Chapter 4 Carbon jprthpwoirhtpwoith

Overview: Carbon—The Backbone of Biological Molecules Carbon can form large, complex, and diverse molecules, including “biological macromolecules” Proteins, DNA, carbohydrates, lipids, and other molecules that distinguish living matter are all composed of carbon compounds

LE 4-4 Carbon (valence = 4)

The Formation of Bonds with Carbon With four valence electrons, carbon can form four covalent bonds with a variety of atoms This tetravalence 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 molecule has a flat shape

Molecular Formula Structural Formula Ball-and-Stick Model Space-Filling Model Methane Ethane Ethene (ethylene)

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

LE 4-4 Hydrogen (valence = 1) Oxygen (valence = 2) Nitrogen (valence = 3) Carbon (valence = 4)

Molecular Diversity Arising from Carbon Skeleton Variation Carbon chains form the skeletons of most organic molecules Carbon chains vary in length and shape

Concept 4.3: Functional groups are the parts of molecules involved in chemical reactions Distinctive properties of organic molecules depend not only on the carbon skeleton but also on the molecular components attached to it Certain groups of atoms are often attached to skeletons of organic molecules

The Functional Groups Most Important in the Chemistry 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

The six functional groups that are most important in the chemistry of life:

Hydroxyl group - O - H NAME OF COMPOUNDS Alcohols (their specific names usually end in -ol) FUNCTIONAL PROPERTIES Is polar as a result of the electronegative oxygen atom drawing electrons toward itself. Ethanol, the alcohol present in alcoholic beverages Attracts water molecules, helping dissolve organic compounds such as sugars (see Figure 5.3).

Ketones if the carbonyl group is LE 4-10ab STRUCTURE EXAMPLE Acetone, the simplest ketone NAME OF COMPOUNDS Ketones if the carbonyl group is within a carbon skeleton Propanal, an aldehyde Aldehydes if the carbonyl group is at the end of the carbon skeleton FUNCTIONAL PROPERTIES A ketone and an aldehyde may be structural isomers with different properties, as is the case for acetone and propanal.

Carboxyl NAME OF COMPOUNDS Carboxylic acids, or organic acids

Acetic acid Carboxyl The covalent bond between oxygen and hydrogen is so polar that hydrogen ions (H+) tend to dissociate reversibly; In cells, found in the ionic form, which is called a carboxylate group. FUNCTIONAL PROPERTIES Has acidic properties because it is a source of hydrogen ions. Acetic acid Acetate ion

Amino Glycine Because it also has a carboxyl NAME OF COMPOUNDS Amine Because it also has a carboxyl group, glycine is both an amine and a carboxylic acid; compounds with both groups are called amino acids.

Sulfhydryl Ethanethiol FUNCTIONAL PROPERTIES NAME OF COMPOUNDS Thiols FUNCTIONAL PROPERTIES Two sulfhydryl groups can interact to help stabilize protein structure (see Figure 5.20).

Phosphate (ATP) FUNCTIONAL PROPERTIES NAME OF COMPOUNDS Glycerol phosphate NAME OF COMPOUNDS FUNCTIONAL PROPERTIES Organic phosphates Makes the molecule of which it is a part an anion (negatively charged ion). Can transfer energy between organic molecules. (ATP)

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

Length Propane Ethane

(commonly called isobutane) Branching 2-methylpropane (commonly called isobutane) Butane

Double bonds 1-Butene 2-Butene

Rings Cyclohexane Benzene

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

Isomers Isomers are compounds with the same molecular formula but different structures and properties: Structural isomers have different covalent arrangements of their atoms Geometric isomers have the same covalent arrangements but differ in spatial arrangements Enantiomers are isomers that are mirror images of each other

Structural isomers differ in covalent partners, as shown in this example of two isomers of pentane.

cis isomer: The two Xs are on the same side. trans isomer: The two Xs are on opposite sides. Geometric isomers differ in arrangement about a double bond. In these diagrams, X represents an atom or group of atoms attached to a double-bonded carbon.

L isomer D isomer Enantiomers differ in spatial arrangement around an asymmetric carbon, resulting in molecules that are mirror images, like left and right hands. The two isomers are designated the L and D isomers from the Latin for left and right (levo and dextro). Enantiomers cannot be superimposed on each other.

Enantiomers are important in the pharmaceutical industry Two enantiomers of a drug may have different effects Differing effects of enantiomers demonstrate that organisms are sensitive to even subtle variations in molecules

(effective against Parkinson’s disease) (biologically Inactive) L-Dopa LE 4-8 L-Dopa (effective against Parkinson’s disease) D-Dopa (biologically Inactive)