4 Carbon and the Molecular Diversity of Life

Transcription

1 4 Carbon and the Molecular Diversity of Life CAMPBELL BIOLOGY TENTH EDITION Reece Urry Cain Wasserman Minorsky Jackson Lecture Presentation by Nicole Tunbridge and Kathleen Fitzpatrick Vitalism vs Mechanism Vitalism vs Mechanism Vitalism was the belief in a life force outside the jurisdiction of physical and chemical laws 1) It was thought that organic compounds could only be produced in living organisms 2) Vitalism was disproved when chemists were able to synthesize organic compounds Mechanism is the view that physical and chemical laws govern all natural phenomena living organisms can be understood in terms of the same physical and chemical laws that can be used to explain all natural phenomena 1

2 Hadean ERA 4.2 to 3.5 Billion years ago Organic Molecules and the Origin of Life on Earth Stanley Miller s (1953) classic experiment demonstrated the abiotic synthesis of organic compounds from inorganic compounds Figure 4.Scientific Skills Some of Stanley Miller s notes from his 1958 hydrogen sulfide (H 2 S) experiment First biological molecules near a volcano? H 2 S Some of Stanley Miller s original vials from his 1958 hydrogen sulfide (H 2 S) experiment 2

3 Figure 4.1 carbon-based lifeforms CHON 96% CaPPSS 4% Concept 4.1: Organic chemistry is the study of carbon compounds Organic chemistry is the study of compounds that contain carbon Organic compounds range from simple molecules to colossal ones Most organic compounds contain hydrogen atoms in addition to carbon atoms not a hard and fast rule e.g. Urea, Mellitic acid does not contain C-H bonds Mellitic acid possible organic substance in Martian soil UREA 3

4 Carbon: The Backbone of Life Living organisms consist mostly of carbon-based compounds - Carbon is present in all organic molecules Proteins, DNA, carbohydrates, and other molecules that distinguish living matter are all composed of carbon compounds Carbon is unparalleled in its ability to form large, complex, and varied molecules 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 Carbon can bond to four other atoms or groups of atoms, making a large variety of molecules possible. The complexity and variety of organic molecules is due to the chemical versatility of carbon atoms Figure 4.4 Review bonds Hydrogen (valence = 1) Oxygen (valence = 2) Nitrogen (valence = 3) Carbon (valence = 4) Single covalent bond Double covalent bond 4

5 The Formation of Bonds with Carbon With four valence electrons, carbon can form four covalent bonds with a variety of atoms The electron configuration of carbon gives it covalent compatibility with many different elements - most frequent partners (carbon, hydrogen, oxygen, and nitrogen) making up most of living molecules C O C H N e.g. Hydrocarbons Hydrocarbons are organic molecules consisting of only carbon and hydrogen Many organic molecules, such as fats, have hydrocarbon components Hydrocarbons can undergo reactions that release a large amount of energy Homework due on Thursday Why is this component of fat molecule hydrophobic? 5

6 Molecular Diversity Arising from Variation in Carbon Skeletons This ability makes large, complex molecules possible Carbon chains form the skeletons of most organic molecules Carbon chains vary in length and shape Straight Branched rings of atom Start thinking in 3d Shapes are very important In biology The Formation of Bonds with Carbon With four valence electrons, carbon can form four covalent bonds with a variety of atoms The 3d shapes possible are If single bonds - In molecules with multiple carbons, each carbon bonded to four other atoms has a tetrahedral shape If double bonds - However, when two carbon atoms are joined by a double bond, the atoms joined to the carbons are in the same plane as the carbons 6

7 Figure 4.3 Molecule Molecular Formula Structural Formula Ball-and-Stick Model Space-Filling Model (a) Methane CH 4 (b) Ethane C 2H 6 (c) Ethene (ethylene) C 2H 4 Isomers 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/geometric isomers have the same covalent bonds but differ in spatial arrangements Enantiomers are isomers that are mirror images of each other Figure 4.7 (a) Structural isomers Pentane 2-methyl butane (b) Cis-trans isomers/geometric isomers cis isomer: The two Xs are on the same side. trans isomer: The two Xs are on opposite sides. (c) Enantiomers/ stereoisomers CO 2H CO 2H H C NH2 NH 2 C H CH 3 CH 3 L isomer D isomer 7

8 Number And Type same Arrangement different Structural isomers Animation: Isomers 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 8

9 Animation: L-Dopa Concept 4.3: A few chemical groups are key to molecular function Distinctive properties of organic molecules depend on the carbon skeleton and on the chemical groups attached to it A number of characteristic groups can replace the hydrogens attached to skeletons of organic molecules 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 The Chemical Groups are important for the function of molecules Estradiol and testosterone are both steroids with a common carbon skeleton, in the form of four fused rings These sex hormones differ only in the chemical groups attached to the rings of the carbon skeleton 9

10 Figure 4.9 Chemical Group Compound Name Examples Hydroxyl group ( OH) Alcohol Ethanol Carbonyl group ( C=O) Ketone Aldehyde Acetone Propanal Carboxyl group ( COOH) Carboxylic acid, or organic acid Acetic acid Amino group ( NH 2 ) Amine Glycine Sulfhydryl group ( SH) Thiol Cysteine Phosphate group ( OPO 3 2 ) Organic phosphate Glycerol phosphate Methyl group ( CH 3) Methylated compound 5-Methyl cytosine Figure 4.9aa 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 Figure 4.9ab Carbonyl group ( C=O) Acetone, the simplest ketone Propanal, an aldehyde Sugars with ketone groups are called ketoses; those with aldehydes are called aldoses. Compound name: Ketone or aldehyde 10

11 Figure 4.9ac Carboxyl group ( COOH) Acetic acid, which gives vinegar its sour taste Ionized form of COOH (carboxylate ion), found in cells Acts as an acid. Compound name: Carboxylic acid, or organic acid Figure 4.9a Chemical Group Compound Name Examples Hydroxyl group ( OH) Alcohol Ethanol Carbonyl group ( C=O) Ketone Aldehyde Carboxyl group ( COOH) Carboxylic acid, or organic acid Acetone Propanal Acetic acid Amino group ( NH 2) Amine Glycine Figure 4.9b Chemical Group Compound Name Examples Sulfhydryl group ( SH) Thiol Cysteine Phosphate group ( OPO 3 2 ) Organic phosphate Glycerol phosphate Methyl group ( CH 3 ) Methylated compound 5-Methyl cytosine 11

12 ATP: An Important Source of Energy for Cellular Processes An important organic phosphate is adenosine triphosphate (ATP) ATP consists of an organic molecule called adenosine attached to a string of three phosphate groups ATP stores the potential to react with water, a reaction that releases energy to be used by the cell Adenosine Figure 4.UN04 Adenosine Reacts with H 2 O P P P Adenosine P i P P ATP Inorganic phosphate Adenosine ADP Energy The Chemical Elements of Life: A Review The versatility of carbon makes possible the great diversity of organic molecules Variation at the molecular level lies at the foundation of all biological diversity Different organisms are different because of types and relative amounts of organic molecules 12