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Chapter 4: Carbon Carbon • Overview: Carbon—The Backbone of Biological Molecules • All living organisms are made up of chemicals based mostly on the element carbon • Organic chemistry is the study of carbon compounds Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings The Formation of Bonds with Carbon Carbon has four valence electrons This allows it to form four covalent bonds with a variety of atoms Versatility of Carbon • The bonding versatility of carbon • Allows it to form many diverse molecules, including carbon skeletons Name and Comments Molecular Structural Formula Formula H (a) Methane CH4 H C H H (b) Ethane H H C2H6 H C C H H H (c) Ethene (ethylene) H C2H4 Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings H C C H H Ball-andStick Model SpaceFilling Model Common Bonding Partners of Carbon • The electron configuration of carbon • Gives it covalent compatibility with many different elements Hydrogen Oxygen Nitrogen Carbon (valence = 1) (valence = 2) (valence = 3) (valence = 4) N C H O Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Which of the structures in this figure is an impossible covalently bonded molecule? a. A b. B C c. C d. D e. E Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Molecular Diversity Arising from Carbon Skeleton Variation • Carbon chains • Form the skeletons of most organic molecules • Vary in length and shape (a) Length H H H C C H H H Ethane H H H H C C C H H H H Propane H H C H H H H H H H (b) Branching H C C C C H H C C C H H H H H H H H 2-methylpropane Butane (commonly called isobutane) H H H H H H H H (c) Double bonds H H C C C C H C C C C H H H H H 1-Butene 2-Butene H H H H C H H C C H C H (d) Rings H C C H H C C H H C C C Cyclohexane Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Benzene Hydrocarbons Hydrocarbons Are molecules consisting of only carbon and hydrogen The bonds between the C and H atoms are non-polar covalent This makes hydrocarbons hydrophobic Hydrocarbons • Hydrocarbons • Are found in many of a cell’s organic molecules Fat droplets (stained red) (a) A fat molecule Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings 100 µm (b) Mammalian adipose cells Isomers Isomers Are molecules with the same molecular formula but different structures and properties Isomers • Three types of isomers are • Structural • Geometric • Enantiomers (a) Structural isomers (b) Geometric isomers H H H H H H C C C C C H H H H H H X C C H (c) Enantiomers H H C H H C H H H H C C C H H H H H X X H CO2H C H CH3 Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings C C X H CO2H NH2NH2 C CH3 H Why are Enantiomeric isomers important? • Enzymes distinguish between enantiomers! H (a) Structural isomers H H H H H H C C C C C H H X (b) Geometric isomers H H H H H H Enzyme X activity = C C 100 % H Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings C C C NH2 CH3 C CO2H C H C H H H C H H H Enzyme H X activity = C C X0 % H CO2H (c) Enantiomers H H H H NH2 CH3 H Structure and Function Subtle changes in structure can dramatically affect the molecule’s function The Functional Groups Functional groups Are the chemically reactive groups of atoms within an organic molecule They behave consistently and characteristically, giving unique properties to the molecules possessing them. Six functional groups are important in the chemistry of life Hydroxyl Carbonyl Carboxyl Amino Sulfhydryl Phosphate Functional Groups FUNCTIONAL GROUP HYDROXYL CARBONYL CARBOXYL O OH (may be written HO C C OH ) STRUCTURE In a hydroxyl group (—OH), a hydrogen atom is bonded to an oxygen atom, which in turn is bonded to the carbon skeleton of the organic molecule. (Do not confuse this functional group with the hydroxide ion, OH–.) O The carbonyl group ( CO) consists of a carbon atom joined to an oxygen atom by a double bond. Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings When an oxygen atom is doublebonded to a carbon atom that is also bonded to a hydroxyl group, the entire assembly of atoms is called a carboxyl group (— COOH). Functional Groups CARBONYL HYDROXYL NAME OF COMPOUNDS Alcohols (their specific names usually end in -ol) EXAMPLE H H H C C H H Ketones if the carbonyl group is Carboxylic acids, or organic within a carbon skeleton acids Aldehydes if the carbonyl group is at the end of the carbon skeleton H OH CARBOXYL H C H C H H Ethanol, the alcohol present in alcoholic beverages H O C C H O C OH H H Acetone, the simplest ketone H H H C C H H O C Propanal, an aldehyde Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings H Acetic acid, which gives vinegar its sour tatste Functional Groups AMINO SULFHYDRYL H O SH N (may be written HS H The amino group (—NH2) consists of a nitrogen atom bonded to two hydrogen atoms and to the carbon skeleton. PHOSPHATE ) O P OH OH The sulfhydryl group consists of a sulfur atom bonded to an atom of hydrogen; resembles a hydroxyl group in shape. Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings In a phosphate group, a phosphorus atom is bonded to four oxygen atoms; one oxygen is bonded to the carbon skeleton; two oxygens carry negative charges; abbreviated P . Functional Groups H O C HO C H PHOSPHATE SULFHYDRYL AMINO H N H H Glycine H H C C H H OH OH H SH H C C C H H H O O P O O Ethanethiol Because it also has a carboxyl group, glycine is both an amine and a carboxylic acid; compounds with both groups are called amino acids. Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Glycerol phosphate Effect of Different Functional Groups • Functional groups give organic molecules distinctive chemical properties Estradiol OH CH3 HO Female lion OH CH3 CH3 O Male lion Copyright © 2004 Pearson Education, Inc. publishing as Benjamin Cummings Testosterone Key Points of Chapter 4 Organic chemistry is the study of carbon compounds Carbon atoms can form diverse molecules by bonding to 4 other atoms Functional groups are the parts of molecules involved in chemical reactions and behave chemically in expected manners Chapter 4 Essay Question Discuss the biological importance of each of the following organic compounds in relation to cellular structure and function in plants and animals. a. Carbohydrates b. Proteins c. Lipids d. Nucleic acids