4 Carbon and the Molecular Diversity of Life

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1 4 Carbon and the Molecular Diversity of Life CAMPBELL BIOLOGY TENTH EDITION Reece Urry Cain Wasserman Minorsky Jackson Outline I. Organic compounds II. Bonding with Carbon III. Isomers IV. Functional Groups Dr Burns NVC 2014 Pearson Education, Inc. Organic Compounds What is organic We think of organic produce natural In chemistry organic refers to molecules that have a carbon backbone, covalently bound to each other Early chemists thought of organic as coming from plants and animals and inorganic coming from minerals Overview: Carbon: The Backbone of Life Living organisms consist 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 2011 Pearson Education, Inc. Figure 4.1a Carbon Carbon has four valence electrons. It needs eight electrons to be stable So, carbon can form up to four covalent bonds. Carbon can bond to four other atoms or groups of atoms, making a large variety of molecules possible. 1

2 Carbon compounds Molecule Molecular Formula Structural Formula Ball-and-Stick Model Space-Filling Model Carbons can link together to form a backbone many other elements can bond to this backbone (a) Methane CH 4 Carbon carbon bonds are strong (b) Ethane Carbons can form single, double or triple bonds. C 2H 6 Carbons can form chains or rings (c) Ethene (ethylene) C 2H 4 Figure 4.5 Hydrocarbons (a) Length (c) Double bond position Hydrocarbons are organic molecules consisting of only carbon and hydrogen Ethane (b) Branching Propane 1-Butene (d) Presence of rings 2-Butene Many organic molecules, such as fats, have hydrocarbon components Butane 2-Methylpropane (isobutane) Cyclohexane Benzene Hydrocarbons can undergo reactions that release a large amount of energy Figure 4.6 Isomers Nucleus Fat droplets Isomers are compounds with the same molecular formula but different structures and properties Structural isomers have different covalent arrangements of their atoms Cis-trans isomers have the same covalent bonds but differ in spatial arrangements 10 μm (a) Part of a human adipose cell (b) A fat molecule Enantiomers are isomers that are mirror images of each other 2

3 (a) Structural isomers Animation: Isomers Pentane 2-methyl butane (b) Cis-trans isomers cis isomer: The two Xs are on the same side. trans isomer: The two Xs are on opposite sides. (c) Enantiomers CO 2 H CO 2 H H C NH 2 NH 2 C H CH 3 CH 3 L isomer D isomer Structural Isomers Molecule have different arrangement of their carbon skeleton but still have the same molecular formula: Cis-trans Isomers Have the same arrangement of atoms but the spatial arrangement of the atoms are different. An example is cis vs trans arrangements across a double bond (cis = large groups are on same side, trans = large groups on opposite side Enantiomers Enantiomers Isomers that are mirror images of each other Must be a chiral molecule where a carbon is bonded to four different molecules Referred to as: + or R or L 3

4 Why do we care Why do we care The function of a protein is determined by its shape. Usually only one form of an isomer is active in biological systems. Biological organisms usually synthesize only one form. However, chemical synthesis usually produces equal amounts of the two enantiomers Enantiomers are important in the pharmaceutical industry Two enantiomers of a drug may have different effects Usually only one isomer is biologically active Differing effects of enantiomers demonstrate that organisms are sensitive to even subtle variations in molecules Animation: L-Dopa Right-click slide / select Play 2011 Pearson Education, Inc Pearson Education, Inc. Figure 4.8 Drug Condition Effective Enantiomer Ineffective Enantiomer Example: The drug albuterol (e.g., Proventil ) contains equal amounts of two enantiomers. Ibuprofen Pain; inflammation S-Ibuprofen R-Ibuprofen Another more expensive drug is levalbuterol (Xopenex ) it only contains the active form of the drug, it has fewer side effects Albuterol Asthma R-Albuterol S-Albuterol 4

