Biology Eleventh Edition Chapter 3: Chemistry of Life

BIOLOGY ELEVENTH EDITION Chapter 3 The Chemistry of Life: Organic Compounds © 2019 Cengage. All rights reserved.  Organic Compounds...

BIOLOGY ELEVENTH EDITION Chapter 3 The Chemistry of Life: Organic Compounds © 2019 Cengage. All rights reserved.  Organic Compounds Those in which carbon atoms are covalently bonded to one another to form the backbone of the molecule. – Organic compounds are extraordinarily diverse: The carbon atom forms bonds with more different elements than any other type of atom – The addition of chemical groups containing atoms of other elements—especially oxygen, nitrogen, phosphorus, and sulfur—can profoundly change the properties of an organic molecule. – More than five million organic compounds have been identified, including large macromolecules made up of modular subunits (Carbohydrates, Lipids, Proteins, and Nucleic acids) © 2019 Cengage. All rights reserved. 3.1 Carbon Atoms and Organic Molecules (1 of 2) A carbon atom can complete its valence shell by forming a total of four covalent bonds Carbon-to-carbon bonds are strong and not easily broken (But they are not so strong that it would be impossible for cells to break them) – Three types: single, double, and triple © 2019 Cengage. All rights reserved.  3.1 Carbon Atoms and Organic Molecules (1 of 2) Hydrocarbons (organic compounds consisting only of carbon and hydrogen) can exist as unbranched or branched chains, or as rings Chains Rings Note that each Double carbon atom forms bonds four covalent bonds, producing a wide variety of molecular shapes and sizes. Branched chains Joined rings and chains © 2019 Cengage. All rights reserved. 3.1 Carbon Atoms and Organic Molecules (2 of 2) The shape of a molecule can determine its biological properties and function – Carbon atoms link to one another and to other atoms to produce various 3-D shapes (not a single plain)  Freedom of rotation around each carbon-to-carbon single bond permits organic molecules to assume a variety of shapes (see Methane below) Double and triple bonds do not allow rotation © 2019 Cengage. All rights reserved.  Isomers Have The Same Molecular Formula But Different Structures The same components usually can link in more than one pattern, generating a wide variety of molecular shapes (one reason for the great number of possible carbon-containing compounds) Isomers are compounds with the same molecular formulas but different structures and properties – Isomers do not have identical physical or chemical properties and may have different common names. – Usually, one isomer is biologically active; another is not (which means cells can distinguish between isomers) © 2019 Cengage. All rights reserved. Three Types of Isomers A. Structural isomers: differ in covalent arrangements of atoms B. Geometric isomers: identical in arrangement of covalent bonds but different in spatial arrangement of atoms (cis, trans due to the carbon double bond) C. Enantiomers: isomers that are mirror images of each other (asymmetrical carbon when bonding to 4 different atoms) © 2019 Cengage. All rights reserved. Functional Groups Change the Properties of Organic Molecules (1 of 5) The addition of various combinations of atoms generates a vast array of molecules with different properties. Hydrocarbons lack distinct charged regions, thus they are insoluble in water, and cluster together – Creates hydrophobic interactions (Hydrocarbons interact with water, but much more weakly than the water molecules cohere to one another through hydrogen bonding) Functional group: a group of atoms that help determine the types of chemical reactions and associations in which the compound participates. Replacing one or more hydrogen with a functional group dramatically changes the characteristics of an organic molecule – Polar and ionic functional groups are hydrophilic © 2019 Cengage. All rights reserved. Functional Groups Change the Properties of Organic Molecules (2 of 5) The types and arrangement of functional groups determine the properties of the major classes of biologically important organic compounds (carbohydrates, lipids, proteins, and nucleic acids) Chemical behavior can be predicted by the type of functional groups Symbol R is used to represent the remainder of the molecule of which each functional group is a part Methyl group: a nonpolar hydrocarbon group (R—CH3) Hydroxyl group (R—OH): polar because of a strongly electronegative oxygen atom © 2019 Cengage. All rights reserved. Functional Groups Change the Properties of Organic Molecules (2 