3.1 Carbon Atoms and the Diversity of Organic Molecules

CHNOPS: The Six Most Common Elements in Living Things

Living organisms are primarily composed of six essential elements, often remembered by the mnemonic CHNOPS:

• Carbon (C)

• Hydrogen (H)

• Nitrogen (N)

• Oxygen (O)

• Phosphorus (P)

• Sulfur (S)

These elements form the molecular foundation for all known life forms.

Definition of "Organic" in Biology

• Organic compounds must contain carbon, have at least one carbon-hydrogen bond, and be made by a cell.

• The simplest organic molecule is methane (CH4).

• Inorganic compounds may contain carbon but do not contain carbon-hydrogen bonds or are not made by cells (e.g., carbon dioxide, carbon monoxide).

Special Properties of Carbon

• Carbon atoms can form four covalent bonds, allowing for a wide variety of stable compounds.

• This versatility makes carbon the backbone of biological molecules.

Carbon Skeletons: Structural Diversity

Carbon skeletons can vary in several ways, contributing to molecular diversity:

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

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

• Double Bond Position: Double bonds can be in different locations (e.g., 1-butene vs. 2-butene).

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

Isomerism in Organic Molecules

Types of Isomers

Isomers are compounds with the same molecular formula but different structures and properties.

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

• Cis-Trans (Geometric) Isomers: Differ in spatial arrangement around a double bond. Cis isomers have groups on the same side; trans isomers have groups on opposite sides.

• Enantiomers: Mirror-image isomers due to an asymmetric carbon (chiral center). They are non-superimposable and can have different biological activities.

ATP: The Energy Currency of the Cell

Structure and Function of ATP

• Adenosine Triphosphate (ATP) is the primary energy carrier in cells.

• ATP consists of adenine, ribose (a sugar), and three phosphate groups.

• Energy is stored in the high-energy phosphate bonds.

• When ATP is hydrolyzed (ATP → ADP + Pi), energy is released for cellular work.

Key Equation:

• ATP is used for processes such as biosynthesis, active transport, and movement.

• ATP cannot be stored long-term; energy is stored as starch, glycogen, or fats.

Three Classes of Organic Macromolecules

Overview Table: Major Macromolecules

3.2 Macromolecules: Polymers Built from Monomers

Four Major Groups of Organic Molecules

• Carbohydrates

• Lipids

• Proteins

• Nucleic Acids

These macromolecules are essential for life and are built from smaller subunits called monomers.

Monomers and Polymers

• Monomer: The smallest repeating subunit of a macromolecule (e.g., amino acid, nucleotide, monosaccharide).

• Polymer: A large molecule made by joining many monomers together (e.g., protein, DNA, polysaccharide).

• Polymerization: The process of linking monomers to form polymers.

How Monomers Link to Form Polymers

• Monomers are joined by covalent bonds in a process called dehydration synthesis (removal of water).

• Polymers can be broken down into monomers by hydrolysis (addition of water).

Examples of Polymer Formation

• Proteins: Amino acids are joined by peptide bonds to form polypeptides.

• Carbohydrates: Monosaccharides are joined by glycosidic bonds to form disaccharides and polysaccharides.

Additional info: The notes also reference the importance of ATP as a nucleotide derivative and the role of macromolecules in cellular structure and function.