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

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

             Vitalism, the idea that organic compounds arise only in organisms, was disproved when chemists synthesized these compounds

             Mechanism is the view that all natural phenomena are governed by physical and chemical laws

Organic Molecules and the Origin of Life on Earth

             Stanley Miller’s classic experiment demonstrated the abiotic 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

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

The Formation of Bonds with Carbon

             With four valence electrons, carbon can form four covalent bonds with a variety of atoms

             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

             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

             Carbon atoms can partner with atoms other than hydrogen; for example:

            Carbon dioxide: CO2

            Urea: CO(NH2)2

Molecular Diversity Arising from Carbon Skeleton Variation

             Carbon chains form the skeletons of most organic molecules

             Carbon chains vary in length and shape


             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 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

             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

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

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

             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

ATP: An Important Source of Energy for Cellular Processes

             One phosphate molecule, adenosine triphosphate (ATP), is the primary energy-transferring molecule in the cell

             ATP consists of an organic molecule called adenosine attached to a string of three phosphate groups

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