of 5) Carbonyl group (C=O): a carbon atom that has a double covalent bond with an oxygen atom – Example: aldehyde (at least one H atom) and ketone (no H atoms) © 2019 Cengage. All rights reserved. Functional Groups Change the Properties of Organic Molecules (3 of 5) Carboxyl group (R—COOH): a carbon joined by a double covalent bond to an oxygen, and by a single covalent bond to another oxygen bonded to a hydrogen – Weakly acidic; Ionized carboxyl group releases the hydrogen ion and has 1 unit of negative charge (R— COO−+ H+) – Essential constituents of amino acids © 2019 Cengage. All rights reserved. Functional Groups Change the Properties of Organic Molecules (4 of 5) Amino group (R—NH2): a nitrogen atom covalently bonded to two hydrogen atoms – Ionized amino group accepts a hydrogen ion (proton) and has one unit of positive charge (R—NH3+) – Components of amino acids and nucleic acids © 2019 Cengage. All rights reserved. Functional Groups Change the Properties of Organic Molecules (5 of 5) Phosphate group (R—PO4H2): can release one or two hydrogen ions due to oxygen's electronegativity, producing ionized forms with one or two units of negative charge (weakly acidic) – Makes up nucleic acids and certain lipids © 2019 Cengage. All rights reserved. Functional Groups Change the Properties of Organic Molecules (5 of 5) Sulfhydryl group (R—SH): an atom of sulfur covalently bonded to hydrogen; found in molecules called thiols – Important in proteins © 2019 Cengage. All rights reserved. Many Biological Molecules Are Polymers (1 of 3) Macromolecules: consist of thousands of atoms – Make up proteins and nucleic acids Most macromolecules are polymers, produced by linking small organic compounds called monomers – Words are combination of 26 alphabet letters – Monomers can be grouped to form an almost infinite variety of larger molecules. – 20 monomers (amino acids) are linked end to end in countless ways to form the polymers proteins © 2019 Cengage. All rights reserved. Many Biological Molecules Are Polymers (2 of 3) Polymers can be degraded to component monomers by hydrolysis reactions (“to break with water”) – Hydrogen from a water molecule attaches to one monomer, and hydroxyl from water attaches to the adjacent monomer (driven by an enzyme A) Monomers become covalently linked by condensation reactions – The equivalent of a molecule of water is removed during condensation reactions that combine monomers (driven by an enzyme B) – Dehydration synthesis = condensation reaction – The synthesis of a polymer is not simply the reverse of hydrolysis: condensation requires energy and is regulated by different enzymes. © 2019 Cengage. All rights reserved. Many Biological Molecules Are Polymers (3 of 3) Condensation Enzyme B Hydrolysis Monomer Monomer Enzyme A Dimer © 2019 Cengage. All rights reserved.  3.2 Carbohydrates Carbohydrates contain carbon, hydrogen and oxygen atoms in a ratio of approximately 1C:2H:1O (CH2O)n – Sugars and starches – Can contain:  One sugar unit (monosaccharides)  Two sugar units (disaccharides)  Many sugar units (polysaccharides) – Cellulose © 2019 Cengage. All rights reserved.  Monosaccharides Are Simple Sugars (1 of 3) Contain 3 to 7 carbon atoms – In a monosaccharide, a hydroxyl group is bonded to each carbon except one; that carbon is double-bonded to an oxygen atom, forming a carbonyl group – Aldehyde: carbonyl group is at the end of the chain – Ketone: carbonyl group is at any other position – Other examples: Triose (glyceraldehyde, dihydroxyacetone), Pentose (ribose, deoxyribose), Hexose (glucose, fructose, galactose) © 2019 Cengage. All rights reserved.  Monosaccharides Are Simple Sugars (1 of 3) The numbering of the carbon skeleton of a sugar begins with the carbon at or nearest the carbonyl end of the open chain The large number of polar hydroxyl groups, plus the carbonyl group, gives a monosaccharide hydrophilic properties © 2019 Cengage. All rights reserved.  Glucose is the most abundant monosaccharide (2 of 3) Glucose, C6H12O6, is the most abundant monosaccharide and used as the primary energy source – used as the primary energy source during cellular respiration – used in the synthesis of other types of compounds such as amino acids and fatty acids – important in metabolism (so maintaining its concentration at relatively constant levels in the blood of humans and other animals is important) – Glucose (an aldehyde) and fructose (a ketone), due to these differences, the two sugars have different properties (fructose found in honey and some fruits, tastes sweeter than glucose) © 2019 Cengage. All rights reserved. Glucose can be α-Glucose or β-Glucose depending on its structure (3 of 3) Glucose in solution (as in the cell) typically exists as a ring of five carbons and one oxygen When this hydroxyl When this hydroxyl group group is on the is on the same side of opposite side of CH2OH side group CH2OH side group © 2019 Cengage. All rights reserved.  Disaccharides Consist of Two Monosaccharide Units Disaccharide (two sugar) – Two monosaccharide rings joined by a glycosidic linkage (covalent linkage joining two sugars), consisting of a central oxygen covalently bonded to two carbons, one in each ring Fig. 3-8. Sucrose © 2019 Cengage. All rights reserved.  Disaccharides Consist of Two Monosaccharide Units Common disaccharides – Maltose (malt sugar): 2 covalently linked α-glucose units – Sucrose (table sugar): 1 glucose + 1 fructose – Lactose (milk sugar): 1 glucose + 1 galactose © 2019 Cengage. All rights reserved.  Polysaccharides Can Store Energy or Provide Structure (1 of 4) Polysaccharide – Macromolecule consisting of repeating units of simple sugars, usually glucose – Polysaccharide is the most abundant carbohydrates:  Starches: energy storage in plants  Glycogen: energy storage in animals  Cellulose: structural polysaccharide in plants – Those that can be easily broken down to their subunits are well suited for energy storage, whereas others make them particularly well suited to form stable structures. © 2019 Cengage. All rights reserved.  Polysaccharides Can Store Energy or Provide Structure (2 of 4) Amyloplasts Starch: the typical form of carbohydrate used for energy storage in plants, a polymer consisting of α-glucose subunits (α 1—4 glycosidic linkages), and occurs in two forms: – Amylose (unbranched chain) – Amylopectin (i.e. potato) (branched chain) Starch (purple stained) is stored in specialized organelle, amyloplasts, in cells of a butter cup root © 2019 Cengage. All rights reserved.  Polysaccharides Can Store Energy or Provide Structure (3 of 4) Glycogen – Glucose subunits (α 1—4 glycosidic linkages) stored as an energy source in animal tissues – Similar in structure to plant starch but more extensively branched and more water soluble – In vertebrates, glycogen is stored mainly in liver and muscle cells – Humans have enzymes that break α 1—4 glycosidic linkages © 2019 Cengage. All rights reserved.  Polysaccharides Can Store Energy or Provide Structure (4 of 4) Cellulose – Most abundant of carbohydrates – Insoluble polysaccharide composed of many joined Bundel of glucose molecules – cellulose Structural component of plants (fibers) – Humans lack enzymes to hydrolyze β 1—4 linkages of cellulose – Extensive hydrogen bonding of β-glucose subunits and among different cellulose molecules © 2019 Cengage. All rights reserved.  Some Modified and Complex Carbohydrates Have Special Roles Amino sugars galactosamine and glucosamine are compounds in which a hydroxyl group (—OH) is replaced by an amino group. Galactosamine is present in cartilage. Chitin: glycosidic bonds of N-acetyl glucosamine (NAG) subunits, main component of exoskeletons and the cell walls of fungi Glycoproteins: carbohydrate + protein, functional proteins secreted by cells [protein protection (mucus) or adherence) Glycolipids: carbohydrate + lipid, recognition compounds on surfaces of animal cells © 2019 Cengage. All rights reserved.  3.3 Lipids Lipids – Compounds soluble in nonpolar solvents, and relatively insoluble in water – Consist mainly of carbon and hydrogen, with few oxygen-containing functional groups (hydrophobic) – Biologically important groups of lipids include fats (triacylglycerols), phospholipids, carotenoids (orange and yellow plant pigments), steroids, and waxes  Used for energy storage, structural components of cell membranes, and in key hormones © 2019 Cengage. All rights reserved.  Triacylglycerol is Formed From Glycerol and Three Fatty Acids (1 of 2) Triacylglycerols (triglycerides or fats): glycerol + fatty acids – Most abundant lipids in living organisms – An economical form of reserve fuel storage (yield more than twice as much energy per gram as do carbs) – Consists of glycerol joined to three fatty acids – Carbs and proteins can be transformed by enzymes into fat and stored in the cells of adipose tissues in animals and in some seeds and fruits of plants Glycerol is a three-carbon alcohol with three hydroxyl (–OH) groups Fatty acid is a long, unbranched hydrocarbon chain with a carboxyl group (–COOH) at one end © 2019 Cengage. All rights reserved. Triacylglycerol is Formed From Glycerol and Three Fatty Acids (1 of 2) Glycerol and fatty acids are the components of fats. © 2019 Cengage. All rights reserved.  