animation: Disaccharides Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 3-5 Glucose Glucose Maltose CONNECTION 3.6 How sweet is sweet? • We perceive a sweet taste when a chemical binds to the sweet receptor on the tongue – The structure of a compound determines how well it fits into a receptor – The more strongly the chemical binds to the receptor, the sweeter it is perceived to be – The chemical can be sugar or another compound, such as aspartame Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 3.7 Polysaccharides are long chains of sugar units • Polysaccharides are polymers of monosaccharides linked together by dehydration reactions • Some polysaccharides are storage molecules – Starch in plants – Glycogen in animals • Some polysaccharides serve as structural compounds – Cellulose in plants Animation: Polysaccharides Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 3-7 Starch granules in potato tuber cells Glycogen granules in muscle tissues Cellulose fibrils in a plant cell wall Cellulose molecules STARCH Glucose monomer GLYCOGEN CELLULOSE LIPIDS 3.8 Fats are lipids that are mostly energy-storage molecules • Lipids are diverse compounds consisting mainly of carbon and hydrogen atoms – Linked by nonpolar covalent bonds – Hydrophobic (water-fearing) Animation: Fats Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Fats, also called triglycerides, are lipids whose main function is energy storage – Polymers of fatty acids (usually three molecules) and one glycerol molecule – Formed by dehydration reactions Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Saturated fatty acids – Contain the maximum number of hydrogens – Have no double bonds between carbons • Unsaturated fatty acids – Contain fewer than the maximum possible hydrogens – Have double bonds between carbons • Oils are liquid fats Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 3.9 Phospholipids, waxes, and steroids are lipids with a variety of functions – Phospholipids – Contain two fatty acid groups and the element phosphorus – Are a major component of cell membranes • Waxes – Consist of a single fatty acid linked to an alcohol – Form waterproof coatings Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Steroids – Have backbones bent into rings, as in cholesterol – Are often hormones or the basis of hormones Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings CONNECTION 3.10 Anabolic steroids pose health risks • Anabolic steroids are natural and synthetic variants of the male hormone testosterone – Build up bone and muscle mass – Can cause serious health problems Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PROTEINS 3.11 Proteins are essential to the structures and activities of life • A protein is a polymer constructed from amino acid monomers • The structure of the protein determines its function • The seven major classes of protein are – Structural: hair, cell cytoskeleton – Contractile: producers of movement in muscle and other cells Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings – Storage: sources of amino acids, such as egg white – Defense: antibodies, membrane proteins – Transport: carriers of molecules such as hemoglobin, membrane proteins – Signaling: hormones, membrane proteins – Enzymes: regulators of the speed biochemical reactions Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Animation: Structural Proteins Animation: Storage Proteins Animation: Transport Proteins Animation: Receptor Proteins Animation: Contractile Proteins Animation: Defensive Proteins Animation: Enzymes Animation: Hormonal Proteins Animation: Sensory Proteins Animation: Gene Regulatory Proteins Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 3.12 Proteins are made from amino acids linked by peptide bonds • Protein diversity is based on different arrangements of a common set of 20 amino acid monomers • Each amino acid contains – An amino group – A carboxyl group – One of twenty functional ("R") groups • The three groups and a hydrogen atom are bonded to a central "alpha" carbon Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 3-12a Amino group Carboxyl (acid) group • The structure of the R group determines the specific properties of each amino acid • An amino acid may be hydrophobic or hydrophilic, depending on the characteristics of the R group Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 3-12b Leucine (Leu) Hydrophobic Serine (Ser) Aspartic acid (Asp) Hydrophilic • Cells link amino acids together by dehydration synthesis • The bonds between amino acid monomers are called peptide bonds • Dipeptides are two amino acids long; polypeptides are from several to more than a thousand amino acids long Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 3-12c Carboxyl group Peptide bond Amino group Dehydration reaction Amino acid Amino acid Dipeptide 3.13 A protein's specific shape determines its function • A protein consists of one or more polypeptide chains spontaneously folded into a unique shape Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 3-13 Groove Groove • The folding of a polypeptide creates grooves that enable other molecules to bind to it • In denaturation, chemical or physical changes can cause proteins to lose their shape and thus their specific function Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 3.14 A protein's shape depends on four levels of structure • Primary structure: the unique sequence of amino acids forming the polypeptide • Secondary structure: the coiling or folding of the chain, stabilized by hydrogen bonding – May be alpha helix or pleated sheet (which dominates the silk protein of a spider's web) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Tertiary structure: the overall three-dimensional shape of the polypeptide • Quaternary structure: the association of two or more polypeptide chains (subunits) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 3-14a Levels of Protein Structure Amino acids LE 3-14b Levels of Protein Structure Amino acids Hydrogen bond Alpha helix Pleated sheet LE 3-14c Levels of Protein Structure Amino acids Hydrogen bond Alpha helix Polypeptide (single subunit of transthyretin) Pleated sheet LE 3-14d Levels of Protein Structure Amino acids Hydrogen bond Alpha helix Polypeptide (single subunit of transthyretin) Transthyretin, with four identical polypeptide subunits Pleated sheet Animation: Protein Structure Introduction Animation: Primary Protein Structure Animation: Secondary Protein Structure Animation: Tertiary Protein Structure Animation: Quarternary Protein Structure Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Collagen is an example of a protein with a quaternary structure – Three subunits wound into a helix – Structure provides great strength to long fibers Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings TALKING ABOUT SCIENCE 3.15 Linus Pauling contributed to our understanding of the chemistry of life • Felt that the study of individual parts must come first, then putting the parts together • Began his career by studying chemical bonding • First described the alpha helix and pleated sheet protein structures • Discovered how abnormal hemoglobin causes sickle cell disease • Won two Nobel prizes, for chemistry and for peace (for helping produce a nuclear test ban treaty) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings NUCLEIC ACIDS 3.16 Nucleic acids are information-rich polymers of nucleotides • There are two types of nucleic acid-DNA and RNA • Nucleic acids are polymers of nucleotide monomers composed of – A five-carbon sugar – A phosphate group – A nitrogenous base-adenine (A), thymine (T), cytosine ( C), and guanine (G) in DNA; A, G, C, and uracil (U) in RNA Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 3-16a Nitrogenous base (A) Phosphate group Sugar • Nucleotide monomers are formed into a polynucleotide with a sugar-phosphate backbone and attached nitrogenous bases Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 3-16b Nucleotide Sugar-phosphate backbone • Hydrogen bonding between nitrogenous bases creates the final structure of the nucleic acid – RNA usually consists of a single polynucleotide strand – DNA is a double helix • Two polynucleotides are twisted around each other • Nitrogenous bases protruding from the backbone pair with each other, A with T and G with C Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 3-16c Base pair – Specific sequences of DNA make up genes that program the amino acid sequences of proteins Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings