Carbon and the Molecular Diversity of Life: Biological Molecules (Chapters 4-5) – Study Notes

Carbon and the Molecular Diversity of Life

Atomic Structure and Properties of Carbon

Carbon is a fundamental element in biological molecules due to its unique atomic structure and bonding capabilities.

• Atomic Number: The number of protons (and electrons in a neutral atom) in an atom. For carbon, this is 6.

• Atomic Mass: The mass of an atom, measured in atomic mass units (AMU). For carbon, this is approximately 12.01 AMU.

• Symbol/Name: Carbon is represented by the symbol 'C'.

Why Carbon is the Basis for All Biological Molecules

Carbon's ability to form four covalent bonds makes it exceptionally versatile, allowing it to serve as the backbone for a vast array of complex molecules essential for life.

• Four Bonds: Carbon can form up to four covalent bonds with other atoms, enabling the creation of large, complex molecules.

• Carbon Skeletons: The arrangement of carbon atoms forms the skeleton of organic molecules, which can vary in length, branching, and ring structures.

• Chemical Groups: The properties of carbon-containing molecules depend on the attached chemical groups, influencing molecular function (e.g., dopamine as a signaling molecule).

Formation of Bonds with Carbon

Carbon atoms can form diverse molecules by bonding to four other atoms, resulting in a variety of molecular shapes and properties.

Example	Molecular Formula	Structural Formula	Ball-and-Stick Model	Space-Filling Model
Methane	CH4	H | H–C–H | H	Four single bonds in a tetrahedral shape	Tetrahedral
Ethane	C2H6	H H | | H–C–C–H | | H H	Two tetrahedral carbons joined	Extended tetrahedral
Ethene (Ethylene)	C2H4	H2C=CH2	Planar, double bond between carbons	Flat, planar

Valences of the Major Elements of Organic Molecules

The valence of an atom is the number of covalent bonds it can form, determined by the number of electrons needed to fill its outer shell.

Element	Dot Structure	Electron Distribution	Electrons Needed	Number of Bonds
Hydrogen	H·	1 electron	1	1
Oxygen	·O·	2, 6 electrons	2	2
Nitrogen	·N··	2, 5 electrons	3	3
Carbon	·C··	2, 4 electrons	4	4

The Four Major Classes of Biological Molecules

Overview of Biological Macromolecules

Living organisms are composed of four major classes of biological molecules: carbohydrates, proteins, nucleic acids, and lipids. Three of these classes are macromolecules made of repeating monomer units (polymers).

• Carbohydrates: Serve as energy sources and provide structural support (e.g., starch, glucose).

• Proteins: Perform a wide range of functions, including catalysis (enzymes), transport, and structural roles.

• Nucleic Acids: Store and transmit genetic information (DNA, RNA).

• Lipids: Diverse group not classified as polymers; function in energy storage, membrane structure, and signaling (e.g., phospholipids, steroids).

Polymerization: Macromolecules are formed by joining monomers through dehydration synthesis (removal of water) and broken down by hydrolysis (addition of water).