5 This is an example of what kind of isomer? Functional Groups 1. Cis-trans 2. Enantiomers 3. Structural 4. None of the above 25% 25% 25% 25% Functional groups are the components of organic molecules that are most commonly involved in chemical reactions The number and arrangement of functional groups give each molecule its unique properties Geometric Enantiomers Structural None of the above 2011 Pearson Education, Inc. Functional Groups Estradiol Testosterone Groups of atoms; determines the types of chemical reactions and associations 1. Hydroxyl 2. Carbonyl 3. Carboxyl 4. Amino 5. Sulfhydryl 6. Phosphate 7. Methyl Polarity Chemical Group Compound Name Examples Hydroxyl group ( OH) Alcohol Ethanol Carbonyl group ( C=O) Ketone Aldehyde Remember that C-H and C-C bonds are non polar Carboxyl group ( COOH) Carboxylic acid, or organic acid Acetone Propanal Acetic acid Amino group ( NH 2) Amine S, N, and O are electronegative atoms and can make a molecule more polar. Sulfhydryl group ( SH) Thiol Glycine Cysteine Polar and ionic functional groups are hydrophilic, and strongly associate with water Phosphate group ( OPO 3 2 ) Methyl group ( CH 3) Organic phosphate Methylated compound Glycerol phosphate 5-Methyl cytosine 5

6 Properties of functional Groups 1. Hydroxyl polar, can form hydrogen bonds 2. Carbonyl polar, can form hydrogen bonds 3. Carboxyl very polar, weakly acidic and can ionize to become -COO - + H + Important in amino acids 4. Amino - Polar and weakly basic, can accept a H + to become NH 3 + Important in amino acids and nucleic acids Properties of functional Groups 5. Sulfhydryl also called thiol, polar, important in proteins, can form strong S-S bonds that stabilize structure 6. Phosphate polar and weakly acidic. Can dissociate to PO 4-2 Important in nucleic acids and some lipids 7. Methyl nonpolar hydrocarbon Figure 4.9aa Figure 4.9ab Hydroxyl group ( OH) (may be written HO ) Ethanol, the alcohol present in alcoholic beverages Polar due to electronegative oxygen. Forms hydrogen bonds with water. Compound name: Alcohol Carbonyl group ( C=O) Acetone, the simplest ketone Sugars with ketone groups are called ketoses; those with aldehydes are called aldoses. Compound name: Ketone or aldehyde Propanal, an aldehyde Figure 4.9ac Figure 4.9ad Carboxyl group ( COOH) Amino group ( NH 2 ) Acetic acid, which gives vinegar its sour taste Ionized form of COOH (carboxylate ion), found in cells Glycine, an amino acid (note its carboxyl group) Ionized form of NH 2, found in cells Acts as an acid. Compound name: Carboxylic acid, or organic acid Acts as a base. Compound name: Amine 6

7 Figure 4.9ba Figure 4.9bb Sulfhydryl group ( SH) (may be written HS ) Cysteine, a sulfurcontaining amino acid Phosphate group ( OPO 3 2 ) Glycerol phosphate, which takes part in many important chemical reactions in cells Two SH groups can react, forming a cross-link that helps stabilize protein structure. Compound name: Thiol Contributes negative charge. When attached, confers on a molecule the ability to react with water, releasing energy. Compound name: Organic phosphate Figure 4.9bc Carboxyl functional groups are: Methyl group ( CH 3 ) 5-Methyl cytosine, a component of DNA that has been modified by addition of a methyl group 1. Polar 2. Acidic 3. Nonpolar 4. Polar and acidic 25% 25% 25% 25% Affects the expression of genes. Affects the shape and function of sex hormones. Compound name: Methylated compound Polar Acidic Nonpolar Polar and acidic Important Concepts Read Chapters 5 for next lecture Know the vocabulary of the lecture Understand the importance of carbon in organic molecules What are the different types of isomers? Be able to identify examples of each type of isomer. What are the structure and the properties of the common functional groups? 7