Triacylglycerol is Formed From Glycerol and Three Fatty Acids (2 of 2) Ester linkage: covalent linkage formed by the reaction of a carboxyl group and a hydroxyl group, with the removal of the equivalent of a water molecule (carbon to oxygen bond) Triacylglycerol: formed by a series of three ester linkages – First reaction yields a monoacylglycerol (monoglyceride) – Second yields a diacylglycerol (diglyceride) – Third yields a triacylglycerol (triglyceride) During digestion, triacylglycerols are hydrolyzed to produce fatty acids and glycerol © 2019 Cengage. All rights reserved.  Saturated and Unsaturated Fatty Acids Differ in Physical Properties (1 of 3) Fatty acids typically have an even number of carbon atoms − Butyric acid present in rancid butter: 4 carbons − Oleic acid: 18 carbons, the most widely distributed fatty acid in nature Saturated fatty acids – Contain max number of hydrogen atoms (palmitic acid) – Found in animal fat and solid vegetable shortening – Solid at room temperature due to van der Waals interactions © 2019 Cengage. All rights reserved.  Saturated and Unsaturated Fatty Acids Differ in Physical Properties (2 of 3) Unsaturated fatty acids – Include one or more adjacent pairs of carbon atoms joined by a double bond – They are not fully saturated with hydrogen – Tend to be liquid at room temperature © 2019 Cengage. All rights reserved.  Saturated and Unsaturated Fatty Acids Differ in Physical Properties (3 of 3) Each double bond produces a bend in the hydrocarbon chain that prevents close alignment with an adjacent chain, limiting van der Waals interactions – Monounsaturated fatty acids have one double bond (oleic acid) – Polyunsaturated fatty acids have more than one double bond (linoleic acid) © 2019 Cengage. All rights reserved.  Shapes of Fatty Acids Saturated Monounsaturated Polyunsaturated © 2019 Cengage. All rights reserved.  Saturated and Unsaturated Fatty Acids Hydrogenated or partially hydrogenated cooking oil – Converting unsaturated fatty acids to saturated fatty acids to make fat more solid at room temperature (margarine), less healthful to increase the risk of cardiovascular disease Trans fats – Artificial hydrogenation can produce a trans configuration: technically unsaturated form, but they mimic many of the properties of saturated fatty acids (no bend at the site of the double bond), more solid at room temperature than cis; increases risk of cardiovascular disease © 2019 Cengage. All rights reserved.  Phospholipids Are Components of Cell Membranes (1 of 2) Phospholipids are amphipathic lipids, with one hydrophilic end and one hydrophobic end – Hydrophilic head consists of a glycerol molecule, phosphate group and organic group like choline – Hydrophobic tail consists of two fatty acids The fatty acid portion of the molecule (containing the two hydrocarbon “tails”) is hydrophobic and not soluble in water, but the portion composed of glycerol, phosphate, and the organic base (the “head” of the molecule) is ionized and readily water soluble Phospholipids are basic components of cell membranes (phospholipid bilayer) © 2019 Cengage. All rights reserved. Phospholipids Are Components of Cell Membranes (2 of 2) © 2019 Cengage. All rights reserved. Phospholipids Are Components of Cell Membranes (2 of 2) A lipid bilayer forms when phospholipids interact with water © 2019 Cengage. All rights reserved. Carotenoids And Many Other Pigments Are Derived From Isoprene Units Carotenoids are orange and yellow plant pigments – Classified as oil because of being insoluble in water, with an oily consistency – Function in photosynthesis – Consist of 5-carbon hydrocarbon monomers (isoprene unit) Most animals convert carotenoids to vitamin A, which can be converted to the visual pigment retinal Mollusks, insects, and vertebrates have eyes that use retinal in the process of light reception. © 2019 Cengage. All rights reserved.  Steroids Contain Four Rings of Carbon Atoms A steroid consists of carbon atoms arranged in four attached rings A. Cholesterol: essential for cell membrane - Side chains distinguish one steroid from another - Synthesized from isoprene units B. Cortisol: steroid - Examples: cholesterol, bile salts, hormone secreted by reproductive hormones, cortisol, and adrenal gland other hormones - Plant cell membranes contain molecules similar to cholesterol: some of these plant steroids block the intestine’s © 2019 Cengage. All rights reserved. absorption of cholesterol