Chapter 4: Carbon and the Molecular Diversity of Life

Properties of Carbon and Its Importance in Living Organisms

Carbon is a fundamental element in biological molecules due to its unique chemical properties. Its ability to form four covalent bonds allows for the construction of complex and diverse organic molecules essential for life.

• Tetravalence: Carbon has four valence electrons, enabling it to form up to four covalent bonds with other atoms, including other carbon atoms.

• Versatility: Carbon can form single, double, or triple bonds, and can create chains, branched molecules, or rings.

• Backbone of Organic Molecules: The diversity of carbon skeletons forms the basis for the variety of organic molecules found in living organisms.

• Example: Glucose (C6H12O6) is a simple sugar with a carbon backbone that is essential for cellular respiration.

The Vitalism Theory and Its Discarding

Vitalism was the belief that organic compounds could only be produced by living organisms through a "vital force." This theory was eventually disproven by scientific experiments.

• Vitalism: The idea that organic molecules could not be synthesized from inorganic components outside of living systems.

• Key Scientists: Friedrich Wöhler synthesized urea (an organic compound) from inorganic ammonium cyanate in 1828, demonstrating that organic molecules could be created artificially.

• Impact: This experiment helped establish the field of organic chemistry and showed that the same physical and chemical laws apply to both living and non-living matter.

• Example: Wöhler’s synthesis of urea:

Organic and Inorganic Compounds; Hydrocarbons; Hydrophobic and Hydrophilic Properties; Functional Groups

Organic compounds are primarily made of carbon atoms bonded to hydrogen, oxygen, nitrogen, and other elements. Their properties depend on the types of bonds and functional groups present.

• Organic Compounds: Molecules containing carbon and usually hydrogen; examples include carbohydrates, proteins, lipids, and nucleic acids.

• Inorganic Compounds: Compounds that do not primarily contain carbon-hydrogen bonds; examples include water, salts, and minerals.

• Hydrocarbons: Organic molecules consisting entirely of carbon and hydrogen. They are nonpolar and hydrophobic (do not dissolve in water).

• Hydrophobic vs. Hydrophilic:

  • Hydrophobic: Molecules that repel water (e.g., hydrocarbons).

  • Hydrophilic: Molecules that interact well with water, often due to the presence of polar functional groups (e.g., alcohols, carboxylic acids).

• Functional Groups: Specific groups of atoms within molecules that determine the chemical properties and reactions of those molecules. Common functional groups include:

• Predicting Hydrophilic/Hydrophobic Nature: The presence of polar or charged functional groups (e.g., hydroxyl, carboxyl, amino, phosphate) makes a molecule hydrophilic, while nonpolar groups (e.g., methyl, hydrocarbon chains) make it hydrophobic.

Isomerism: Structural Isomers, Cis-Trans Isomers, Enantiomers

Isomers are compounds with the same molecular formula but different structures and properties. The diversity of isomers contributes to the complexity and functionality of organic molecules.

• Structural Isomers: Molecules with the same molecular formula but different covalent arrangements of atoms.

• Cis-Trans Isomers (Geometric Isomers): Isomers that differ in the spatial arrangement of atoms around a double bond or ring structure.

  • Cis: Same side of the double bond.

  • Trans: Opposite sides of the double bond.

• Enantiomers: Isomers that are mirror images of each other and cannot be superimposed. They arise from the presence of an asymmetric carbon (a carbon attached to four different groups).

• Asymmetric Carbon: A carbon atom bonded to four different atoms or groups, leading to chirality.

• Biological Importance: Enantiomers can have drastically different effects in biological systems (e.g., one enantiomer of a drug may be therapeutic, while the other is inactive or harmful).

• Example: L- and D- forms of amino acids; only L-amino acids are used in proteins.