Carbon and the Molecular Diversity of Life

Learning Objectives

• Explain why carbon is unparalleled in its ability to form large, diverse molecules.

• Define organic compounds, hydrocarbons, a carbon skeleton, and an isomer.

• Identify the chemical groups important in the chemistry of life.

Organic Chemistry: The Study of Carbon Compounds

Definition and Importance

Organic chemistry is the branch of chemistry that studies compounds containing carbon. Carbon's unique properties make it the backbone of biological molecules.

• Valence refers to the number of covalent bonds an atom can form. Key elements in organic molecules include:

  • Hydrogen (H): Valence = 1

  • Oxygen (O): Valence = 2

  • Nitrogen (N): Valence = 3

  • Carbon (C): Valence = 4

• Carbon can form stable covalent bonds with many elements, including itself, enabling the formation of large and complex molecules.

Carbon's Bonding and Molecular Diversity

Carbon's Four Covalent Bonds

With four valence electrons, carbon can form up to four covalent bonds with other atoms, allowing for a wide variety of molecular structures.

Additional info: The table above demonstrates how carbon's bonding versatility leads to different molecular shapes and properties.

Molecular Diversity from Carbon Skeletons

Carbon skeletons can vary in several ways, contributing to the diversity of organic molecules:

• Length: Carbon chains can be short or long (e.g., ethane vs. propane).

• Branching: Chains may be unbranched or branched (e.g., butane vs. 2-methylpropane).

• Double Bond Position: Double bonds can occur at different positions (e.g., 1-butene vs. 2-butene).

• Presence of Rings: Carbon skeletons may form rings (e.g., cyclohexane, benzene).

Example: Benzene (C6H6) is a ring structure important in many biological molecules.

Hydrocarbons

Definition and Biological Significance

Hydrocarbons are organic molecules consisting entirely of carbon and hydrogen. They are hydrophobic and can store large amounts of energy.

• Found in biological molecules such as fats.

• Major components of fossil fuels (e.g., petroleum, natural gas).

Example: Fat molecules contain long hydrocarbon tails, which store energy for living organisms.

Isomers

Types and Importance

Isomers are compounds with the same molecular formula but different structures and properties. The three main types are:

• Structural Isomers: Differ in the covalent arrangement of atoms (e.g., pentane vs. 2-methylbutane).

• Cis-Trans Isomers (Geometric Isomers): Differ in spatial arrangement around a double bond.

  • Cis isomer: The two X groups are on the same side of the double bond.

  • Trans isomer: The two X groups are on opposite sides.

• Enantiomers: Isomers that are mirror images of each other, often with different biological activities.

Example: Enantiomers of a drug may have different effects in the body; one may be therapeutic, the other inactive or harmful.

Chemical Groups Important in the Chemistry of Life

Functional Groups

Certain chemical groups, called functional groups, are key to the function of biological molecules. They attach to carbon skeletons and confer specific chemical properties.

Example: The presence of a phosphate group in ATP (adenosine triphosphate) is critical for energy transfer in cells.

ATP: An Important Source of Energy

Adenosine triphosphate (ATP) is an organic molecule that stores and transfers energy within cells. It contains three phosphate groups, and energy is released when one phosphate group is removed:

Additional info: ATP hydrolysis powers many cellular processes, including muscle contraction and active transport.