Carbon and the Molecular Diversity of Life

Transcription

1 LECTURE PRESENTATIONS For CAMPBELL BIOLOGY, NINTH EDITION Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson Chapter 4 Carbon and the Molecular Diversity of Life Lectures by Erin Barley Kathleen Fitzpatrick

2 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 (versus inanimate objects) are all composed of carbon compounds

3 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

4 Vitalism, the idea that organic compounds arise only in organisms, was disproved when chemists synthesized these compounds In the mid-1800 s, Herman Kolbe made the organic compound acetic acid from inorganic substances that could be prepared directly from pure elements. Mechanism is the view that all natural phenomena are governed by physical and chemical laws

5 Can organic molecules form under conditions believed to simulate those on the early Earth? Sea Mixture of Gases Lightening

6 Organic Molecules and the Origin of Life on Earth Stanley Miller s classic experiment demonstrated the abiotic (non-living) synthesis of organic compounds Experiments support the idea that abiotic synthesis of organic compounds, perhaps near volcanoes, could have been a stage in the origin of life Organic chemistry was redefined as the study of carbon compounds, regardless of origin.

7 Figure the atmosphere contained a mixture of hydrogen gas, methane, ammonia, and water vapor. EXPERIMENT Water vapor CH 4 Atmosphere Electrode 3. Sparks were discharged to mimic lightening. Condenser 1. sea water was heated; vapor entered the atmosphere flask Cooled rain containing organic molecules H 2 O sea Sample for chemical analysis Cold water 4. A condenser cooled the atmosphere, raining water and any dissolved molecules down into the flask. 5. As material cycled through the apparatus, Miller periodically collected samples for analysis.

8 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

9 The Formation of Bonds with Carbon With four valence electrons, carbon can form four covalent bonds with a variety of atoms A valence electron is an electron that is associated with an atom, and that can participate in the formation of a chemical bond This ability makes large, complex molecules possible In molecules with multiple carbons, each carbon bonded to four other atoms has a tetrahedral shape 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

10 H H C H H Methane CH 4 1 carbon and 4 hydrogen When a carbon atom has four single bonds to other atoms, the molecule is tetrahedral (tetra = 4)

11 The electron configuration of carbon gives it covalent compatibility with many different elements The valences of carbon and its most frequent partners (hydrogen, oxygen, and nitrogen) are the building code that governs the architecture of living molecules A carbon atom can also use one or more valence electrons to form covalent bonds to other carbon atoms, linking the atoms into chains of infinite variety!

12 Figure 4.3 Name and Comment Molecular Formula Structural Formula Ball-and- Stick Model Space-Filling Model (a) Methane CH 4 Tetrahedral (b) Ethane C 2 H 6 Tetrahedral (2) (c) Ethene (ethylene) C 2 H 4 1 plane

13 Figure 4.4 Figure 4.4 Valences of the major elements of organic molecules. Hydrogen (valence 1) Oxygen (valence 2) Nitrogen (valence 3) Carbon (valence 4) To determine the valence number, ask: how many more electrons does it need to fill the outermost shell? That is how many chemical bonds the atom can have.

14 What is a double bond? Carbon atoms can partner with atoms other than hydrogen; for example: Can someone go up to Carbon dioxide: CO 2 the board and draw the electron distribution diagram for CO 2? Is CO 2 considered organic? Why or why not? Urea: CO(NH 2 ) 2 Urea

15 Molecular Diversity Arising from Carbon Skeleton Variation Carbon chains form the skeletons (or backbone) of most organic molecules Carbon chains (carbons linked together) vary in length and shape

16 Animation: Carbon Skeletons Right-click slide/select Play

17 Figure 4.5 Figure 4.5 Four ways that carbon skeletons can vary. (a) Length (c) Double bond position Ethane Propane 1-Butene 2-Butene (b) Branching (d) Presence of rings Butane 2-Methylpropane (isobutane) Cyclohexane Benzene

18 Hydrocarbons Hydrocarbons are the major components of petroleum, which is called a fossil fuel. Why do we call them fossil fuels? THINK, PAIR, SHARE! 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 What common role does petroleum for cars and the fat in our bodies play? THINK, PAIR, SHARE!

19 Figure 4.6 Nucleus Fat droplets Long hydrocarbon tails attached to a nonhydrocarbon component. 10 m (a) Part of a human adipose cell (b) A fat molecule Hydrocarbons are not prevalent in most living organisms, but many of a cell s organic molecules have regions consisting of only carbon and hydrogen. Why is fat considered hydrophobic? THINK PAIRE SHARE!

