CARBON AND THE MOLECULAR DIVERSITY OF LIFE CHAPTER 4 CARBON AND THE MOLECULAR DIVERSITY OF LIFE

Overview: Carbon—The Backbone of Life Aside from water, the most biologically important molecules are carbon-based (organic). Although cells are 70–95% water, the rest consists mostly of carbon-based compounds Carbon is unparalleled in its ability to form large, complex, and diverse molecules Proteins, DNA, carbohydrates, and other molecules that distinguish living matter are all composed of carbon compounds

Concept 4.1: Organic chemistry is the study of carbon compounds A. Organic chemistry is the study of compounds that contain carbon 1. Organic compounds range from simple molecules to colossal ones 2. Most organic compounds contain hydrogen atoms in addition to carbon atoms

Concept 4.2: Carbon atoms can form diverse molecules by bonding to four other atoms Electron configuration is the key to an atom’s characteristics Electron configuration determines the kinds and number of bonds an atom will form with other atoms

A. The Formation of Bonds With Carbon 1. Carbon atom Atomic number 6 (6 protons, 6 electrons, 6 neutrons) 4 valance electrons Forms 4 covalent bonds usually with H, O, N, C Can form large, complex molecules 2. Carbon Dioxide (OCO) Source of carbon for all organic molecules found in organisms

B. Molecular Diversity Arising from Carbon Skeleton Variation 1. Covalent bonds link carbon atoms together in long chains that form the skeletal framework for organic molecules. 2. Carbon skeletons may vary in: Length Shape (straight chain, branched, ring) Number and location of double bonds Other elements covalently bonded to available sites 3. Variation contributes to complexity and diversity of organic molecules

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C. Hydrocarbons Hydrocarbons are organic molecules consisting of only carbon and hydrogen Many organic molecules, such as fats and fossil fuels, have hydrocarbon components Hydrocarbons can undergo reactions that release a large amount of energy Hydrocarbon chains are hydrophobic because C—C and C—H bonds are nonpolar.

Hydrocarbon

D. Isomers 1. Isomers are compounds with the same molecular formula but different structures and properties. 2. Three types of isomers: a. Structural Isomers Have different covalent arrangements of their atoms Number of possible isomers increases as C skeleton size increases Ex: C5 H13—3 isomers C8 H18—18 isomers C20 H42—366,319 isomers May differ in location of double bonds

Structural Isomers

b. Geometric isomers Have the same covalent arrangements but differ in spatial arrangements Result from the fact that double bonds will not allow the atoms they join to rotate freely about the axis of the bonds Subtle differences between isomers affects their biological activity

Geometric Isomers

Are isomers that are mirror images of each other c. Enantiomers Are isomers that are mirror images of each other Can occur when 4 different atoms or groups of atoms are bonded to the same carbon (asymmetric carbon) Usually one form is biologically active and its mirror image is not Important in the pharmaceutical industry Two enantiomers of a drug may have different effects 04_07Isomers_A.html

Enantiomers

Enantiomer 04_07L_Dopa_A.html

Concept 4.3: A small number of chemical groups are key to the functioning of biological molecules Distinctive properties of organic molecules depend not only on the carbon skeleton but also on the molecular components attached to it A number of characteristic groups are often attached to skeletons of organic molecules

A. The Chemical Groups Most Important in the Process of Life 1 A. The Chemical Groups Most Important in the Process of Life 1. Functional groups are the components of organic molecules that are most commonly involved in chemical reactions 2. The number and arrangement of functional groups give each molecule its unique properties 3. Functional group replaces an H bonded to the carbon of a hydrocarbon

4. The seven functional groups that are most 4. The seven functional groups that are most important in the chemistry of life: Hydroxyl group Carbonyl group Carboxyl group Amino group Sulfhydryl group Phosphate group Methyl group

Polar group, therefore it makes the molecule attached to water soluble 5. The Seven Functional Groups a. Hydroxyl Group (-OH) Consists of a hydrogen atom bonded to an oxygen atom, which is bonded to carbon H H | | H—C—C—OH R—OH Ethanol   Polar group, therefore it makes the molecule attached to water soluble Organic compounds with hydroxyl groups are called alcohols Names end in –ol

Consists of a carbon atom double-bonded to oxygen b. Carbonyl Group (-CO) Consists of a carbon atom double-bonded to oxygen Polar group, therefore it makes the molecule attached to water soluble Found in sugars If the carbonyl group is on the end of the carbon skeleton, the compound is an aldehyde  OH OH O O | | // // H—C—C—C R—C | | \ \ H H H H Glyceraldehyde 

If the carbonyl group is in the internal part of a carbon skeleton, the compound is a ketone H O H O | || | || H—C—C—C—H R—C—R | | H H Acetone

c. Carboxyl Group (-COOH) Consists of a carbon atom which is both double-bonded to an oxygen and single bonded to the oxygen of a hydroxyl group Polar group and water soluble Have acidic properties Compounds with this group are called carboxylic acids (organic acids) H O O | // // H—C—C R—C | \ \ H OH OH Acetic Acid  

Polar group and water soluble Weak base d. Amino Group (-NH2) Consists of a nitrogen atom bonded to two hydrogens and to the carbon skeleton Polar group and water soluble Weak base Organic compounds with this functional group are called amines H H H | / / H—C—N R—N | \ \ H H H

Contain both carboxyl and amino groups B. Amino Acids Contain both carboxyl and amino groups H H O \ | // N—C—C / | \ H R OH amino carboxyl

Consists of an atom of sulfur bonded to an atom of hydrogen e. Sulfhydryl Group (-SH) Consists of an atom of sulfur bonded to an atom of hydrogen Helps stabilize the structure of proteins Organic compounds with this functional group are called thiols  H H | | H—C—C—SH R—SH H H

Functional group which is the dissociated form of phosphoric acid f. Phosphate Group (H3PO4) Functional group which is the dissociated form of phosphoric acid Polar group and water soluble Acid properties Form organic phosphates Organic phosphates are important in cellular energy storage and transfer (ATP) OH OH H O O | | | || || H—C—C—C—O—P—O- R—O—P—O- | | | | | H H H O- O-  

ATP

Consists of a carbon bonded to 3 hydrogens g. Methyl Group (-CH3) Consists of a carbon bonded to 3 hydrogens May be attached to a carbon or to a different atom Not really a functional group because they are not reactive but may serve as important markers on organic molecules Can affect expression of genes H / —C—H \