20 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 have the same covalent bonds but differ in spatial arrangements Enantiomers are isomers that are mirror images of each other We will discuss trans fats in the next chapter.

21 Animation: Isomers Right-click slide / select Play

22 Figure 4.7 (a) Structural isomers (b) Cis-trans isomers To help you remember: Cis and Same both start with an S sound. cis isomer: The two Xs are on the same side. (c) Enantiomers CO 2 H trans isomer: The two Xs are on opposite sides. CO 2 H H NH 2 CH 3 L isomer NH 2 CH 3 D isomer H Latin for left is levo and for right is dextro

23 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

24 Ibuprofen reduces inflammation and pain. It is commonly sold as a mixture of 2 enantiomers. The S is 100X more effective than the other. Albuterol is used to relax bronchial muscles, improving airflow. Only R is synthesized and sold as a drug. Figure 4.8 Drug Condition Effective Enantiomer Ineffective Enantiomer Ibuprofen Pain; inflammation S-Ibuprofen R-Ibuprofen Albuterol Asthma R-Albuterol S-Albuterol

25 Concept 4.3: A few chemical groups are key to the functioning of biological molecules Distinctive properties of organic molecules depend on the carbon skeleton and on the molecular components attached to it A number of characteristic groups can replace the hydrogens attached to skeletons of organic molecules

26 The Chemical Groups Most Important in the Processes of Life 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

27 Figure 4.UN02 Estradiol Testosterone The female and male sex hormones have the same basic shape, but they differ in functional groups. Even our sexuality has its biological basis in variations of molecular architecture!

28 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 These are hydrophilic and can increase the solubility of organic compounds in water. Methyl is not reactive.

29 Figure 4.9-a CHEMICAL GROUP Hydroxyl Carbonyl Carboxyl STRUCTURE (may be written HO ) NAME OF COMPOUND Alcohols (Their specific names usually end in -ol.) Ketones if the carbonyl group is within a carbon skeleton Carboxylic acids, or organic acids Aldehydes if the carbonyl group is at the end of the carbon skeleton EXAMPLE EtOH s polarity came into question during our last lab Ethanol Acetone Propanal Acetic acid Which is a ketone? FUNCTIONAL PROPERTIES Is polar as a result of the electrons spending more time near the electronegative oxygen atom. Can form hydrogen bonds with water molecules, helping dissolve organic compounds such as sugars. A ketone and an aldehyde may be structural isomers with different properties, as is the case for acetone and propanal. Ketone and aldehyde groups are also found in sugars, giving rise to two major groups of sugars: ketoses (containing ketone groups) and aldoses (containing aldehyde groups). Acts as an acid; can donate an H + because the covalent bond between oxygen and hydrogen is so polar: Nonionized Ionized Found in cells in the ionized form with a charge of 1 and called a carboxylate ion.

30 Figure 4.9-b Amino Sulfhydryl Phosphate Methyl (may be written HS ) Amines AmiNo groups have Nitrogens Thiols Sulfhydryls have -SH Organic phosphates PhOsphates have P s and O s Methylated compounds Glycine Cysteine Glycerol phosphate 5-Methyl cytidine Acts as a base; can pick up an H + from the surrounding solution (water, in living organisms): Nonionized Found in cells in the ionized form with a charge of 1+. Ionized Two sulfhydryl groups can react, forming a covalent bond. This cross-linking helps stabilize protein structure. Cross-linking of cysteines in hair proteins maintains the curliness or straightness of hair. Straight hair can be permanently curled by shaping it around curlers and then breaking and re-forming the cross-linking bonds. Contributes negative charge to the molecule of which it is a part (2 when at the end of a molecule, as above; 1 when located internally in a chain of phosphates). Molecules containing phosphate groups have the potential to react with water, releasing energy. Addition of a methyl group to DNA, or to molecules bound to DNA, affects the expression of genes. Arrangement of methyl groups in male and female sex hormones affects their shape and function.

31 Be able to recognize these groups and some of their characteristics! Which functional group is not present in this molecule? Which chemical group is most likely to be responsible for an organic molecule behaving as a base? Hydroxyl Carbonyl Carboxyl Amino Phosphate

32 ATP: An Important Source of Energy for Cellular Processes One phosphate molecule, adenosine triphosphate (ATP), is the primary energytransferring molecule in the cell ATP consists of an organic molecule called adenosine attached to a string of three phosphate groups

33 Figure 4. UN04 Adenosine

34 Figure 4. UN05 Adenosine Triphosphate (ADP) Adenosine Reacts with H 2 O Adenosine Energy ATP Inorganic phosphate ADP Adenosine Diphosphate (ADP)

35 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